Network Working Group                                            S. Raza
Internet-Draft                                               J. Hoeglund
Intended status: Standards Track                                 RISE AB
Expires: October 30, November 26, 2021                                   G. Selander
                                                      J. Preuss Mattsson
                                                             Ericsson AB
                                                              M. Furuhed
                                                             Nexus Group
                                                          April 28,
                                                            May 25, 2021

          CBOR Encoded X.509 Certificates (C509 Certificates)
                  draft-ietf-cose-cbor-encoded-cert-00
                  draft-ietf-cose-cbor-encoded-cert-01

Abstract

   This document specifies a CBOR encoding of X.509 certificates.  The
   resulting certificates are called C509 Certificates.  The CBOR
   encoding supports a large subset of RFC 5280 and significantly
   reduces the size of all certificates
   compatible with e.g. the RFC 7925, IEEE 802.1AR (DevID), CNSA, and CA/Browser CA/
   Browser Forum Baseline Requirements. Requirements profiles.  When used to re-encode
   DER encoded X.509 certificates, the CBOR encoding can in many cases
   reduce the size of RFC 7925 profiled certificates with over 50%.  The
   CBOR encoded structure can alternatively be signed directly
   ("natively signed"), which does not require re-encoding for the
   signature to be verified.  The document also specifies COSE headers
   as well as a TLS certificate type for C509 certificates.

   NOTE: "C509" is a placeholder, name to be decided by the COSE WG.

Status of This Memo

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   This Internet-Draft will expire on October 30, November 26, 2021.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   4
   3.  CBOR Encoding . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Message Fields  . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Encoding of subjectPublicKey and issuerSingatureValue . .   8
     3.3.  Encoding of Extensions  . . . . . . . . . . . . . . . . .   9
   4.  Compliance Requirements for Constrained IoT . . . . . . . . .  11  12
   5.  Legacy Considerations . . . . . . . . . . . . . . . . . . . .  11  12
   6.  Expected Certificate Sizes  . . . . . . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12  13
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13  14
     8.1.  C509 Certificate Types Registry . . . . . . . . . . . . .  13  14
     8.2.  C509 Certificate Attributes Registry  . . . . . . . . . .  13  15
     8.3.  C509 Certificate Extensions Registry  . . . . . . . . . .  16  17
     8.4.  C509 Certificate Certificate Policies Registry  . . . . .  19
     8.5.  C509 Certificate Extended Key Usages Registry . . . . . .  18
     8.5.  20
     8.6.  C509 Certificate General Names Registry . . . . . . . . .  19
     8.6.  21
     8.7.  C509 Certificate Signature Algorithms Registry  . . . . .  20
     8.7.  22
     8.8.  C509 Certificate Public Key Algorithms Registry . . . . .  23
     8.8.  25
     8.9.  COSE Header Parameters Registry . . . . . . . . . . . . .  25
     8.9.  27
     8.10. TLS Certificate Types Registry  . . . . . . . . . . . . .  26
     8.10.  28
     8.11. CBOR Tags Registry  . . . . . . . . . . . . . . . . . . .  27  29
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27  29
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  27  29
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  28  30
   Appendix A.  Example C509 Certificates  . . . . . . . . . . . . .  30  32
     A.1.  Example RFC 7925 profiled X.509 Certificate . . . . . . .  30  32
     A.2.  Example IEEE 802.1AR profiled X.509 Certificate . . . . .  34  36
     A.3.  Example CAB Baseline ECDSA HTTPS X.509 Certificate  . . .  34  36
     A.4.  Example CAB Baseline RSA HTTPS X.509 Certificate  . . . .  36  39
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  39  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40  42

1.  Introduction

   One of the challenges with deploying a Public Key Infrastructure
   (PKI) for the Internet of Things (IoT) is the size and parsing of
   X.509 public key certificates [RFC5280], since those are not
   optimized for constrained environments [RFC7228].  Large certificate
   chains are also problematic in non-constrained protocols such as EAP-
   TLS [I-D.ietf-emu-eap-tls13] [I-D.ietf-emu-eaptlscert] where
   authenticators typically drop an EAP session after only 40 - 50
   round-trips and QUIC [I-D.ietf-quic-transport] where the latency
   increases significantly unless the server only send sends less than three times
   as many bytes as received prior to validating the client address.
   More compact certificate representations are therefore desirable in
   many use cases.  Due to the current PKI usage of DER encoded X.509
   certificates, keeping compatibility with DER encoded X.509 is
   necessary at least for a transition period.  However, the use of a
   more compact encoding with the Concise Binary Object Representation
   (CBOR) [RFC8949] reduces the certificate size significantly which has
   known performance benefits in terms of decreased communication
   overhead, power consumption, latency, storage, etc.

   CBOR is a data format designed for small code size and small message
   size.  CBOR builds on the JSON data model but extends it by e.g.
   encoding binary data directly without base64 conversion.  In addition
   to the binary CBOR encoding, CBOR also has a diagnostic notation that
   is readable and editable by humans.  The Concise Data Definition
   Language (CDDL) [RFC8610] provides a way to express structures for
   protocol messages and APIs that use CBOR.  [RFC8610] also extends the
   diagnostic notation.

   CBOR data items are encoded to or decoded from byte strings using a
   type-length-value encoding scheme, where the three highest order bits
   of the initial byte contain information about the major type.  CBOR
   supports several different types of data items, in addition to
   integers (int, uint), simple values (e.g. null), byte strings (bstr),
   and text strings (tstr), CBOR also supports arrays [] of data items,
   maps {} of pairs of data items, and sequences of data items.  For a
   complete specification and examples, see [RFC8949], [RFC8610], and
   [RFC8742].  We recommend implementors to get used to CBOR by using
   the CBOR playground [CborMe].

   CAB Baseline Requirements [CAB-Baseline], RFC 7925 [RFC7925], IEEE
   802.1AR [IEEE-802.1AR], and CNSA [RFC8603] specify certificate
   profiles which can be applied to certificate based authentication
   with, e.g., TLS [RFC8446], QUIC [I-D.ietf-quic-transport], DTLS
   [I-D.ietf-tls-dtls13], COSE [RFC8152], EDHOC [I-D.ietf-lake-edhoc],
   or Compact TLS 1.3 [I-D.ietf-tls-ctls].  RFC 7925 [RFC7925],
   RFC7925bis [I-D.ietf-uta-tls13-iot-profile], and IEEE 802.1AR
   [IEEE-802.1AR] specifically target Internet of Things deployments.
   This document specifies a CBOR encoding based on [X.509-IoT], which
   can support large parts of [RFC5280].  The encoding support all
   [RFC7925] and IEEE 802.1AR [IEEE-802.1AR] and CAB Baseline
   [CAB-Baseline] profiled X.509 certificates.  The resulting
   certificates are called C509 Certificates.  Two variants are defined
   using the same CBOR encoding and differing only in what is being
   signed:

   1.  An invertible CBOR re-encoding of DER encoded X.509 certificates
       [RFC5280], which can be reversed to obtain the original DER
       encoded X.509 certificate.

   2.  Natively signed C509 certificates, where the signature is
       calculated over the CBOR encoding instead of over the DER
       encoding as in 1.  This removes the need for ASN.1 and DER
       parsing and the associated complexity but they are not backwards
       compatible with implementations requiring DER encoded X.509.

   Natively signed C509 certificates can be applied in devices that are
   only required to authenticate to natively signed C509 certificate
   compatible servers, which is not a major restriction for many IoT
   deployments where the parties issuing and verifying certificates can
   be a restricted ecosystem.

   This document specifies COSE headers for use of the C509 certificates
   with COSE, see Section 8.8. 8.9.  The document also specifies a TLS
   certificate type for use of the C509 certificates with TLS and QUIC
   (with or without additional TLS certificate compression), see
   Section 8.9. 8.10.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This specification makes use of the terminology in [RFC5280],
   [RFC7228], [RFC8610], and [RFC8949].  When referring to CBOR, this
   specification always refer to Deterministically Encoded CBOR as
   specified in Sections 4.2.1 and 4.2.2 of [RFC8949].

3.  CBOR Encoding

   This section specifies the content and encoding for C509
   certificates, with the overall objective to produce a very compact
   representation supporting large parts of [RFC5280], and everything in
   [RFC7925], [IEEE-802.1AR], and CAB Baseline [CAB-Baseline].  In the
   CBOR encoding, static fields are elided, elliptic curve points and
   time values are compressed, OID are replaced with short integers, and
   redundant encoding is removed.  Combining these different components
   reduces the certificate size significantly, which is not possible
   with general purpose compression algorithms, see Figure 2. 3.

   The C509 certificate can be either a CBOR re-encoding of a DER
   encoded X.509 certificate, in which case the signature is calculated
   on the DER encoded ASN.1 data in the X.509 certificate, or a natively
   signed C509 certificate, in which case the signature is calculated
   directly on the CBOR encoded data.  In both cases the certificate
   content is adhering to the restrictions given by [RFC5280].  The re-
   encoding is known to work with DER encoded certificates but might
   work with other canonical encodings.  The re-encoding does not work
   for BER encoded certificates.

   In the encoding described below, the order of elements in arrays are
   always encoded in the same order as the elements or the corresponding
   SEQUENCE or SET in the DER encoding.

3.1.  Message Fields

   The X.509 fields and their CBOR encodings are listed below, and used
   in the definition of C509 certificates, see Figure 1.

   C509 certificates are defined in terms of DER encoded [RFC5280] X.509
   certificates:

   o  version.  The 'version' field is encoded in the
      'cborCertificateType'
      'c509CertificateType' CBOR int.  The field 'cborCertificateType' 'c509CertificateType'
      also indicates the type of the C509 certificate.  Currently, the
      type can be a natively signed C509 certificate following X.509 v3
      (cborCertificateType
      (c509CertificateType = 0) or a CBOR re-encoded X.509 v3 DER
      certificate (cborCertificateType (c509CertificateType = 1), see Section 8.1.

   o  serialNumber.  The 'serialNumber' INTEGER value field is encoded
      as the unwrapped CBOR unsigned bignum (~biguint)
      'certificateSerialNumber'.  Any leading 0x00 byte (to indicate
      that the number is not negative) is therefore omitted.

   o  signature.  The 'signature' field is always the same as the
      'signatureAlgorithm' field and therefore omitted from the CBOR
      encoding.

   o  issuer.  In the general case, the sequence of
      'RelativeDistinguishedName' is encoded as a CBOR array of CBOR
      arrays of Attributes.  Typically each RelativeDistinguishedName
      only contains a single attribute and the sequence is then encoded
      as a CBOR array of Attributes.  Each Attribute is encoded as a
      (CBOR int, CBOR text string) pair or as a (unwrapped CBOR OID,
      CBOR bytes) pair.  The absolute value of the CBOR int (see
      Figure 4) 5) encodes the attribute type and the sign is used to
      represent the character string type; positive for Utf8String,
      negative for PrintableString.  In natively signed C509
      certificates all text strings are UTF-8 encoded and all attributes
      SHALL have a positive sign.  Text strings SHALL still adhere to
      any X.509 restrictions, i.e. serialNumber SHALL only contain the
      74 character subset of ASCII allowed by PrintableString and
      countryName SHALL have length 2.  The string types teletexString,
      universalString, and bmpString are not supported.  If Name
      contains a single Attribute containing an utf8String encoded
      'common name' it is encoded as a CBOR text string.  If the text
      string contains an EUI-64 of the form "HH-HH-HH-HH-HH-HH-HH-HH"
      where 'H' is one of the symbol '0'-'9' or 'A'-'F' it is encoded as
      a CBOR byte string of length 8 instead.  EUI-64 mapped from a
      48-bit MAC address (i.e. of the form "HH-HH-HH-FF-FE-HH-HH-HH) is
      encoded as a CBOR byte string of length 6.

   o  validity.  The 'notBefore' and 'notAfter' fields are encoded as
      unwrapped CBOR epoch-based date/time (~time) where the tag content
      is an unsigned integer.  In POSIX time, leap seconds are ignored,
      with a leap second having the same POSIX time as the second before
      it.  Compression of X.509 certificates with the time 23:59:60 UTC
      is therefore not supported.  Note that RFC 5280 mandates encoding
      of dates through the year 2049 as UTCTime, and later dates as
      GeneralizedTime.  The value "99991231235959Z" (no expiration date)
      is encoded as CBOR null.

   o  subject.  The 'subject' is encoded exactly like issuer.

   o  subjectPublicKeyInfo.  The 'AlgorithmIdentifier' field including
      parameters is encoded as the CBOR int 'subjectPublicKeyAlgorithm'
      (see Section 8.7) 8.8) or as an array with an unwrapped CBOR OID tag
      [I-D.ietf-cbor-tags-oid] optionally followed by the parameters
      encoded as a CBOR byte string.  In general, the 'subjectPublicKey'
      BIT STRING value field is encoded as a CBOR byte string.  This
      specification assumes the BIT STRING has zero unused bits and the
      unused bits byte is omitted.  For rsaEncryption and id-
      ecPublicKey, the encoding of subjectPublicKey is further optimized
      as described in Section 3.2.

   o  issuerUniqueID.  Not supported.

   o  subjectUniqueID.  Not supported.

   o  extensions.  The 'extensions' field is encoded as a CBOR array
      where each extension is encoded as either a CBOR int (see
      Section 8.3) followed by an optional CBOR item of any type or an
      unwrapped CBOR OID tag [I-D.ietf-cbor-tags-oid] followed by a CBOR
      bool encoding 'critical' and the DER encoded value of the
      'extnValue' encoded as a CBOR byte string.  If the array contains
      exactly two ints and the absolute value of the first int is 2, the
      array is omitted and the extensions is encoded as a single CBOR
      int with the absolute value of the second int and the sign of the
      first int.  Extensions are encoded as specified in Section 3.3.
      The extensions mandated to be supported by [RFC7925] and
      [IEEE-802.1AR] are given special treatment.  An omitted
      'extensions' field is encoded as an empty CBOR array.

   o  signatureAlgorithm.  The 'signatureAlgorithm' field including
      parameters is encoded as a CBOR int (see Section 8.6) 8.7) or as an
      array with an unwrapped CBOR OID tag [I-D.ietf-cbor-tags-oid]
      optionally followed by the parameters encoded as a CBOR byte
      string.

   o  signatureValue.  In general, the 'signatureValue' BIT STRING value
      field is encoded as the CBOR byte string issuerSignatureValue.
      This specification assumes the BIT STRING has zero unused bits and
      the unused bits byte is omitted.  For natively signed C509
      certificates the signatureValue is calculated over the CBOR
      sequence TBSCertificate.  For ECDSA, the encoding of
      issuerSignatureValue is further optimized as described in
      Section 3.2

   The following Concise Data Definition Language (CDDL) defines
   CBORCertificate the
   CBOR array C509Certificate and TBSCertificate, which are encoded as the CBOR
   Sequences [RFC8742]. sequence [RFC8742]
   TBSCertificate.  The member names therefore only have documentary
   value.  Applications not requiring a CBOR item MAY represent C509
   certificates with the CBOR sequence ~C509Certificate (unwrapped
   C509Certificate).

C509Certificate = [
   TBSCertificate,
   issuerSignatureValue : any,
]

; The elements of the following group are to be used in a CBOR Sequence:
CBORCertificate = (
   TBSCertificate,
   issuerSignatureValue : any,
)
TBSCertificate = (
   cborCertificateType:
   c509CertificateType: int,
   certificateSerialNumber: CertificateSerialNumber,
   issuer: Name,
   validityNotBefore: Time,
   validityNotAfter: Time,
   subject: Name,
   subjectPublicKeyAlgorithm: AlgorithmIdentifier,
   subjectPublicKey: any,
   extensions: Extensions,
   issuerSignatureAlgorithm: AlgorithmIdentifier,
)

CertificateSerialNumber = ~biguint

Name = [ * RelativeDistinguishedName ] / text / bytes

RelativeDistinguishedName = Attribute / [ 2* Attribute ]

Attribute = ( attributeType: int, attributeValue: text ) //
            ( attributeType: ~oid, attributeValue: bytes )

Time = ~time / null

AlgorithmIdentifier = int / ~oid / [ algorithm: ~oid, ? parameters: bytes ]

Extensions = [ * Extension ] / int

Extension = ( extensionID: int, extensionValue: any ) //
            ( extensionID: ~oid, ? critical: bool, true, extensionValue: bytes )
)

                    Figure 1: CDDL for CBORCertificate. C509Certificate.

3.2.  Encoding of subjectPublicKey and issuerSingatureValue

3.2.1.  Encoding of subjectPublicKey

   For RSA public keys (rsaEncryption), the SEQUENCE and INTEGER type
   and length fields are omitted and the two INTEGER value fields
   (modulus, exponent) are encoded as an array of two unwrapped CBOR
   unsigned bignum (~biguint), i.e. [ modulus : ~biguint, exponent :
   ~biguint ].  If the exponent is 65537, the array and the exponent is
   omitted and subjectPublicKey consist of only the modulus encoded as
   an unwrapped CBOR unsigned bignum (~biguint).

   For elliptic curve public keys in Weierstrass form (id-ecPublicKey),
   uncompressed keys are point compressed as defined in Section 2.3.3 of
   [SECG].  If a DER encoded certificate with a point compressed public
   key of type id-ecPublicKey is CBOR encoded, the octets 0xfe and 0xfd
   are used instead of 0x02 and 0x03 in the CBOR encoding to represent
   even and odd y-coordinate, respectively.

3.2.2.  Encoding of issuerSingatureValue

   For ECDSA signatures, the SEQUENCE and INTEGER type and length fields
   as well as the any leading 0x00 byte (to indicate that the number is
   not negative) are omitted.  If the two INTEGER value fields have
   different lengths, the shortest INTEGER value field is padded with
   zeroes so that the two fields have the same length.  The resulting
   byte string is encoded as a CBOR byte string.

3.3.  Encoding of Extensions

   This section details the encoding of the 'extensions' field.  The
   'extensions' field is encoded as a CBOR array where each extensionID
   is encoded as either a CBOR int or a an unwrapped CBOR OID tag.  If
   'extensionID' is encoded an int (see Section 8.3),the 8.3), the sign is used
   to encode if the extension is critical and the 'critical' field is
   omitted.  Critical extensions are encoded with a positive negative sign and
   non-critical extensions are encoded with a negative positive sign.

   The 'extnValue' OCTET STREAM value field is encoded as the CBOR byte
   string 'extensionValue' except for the extensions specified below.
   The 'extensionValue' for the extensions mandated to be
   supported by [RFC7925], [IEEE-802.1AR], and [CAB-Baseline] which are
   encoded as specified below.  For some extensions, only commonly used
   parts are supported by the CBOR encoding.  If unsupported parts are
   used, the CBOR encoding cannot be used.

   CBOR encoding of the following extension values are fully supported:

   o  subjectKeyIdentifier. extensionValue is the value of the
      'keyIdentifier' field encoded as follows: a CBOR byte string.

   o  keyUsage.  The 'KeyUsage' BIT STRING is interpreted as an unsigned
      integer n in network byte order and encoded as a CBOR int.

   o  subjectAltName.  basicConstraints.  If 'cA' = false then extensionValue = -2, if
      'cA' = true and 'pathLenConstraint' is encoded as an array of (int,
      any) pairs where each pair encodes a general name (see
      Section 8.5).  If not present then
      extensionValue = -1, and if 'cA' = true and 'pathLenConstraint' is
      present then extensionValue = pathLenConstraint.

   o  extKeyUsage. extensionValue is encoded as an array of CBOR ints
      (see Section 8.5) or unwrapped CBOR OID tags
      [I-D.ietf-cbor-tags-oid] where each int or OID tag encodes a key
      usage purpose.  If the array contains a single int, the array is
      omitted.

      ExtValueEKU = [ + int / ~oid ] / int

   CBOR encoding of the following extension values are partly supported:

   o  subjectAltName.  If the subject alternatice name only contains
      general names registered in Section 8.6 the extension value can be
      CBOR encoded. extensionValue is encoded as an array of (int, any)
      pairs where each pair encodes a general name (see Section 8.6).
      If subjectAltName contains exactly one dNSName, the array and the
      int are omitted and extensionValue is the dNSName encoded as a
      CBOR text string.  In addition to the general names defined in
      [RFC5280], the hardwareModuleName type of otherName has been given
      its own int due to its mandatory use in IEEE 802.1AR.  When
      'otherName + hardwareModuleName' is used, then [ oid, bytes ] is
      used to identify the pair ( hwType, hwSerialEntries ) directly as
      specified in [RFC4108].

      GeneralNames  Only the general names in Section 8.6 are
      supported.

      ExtValueSAN = [ + GeneralName ] / text
      GeneralName = ( GeneralNameType : int, GeneralNameValue : any )

   o  basicConstraints.  cRLDistributionPoints.  If 'cA' = false then extensionValue = -2, if
      'cA' = true and 'pathLenConstraint' is not present then
      extensionValue = -1, and if 'cA' = true and 'pathLenConstraint' the CRL Distribution Points is
      present then extensionValue = pathLenConstraint.

   o  extKeyUsage. a
      sequence of DistributionPointName, where each
      DistributionPointName contains a single uniformResourceIdentifier,
      the extension value can be CBOR encoded.  The extensionValue is
      encoded as an array of CBOR ints
      (see Section 8.4) or unwrapped CBOR OID tags
      [I-D.ietf-cbor-tags-oid] text strings where each int or OID tag CBOR text
      string encodes a key
      usage purpose. uniformResourceIdentifier.  If the array contains a single int,
      exactly one text string, the array is omitted.

      ExtValueEKU

      ExtValueCDP = [ + int / ~oid 2* text ] / int text

   o  subjectKeyIdentifier. extensionValue is the value  certificatePolicies.  If each PolicyInformation contains at most
      one PolicyQualifierInfo, where all present policyQualifierId are
      of type id-qt-cps and all present qualifiers are of type cPSuri,
      the
      'keyIdentifier' field encoded as a extension value can be CBOR byte string.

   o  authorityKeyIdentifier. extensionValue is encoded.  OIDs registered in
      Section 8.4 are encoded as an array
      where int.

      ExtValueCP = [ + ( CertPolicyId: oid / int, ? CPSuri: text ) ]

   o  authorityKeyIdentifier.  If the value authority key identifier contains
      all of keyIdentifier, certIssuer, and certSerialNumberm or if only
      keyIdentifier is present the 'keyIdentifier' extension value can be CBOR encoded.

      If all three are present a CBOR array is encoded as used, if only
      keyIdentifier is present a CBOR byte
      string, 'GeneralNames' string is encoded like used.

      ExtValueAKI = [ keyIdentifier: bytes,
                      certIssuer: GeneralNames,
                      certSerialNumber: CertificateSerialNumber ]
                    / bytes

   o  authorityInfoAccess.  If all the GeneralNames in subjectAltName, and
      'AuthorityCertSerialNumber'
      authorityInfoAccess are of type uniformResourceIdentifier, the
      extension value can be CBOR encoded.  The accessMethod is encoded
      as ~biguint exactly like
      certificateSerialNumber.  Omitted values an CBOR int (1 for ocsp and 2 for caIssuers).  The
      uniformResourceIdentifiers are encoded as CBOR null.

      ExtValueAKI text strings.

      ExtValueAIA = [ keyIdentifier: bytes / null,
                      certIssuer: GeneralNames / null,
                      certSerialNumber: CertificateSerialNumber / null ] + ( accessMethod : 1 / bytes 2 , uri : text ) ]

   o  cRLDistributionPoints.  signedCertificateTimestamp.  If all the cRLDistributionPoints is a sequence
      of DistributionPointName, it is encoded like subjectAltName, with
      the difference that if cRLDistributionPoints contains exactly one
      uniformResourceIdentifier, the array and the int SCTs are omitted version 1, and
      extensionValue is
      there are no SCT extensions, the uniformResourceIdentifier extension value can be CBOR
      encoded.  LogIDs are encoded as a CBOR
      text string.

   o  authorityInfoAccess.  If authorityInfoAccess consist of only
      uniformResourceIdentifiers it byte strings, the timestamp
      is encoded as and CBOR int (milliseconds since validityNotBefore),
      and the signature is encoded with an array of uris.

      ExtValueAIA (AlgorithmIdentifier, any)
      pair in the same way as issuerSignatureAlgorithm and
      issuerSignatureValue.

      ExtValueSCT = [ + ( ocsp LogID : 1 // caIssuers bstr, timestamp : 2 , uri int,
                          alg : text AlgorithmIdentifier, signature : any ) ]

3.3.1.  Example Encoding of Extensions

   The examples below use values from Section 8.3, Section 8.4, 8.5, and
   Section 8.5: 8.6:

   o  A critical basicConstraints ('cA' = true) without
      pathLenConstraint is encoded as the two CBOR ints -1, -4, -1.

   o  A non-critical keyUsage with digitalSignature and keyAgreement
      asserted is encoded as the two CBOR ints 2, 17 (2^0 + 2^4 = 17).

   o  A non-critical extKeyUsage containing id-kp-codeSigning and id-kp-
      OCSPSigning is encoded as the CBOR int 3 8 followed by the CBOR
      array [ 3, 6 ].

   o  A non-critical subjectAltName containing only the dNSName
      example.com is encoded as the CBOR int 4 3 followed by the CBOR text
      string "example.com".

   Thus, the extension field of a certificate containing all of the
   above extensions in the given order would be encoded as the CBOR
   array [ -1, -4, -1, 2, 17, 3, 8, [ 3, 6 ], 4, 3, "example.com" ].

4.  Compliance Requirements for Constrained IoT

   For general purpose applications, the normative requirements of
   [RFC5280] applies.  This section describes the mandatory to implement
   algorithms and OIDs for constrained IoT application; the values of
   the OIDs including certificate fields and extensions, time format,
   attributes in distinguished names, etc.

   TODO: Write this section

5.  Legacy Considerations

   C509 certificates can be deployed with legacy X.509 certificates and
   CA infrastructure.  In order to verify the signature, the C509
   certificate is used to recreate the original X.509 data structure to
   be able to verify the signature.

   For protocols like TLS/DTLS 1.2, where the handshake is sent
   unencrypted, the actual encoding and compression can be done at
   different locations depending on the deployment setting.  For
   example, the mapping between C509 certificate and standard X.509
   certificate can take place in a 6LoWPAN border gateway which allows
   the server side to stay unmodified.  This case gives the advantage of
   the low overhead of a C509 certificate over a constrained wireless
   links.  The conversion to X.509 within an IoT device will incur a
   computational overhead, however, measured in energy this is likely to
   be negligible compared to the reduced communication overhead.

   For the setting with constrained server and server-only
   authentication, the server only needs to be provisioned with the C509
   certificate and does not perform the conversion to X.509.  This
   option is viable when client authentication can be asserted by other
   means.

   For protocols like IKEv2, TLS/DTLS 1.3, and EDHOC, where certificates
   are encrypted, the proposed encoding needs to be done fully end-to-
   end, through adding the encoding/decoding functionality to the
   server.

6.  Expected Certificate Sizes

   The CBOR encoding of the sample certificate chains given in
   Appendix A results in the numbers shown in Figure 2. 2 and Figure 3.
   After [RFC7925] profiling, most duplicated information has been
   removed, and the remaining text strings are minimal in size.
   Therefore, the further size reduction reached with general
   compression mechanisms such as Brotli will be small, mainly
   corresponding to making the ASN.1 encoding more compact.  CBOR
   encoding can however significantly compress RFC 7925 profiled
   certificates.  For the example HTTPS certificate chains (www.ietf.org
   and tools.ietf.org) both C509 and Brotli perform well complementing
   each other.  C509 use dedicated information to compress individual
   certificates, while Brotli can compress duplicate information in the
   entire chain.  For Brtoli Brotli [RFC7932], the brotli command line tool 1.09 Rust crate Brotli 3.3.0 was
   used with the
   default best compression level.

   +------------------+--------------+------------+--------------------+ level 11 and window size 22.

     +---------------------------------------+-----------+-----------+
     |                                       | COSE_X509 | COSE_C509 |
     +---------------------------------------+-----------+-----------+
     | RFC 7925 profiled IoT Certificate     |   Brotli       317 |  C509 Certificate       139 |
   +------------------+---------------------------+--------------------+
     +---------------------------------------+-----------+-----------+
     | ECDSA HTTPS Certificate Size Chain         |     314      2193 |     303      1394 |         138
     +---------------------------------------+-----------+-----------+
     | RSA HTTPS Certificate Chain           |      5175 |      3934 |
   +------------------+--------------+------------+--------------------+
     +---------------------------------------+-----------+-----------+

      Figure 2: Comparing Sizes of Certificates Certificate Chains in COSE (bytes)

    +-------------------+------+---------------+------+---------------+
    |                   | X509 | X509 + Brotli | C509 | C509 + Brotli |
    +-------------------+------+---------------+------+---------------+
    | RFC 7925 Cert     |  327 |           324 |  151 |           167 |
    +-------------------+------+---------------+------+---------------+
    | ECDSA HTTPS Chain | 2204 |          1455 | 1409 |          1058 |
    +-------------------+------+---------------+------+---------------+
    | RSA HTTPS Chain   | 5190 |          3244 | 3957 |          2841 |
    +-------------------+------+---------------+------+---------------+

        Figure 3: Comparing Sizes of Certificate Chains TLS (bytes)

7.  Security Considerations

   The CBOR profiling of X.509 certificates does not change the security
   assumptions needed when deploying standard X.509 certificates but
   decreases the number of fields transmitted, which reduces the risk
   for implementation errors.

   The use of natively signed C509 certificates removes the need for
   ASN.1 encoding, which is a rich source of security vulnerabilities.

   Conversion between the certificate formats can be made in constant
   time to reduce risk of information leakage through side channels.

   The mechanism in this draft does not reveal any additional
   information compared to X.509.  Because of difference in size, it
   will be possible to detect that this profile is used.  The gateway
   solution described in Section 5 requires unencrypted certificates and
   is not recommended.

8.  IANA Considerations

   This document creates several new registries under the new heading
   "C509 Certificate".  For all items, the 'Reference' field points to
   this document.

   The expert reviewers for the registries defined in this document are
   expected to ensure that the usage solves a valid use case that could
   not be solved better in a different way, that it is not going to
   duplicate one that is already registered, and that the registered
   point is likely to be used in deployments.  They are furthermore
   expected to check the clarity of purpose and use of the requested
   code points.  Experts should take into account the expected usage of
   entries when approving point assignment, and the length of the
   encoded value should be weighed against the number of code points
   left that encode to that size and how constrained the systems it will
   be used on are.  Values in the interval [-24, 23] have a 1 byte
   encodings, other values in the interval [-256, 255] have a 2 byte
   encodings, and the remaining values in the interval [-65536, 65535]
   have 3 byte encodings.

8.1.  C509 Certificate Types Registry

   IANA has created a new registry titled "C509 Certificate Types" under
   the new heading "C509 Certificate".  The columns of the registry are
   Value, Description, and Reference, where Value is an integer, and the
   other columns are text strings.  For values in the interval [-24, 23]
   the registration procedure is "IETF Review" and "Expert Review".  For
   all other values the registration procedure is "Expert Review".  The
   initial contents of the registry are:

   +-------+-----------------------------------------------------------+
   | Value | Description                                               |
   +=======+===========================================================+
   |     0 | Natively Signed C509 Certificate following X.509 v3       |
   +-------+-----------------------------------------------------------+
   |     1 | CBOR re-encoding of X.509 v3 Certificate                  |
   +-------+-----------------------------------------------------------+

                     Figure 3: 4: C509 Certificate Types

8.2.  C509 Certificate Attributes Registry

   IANA has created a new registry titled "C509 Certificate Attributes"
   under the new heading "C509 Certificate".  The columns of the
   registry are Value, Name, OID, DER, Comments, and Reference, where
   Value is an positive integer, and the other columns are text strings.  Only
   non-negative values can be registered.
   For values in the interval

   [0, [1, 23] the registration procedure is
   "IETF Review" and "Expert Review".  For all other values the
   registration procedure is "Expert Review".  The initial contents of
   the registry are:

   +-------+-----------------------------------------------------------+
   | Value | Attribute                                                 |
   +=======+===========================================================+
   |     1 | Name:            Common Name                              |
   |       | OID:             2.5.4.3                                  |
   |       | DER:             06 03 55 04 03                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     2 | Name:            Surname                                  |
   |       | OID:             2.5.4.4                                  |
   |       | DER:             06 03 55 04 04                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     3 | Name:            Serial Number                            |
   |       | OID:             2.5.4.5                                  |
   |       | DER:             06 03 55 04 05                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     4 | Name:            Country                                  |
   |       | OID:             2.5.4.6                                  |
   |       | DER:             06 03 55 04 06                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     5 | Name:            Locality                                 |
   |       | OID:             2.5.4.7                                  |
   |       | DER:             06 03 55 04 07                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     6 | Name:            State or Province                        |
   |       | OID:             2.5.4.8                                  |
   |       | DER:             06 03 55 04 08                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     7 | Name:            Street Address                           |
   |       | OID:             2.5.4.9                                  |
   |       | DER:             06 03 55 04 09                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     8 | Name:            Organization                             |
   |       | OID:             2.5.4.10                                 |
   |       | DER:             06 03 55 04 0A                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     9 | Name:            Organizational Unit                      |
   |       | OID:             2.5.4.11                                 |
   |       | DER:             06 03 55 04 0B                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    10 | Name:            Title                                    |
   |       | OID:             2.5.4.12                                 |
   |       | DER:             06 03 55 04 0C                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    11 | Name:            Postal Code                              |
   |       | OID:             2.5.4.17                                 |
   |       | DER:             06 03 55 04 11                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    12 | Name:            Given Name                               |
   |       | OID:             2.5.4.42                                 |
   |       | DER:             06 03 55 04 2A                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    13 | Name:            Initials                                 |
   |       | OID:             2.5.4.43                                 |
   |       | DER:             06 03 55 04 2B                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    14 | Name:            Generation Qualifier                     |
   |       | OID:             2.5.4.44                                 |
   |       | DER:             06 03 55 04 2C                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    15 | Name:            DN Qualifier                             |
   |       | OID:             2.5.4.46                                 |
   |       | DER:             06 03 55 04 2E                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    16 | Name:            Pseudonym                                |
   |       | OID:             2.5.4.65                                 |
   |       | DER:             06 03 55 04 41                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    17 | Name:            Organization Identifier                  |
   |       | OID:             2.5.4.97                                 |
   |       | DER:             06 03 55 04 61                           |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+

                   Figure 4: 5: C509 Certificate Attributes

8.3.  C509 Certificate Extensions Registry

   IANA has created a new registry titled "C509 Certificate Extensions"
   under the new heading "C509 Certificate".  The columns of the
   registry are Value, Name, OID, DER, Comments, extensionValue, and
   Reference, where Value is an positive integer, and the other columns
   are text strings.  Only non-negative values can be registered.  For values in the interval [0, [1, 23] the
   registration procedure is "IETF Review" and "Expert Review".  For all
   other values the registration procedure is "Expert Review".  The
   initial contents of the registry are:

 +-------+-----------------------------------------------------------+
 | Value | Extension                                                 |
 +=======+===========================================================+
 |     0     1 | Name:            Subject Key Identifier                   |
 |       | OID:             2.5.29.14                                |
 |       | DER:             06 03 55 1D 0E                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |     1     2 | Name:            Key Usage                                |
 |       | OID:             2.5.29.15                                |
 |       | DER:             06 03 55 1D 0F                           |
 |       | Comments:                                                 |
 |       | AttributeValue:  int                                      |
 +-------+-----------------------------------------------------------+
 |     2     3 | Name:            Subject Alternative Name                 |
 |       | OID:             2.5.29.17                                |
 |       | DER:             06 03 55 1D 11                           |
 |       | Comments:                                                 |
 |       | extensionValue:  [ + ( int, any ) ] / text  ExtValueSAN                              |
 +-------+-----------------------------------------------------------+
 |     3     4 | Name:            Basic Constraints                        |
 |       | OID:             2.5.29.19                                |
 |       | DER:             06 03 55 1D 13                           |
 |       | Comments:                                                 |
 |       | extensionValue:  int                                      |
   +-------+-----------------------------------------------------------+
 +-------+------------------------------------------er-----------------+
 |     4     5 | Name:            CRL Distribution Points                  |
 |       | OID:             2.5.29.31                                |
 |       | DER:             06 03 55 1D 1F                           |
 |       | Comments:                                                 |
 |       | extensionValue:  [ + ( int, any ) ] / text  ExtValueCDP                              |
 +-------+-----------------------------------------------------------+
 |     5     6 | Name:            Certificate Policies                     |
 |       | OID:             2.5.29.32                                |
 |       | DER:             06 03 55 1D 20                           |
 |       | Comments:                                                 |
 |       | extensionValue:  [ + ( oid, ? text ) ]  ExtValueCP                               |
 +-------+-----------------------------------------------------------+
 |     6     7 | Name:            Authority Key Identifier                 |
 |       | OID:             2.5.29.35                                |
 |       | DER:             06 03 55 1D 23                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes  ExtValueAKI                              |
 +-------+-----------------------------------------------------------+
 |     7     8 | Name:            Extended Key Usage                       |
 |       | OID:             2.5.29.37                                |
 |       | DER:             06 03 55 1D 25                           |
 |       | Comments:                                                 |
 |       | extensionValue:  int  ExtValueEKU                              |
 +-------+-----------------------------------------------------------+
 |     8     9 | Name:            Authority Information Access             |
 |       | OID:             1.3.6.1.5.5.7.1.1                        |
 |       | DER:             06 08 2B 06 01 05 05 07 01 01            |
 |       | Comments:                                                 |
 |       | extensionValue:  [ + ( 1 / 2 , text ) ]  ExtValueAIA                              |
 +-------+-----------------------------------------------------------+
 |     9    10 | Name:            Signed Certificate Timestamp List        |
 |       | OID:             1.3.6.1.4.1.11129.2.4.2                  |
 |       | DER:             06 0A 2B 06 01 04 01 D6 79 02 04 02      |
 |       | Comments:                                                 |
 |       | extensionValue:  [ bytes, ~biguint,                       |
   |       |                    AlgorithmIdentifier, bytes]  ExtValueSCT                             |
 +-------+-----------------------------------------------------------+
 |    24 | Name:            Subject Directory Attributes             |
 |       | OID:             2.5.29.9                                 |
 |       | DER:             06 03 55 1D 09                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    25 | Name:            Issuer Alternative Name                  |
 |       | OID:             2.5.29.18                                |
 |       | DER:             06 03 55 1D 12                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    26 | Name:            Name Constraints                         |
 |       | OID:             2.5.29.30                                |
 |       | DER:             06 03 55 1D 1E                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    27 | Name:            Policy Mappings                          |
 |       | OID:             2.5.29.33                                |
 |       | DER:             06 03 55 1D 21                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    28 | Name:            Policy Constraints                       |
 |       | OID:             2.5.29.36                                |
 |       | DER:             06 03 55 1D 24                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    29 | Name:            Freshest CRL                             |
 |       | OID:             2.5.29.46                                |
 |       | DER:             06 03 55 1D 2E                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    30 | Name:            Inhibit anyPolicy                        |
 |       | OID:             2.5.29.54                                |
 |       | DER:             06 03 55 1D 36                           |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+
 |    31 | Name:            Subject Information Access               |
 |       | OID:             1.3.6.1.5.5.7.1.11                       |
 |       | DER:             06 08 2B 06 01 05 05 07 01 0B            |
 |       | Comments:                                                 |
 |       | extensionValue:  bytes                                    |
 +-------+-----------------------------------------------------------+

                   Figure 6: C509 Certificate Extensions

8.4.  C509 Certificate Certificate Policies Registry

   IANA has created a new registry titled "C509 Certificate Certificate
   Policies" under the new heading "C509 Certificate".  The columns of
   the registry are Value, Name, OID, DER, Comments, and Reference,
   where Value is an integer, and the other columns are text strings.
   For values in the interval [-24, 23] the registration procedure is
   "IETF Review" and "Expert Review".  For all other values the
   registration procedure is "Expert Review".  The initial contents of
   the registry are:

   +-------+-----------------------------------------------------------+
   | Value | Certificate Policy                                        |
   +-------+-----------------------------------------------------------+
   +=======+===========================================================+
   |    28     1 | Name:            Policy Constraints            Domain Validation (DV)                   |
   |       | OID:             2.5.29.36             2.23.140.1.2.1                           |
   |       | DER:             06 03 55 1D 24 06 67 81 0C 01 02 01                  |
   |       | Comments:                                                 |
   |       | extensionValue:  bytes                                    |
   +-------+-----------------------------------------------------------+
   |    29     2 | Name:            Freshest CRL            Organization Validation (OV)             |
   |       | OID:             2.5.29.46             2.23.140.1.2.2                           |
   |       | DER:             06 03 55 1D 2E 06 67 81 0C 01 02 02                  |
   |       | Comments:                                                 |
   |       | extensionValue:  bytes                                    |
   +-------+-----------------------------------------------------------+
   |    30     3 | Name:            Inhibit anyPolicy            Individual Validation (IV)               |
   |       | OID:             2.5.29.54             2.23.140.1.2.3                           |
   |       | DER:             06 06 67 81 0C 01 02 03 55 1D 36                  |
   |       | Comments:                                                 |
   |       | extensionValue:  bytes                                    |
   +-------+-----------------------------------------------------------+
   |    31     4 | Name:            Subject Information Access            Extended Validation (EV)                 |
   |       | OID:             1.3.6.1.5.5.7.1.11             2.23.140.1.1                             |
   |       | DER:             06 08 2B 06 01 05 05 07 67 81 0C 01 01 0B                     |
   |       | Comments:                                                 |
   |       | extensionValue:  bytes                                    |
   +-------+-----------------------------------------------------------+

              Figure 5: 7: C509 Certificate Extensions

8.4. Certificate Policies

8.5.  C509 Certificate Extended Key Usages Registry

   IANA has created a new registry titled "C509 Certificate Extended Key
   Usages" under the new heading "C509 Certificate".  The columns of the
   registry are Value, Name, OID, DER, Comments, and Reference, where
   Value is an integer, and the other columns are text strings.  For
   values in the interval [-24, 23] the registration procedure is "IETF
   Review" and "Expert Review".  For all other values the registration
   procedure is "Expert Review".  The initial contents of the registry
   are:

   +-------+-----------------------------------------------------------+
   | Value | Extended Key Usage                                        |
   +=======+===========================================================+
   |     1 | Name:            TLS Server authentication                |
   |       | OID:             1.3.6.1.5.5.7.3.1                        |
   |       | DER:             06 08 2B 06 01 05 05 07 03 01            |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     2 | Name:            TLS Client Authentication                |
   |       | OID:             1.3.6.1.5.5.7.3.2                        |
   |       | DER:             06 08 2B 06 01 05 05 07 03 02            |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     3 | Name:            Code Signing                             |
   |       | OID:             1.3.6.1.5.5.7.3.3                        |
   |       | DER:             06 08 2B 06 01 05 05 07 03 03            |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     4 | Name:            Email protection (S/MIME)                |
   |       | OID:             1.3.6.1.5.5.7.3.4                        |
   |       | DER:             06 08 2B 06 01 05 05 07 03 04            |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     8 | Name:            Time Stamping                            |
   |       | OID:             1.3.6.1.5.5.7.3.8                        |
   |       | DER:             06 08 2B 06 01 05 05 07 03 08            |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |     9 | Name:            OCSP Signing                             |
   |       | OID:             1.3.6.1.5.5.7.3.9                        |
   |       | DER:             06 08 2B 06 01 05 05 07 03 09            |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+

              Figure 6: 8: C509 Certificate Extended Key Usages

8.5.

8.6.  C509 Certificate General Names Registry

   IANA has created a new registry titled "C509 Certificate General
   Names" under the new heading "C509 Certificate".  The columns of the
   registry are Value, General Name, and Reference, where Value is an
   integer, and the other columns are text strings.  For values in the
   interval [-24, 23] the registration procedure is "IETF Review" and
   "Expert Review".  For all other values the registration procedure is
   "Expert Review".  The initial contents of the registry are:

   +-------+-----------------------------------------------------------+
   | Value | General Names                                             |
   +=======+===========================================================+
   |    -1 | Name:            otherName with hardwareModuleName        |
   |       | Comments:                                                 |
   |       | Value:           [ ~oid, bytes ]                          |
   +-------+-----------------------------------------------------------+
   |     0 | Name:            otherName                                |
   |       | Comments:                                                 |
   |       | Value:           [ ~oid, bytes ]                          |
   +-------+-----------------------------------------------------------+
   |     1 | Name:            rfc822Name                               |
   |       | Comments:                                                 |
   |       | Value:           text                                     |
   +-------+-----------------------------------------------------------+
   |     2 | Name:            dNSName                                  |
   |       | Comments:                                                 |
   |       | Value:           text                                     |
   +-------+-----------------------------------------------------------+
   |     4 | Name:            directoryName                            |
   |       | Comments:                                                 |
   |       | Value:           Name                                     |
   +-------+-----------------------------------------------------------+
   |     6 | Name:            uniformResourceIdentifier                |
   |       | Comments:                                                 |
   |       | Value:           text                                     |
   +-------+-----------------------------------------------------------+
   |     7 | Name:            iPAddress                                |
   |       | Comments:                                                 |
   |       | Value:           bytes                                    |
   +-------+-----------------------------------------------------------+
   |     8 | Name:            registeredID                             |
   |       | Comments:                                                 |
   |       | Value:           ~oid                                     |
   +-------+-----------------------------------------------------------+

                 Figure 7: 9: C509 Certificate General Names

8.6.

8.7.  C509 Certificate Signature Algorithms Registry

   IANA has created a new registry titled "C509 Certificate Signature
   Algorithms" under the new heading "C509 Certificate".  The columns of
   the registry are Value, Name, OID, Parameters, DER, Comments, and
   Reference, where Value is an integer, and the other columns are text
   strings.  For values in the interval [-24, 23] the registration
   procedure is "IETF Review" and "Expert Review".  For all other values
   the registration procedure is "Expert Review".  The initial contents
   of the registry are:

   +-------+-----------------------------------------------------------+
   | Value | X.509 Signature Algorithms                                |
   +=======+===========================================================+
   |  -256 | Name:        RSASSA-PKCS1-v1_5 with SHA-1                 |
   |       | OID:         1.2.840.113549.1.1.5                         |
   |       | Parameters:  NULL                                         |
   |       | DER:         30 0D 06 09 2A 86 48 86 F7 0D 01 01 05 05 00 |
   |       | Comments:    Don't use                                    |
   +-------+-----------------------------------------------------------+
   |  -255 | Name:        ECDSA with SHA-1                             |
   |       | OID:         1.2.840.10045.4.1                            |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 09 06 07 2A 86 48 CE 3D 04 01             |
   |       | Comments:    Don't use. Compressed signature value        |
   +-------+-----------------------------------------------------------+
   |     0 | Name:        ECDSA with SHA-256                           |
   |       | OID:         1.2.840.10045.4.3.2                          |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2A 86 48 CE 3D 04 03 02          |
   |       | Comments:    Compressed signature value                   |
   +-------+-----------------------------------------------------------+
   |     1 | Name:        ECDSA with SHA-384                           |
   |       | OID:         1.2.840.10045.4.3.3                          |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2A 86 48 CE 3D 04 03 03          |
   |       | Comments:    Compressed signature value                   |
   +-------+-----------------------------------------------------------+
   |     2 | Name:        ECDSA with SHA-512                           |
   |       | OID:         1.2.840.10045.4.3.4                          |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2A 86 48 CE 3D 04 03 04          |
   |       | Comments:    Compressed signature value                   |
   +-------+-----------------------------------------------------------+
   |     3 | Name:        ECDSA with SHAKE128                          |
   |       | OID:         1.3.6.1.5.5.7.6.32                           |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2B 06 01 05 05 07 06 20          |
   |       | Comments:    Compressed signature value                   |
   +-------+-----------------------------------------------------------+
   |     4 | Name:        ECDSA with SHAKE256                          |
   |       | OID:         1.3.6.1.5.5.7.6.33                           |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2B 06 01 05 05 07 06 21          |
   |       | Comments:    Compressed signature value                   |
   +-------+-----------------------------------------------------------+
   |    12 | Name:        Ed25519                                      |
   |       | OID:         1.3.101.112                                  |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 05 06 03 2B 65 70                         |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    13 | Name:        Ed448                                        |
   |       | OID:         1.3.101.113                                  |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 05 06 03 2B 65 71                         |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    23 | Name:        RSASSA-PKCS1-v1_5 with SHA-256               |
   |       | OID:         1.2.840.113549.1.1.11                        |
   |       | Parameters:  NULL                                         |
   |       | DER:         30 0B 06 09 2A 86 48 86 F7 0D 01 01 0B 05 00 |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    24 | Name:        RSASSA-PKCS1-v1_5 with SHA-384               |
   |       | OID:         1.2.840.113549.1.1.12                        |
   |       | Parameters:  NULL                                         |
   |       | DER:         30 0B 06 09 2A 86 48 86 F7 0D 01 01 0C 05 00 |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    25 | Name:        RSASSA-PKCS1-v1_5 with SHA-512               |
   |       | OID:         1.2.840.113549.1.1.13                        |
   |       | Parameters:  NULL                                         |
   |       | DER:         30 0B 06 09 2A 86 48 86 F7 0D 01 01 0D 05 00 |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    26 | Name:        RSASSA-PSS with SHA-256                      |
   |       | OID:         1.2.840.113549.1.1.10                        |
   |       | Parameters:  SHA-256, MGF-1 with SHA-256, saltLength = 32 |
   |       | DER:         30 41 06 09 2A 86 48 86 F7 0D 01 01 0A 30 34 |
   |       |              A0 0F 30 0D 06 09 60 86 48 01 65 03 04 02 01 |
   |       |              05 00 A1 1C 30 1A 06 09 2A 86 48 86 F7 0D 01 |
   |       |              01 08 30 0D 06 09 60 86 48 01 65 03 04 02 01 |
   |       |              05 00 a2 03 02 01 20                         |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    27 | Name:        RSASSA-PSS with SHA-384                      |
   |       | OID:         1.2.840.113549.1.1.10                        |
   |       | Parameters:  SHA-384, MGF-1 with SHA-384, saltLength = 48 |
   |       | DER:         30 41 06 09 2A 86 48 86 F7 0D 01 01 0A 30 34 |
   |       |              A0 0F 30 0D 06 09 60 86 48 01 65 03 04 02 02 |
   |       |              05 00 A1 1C 30 1A 06 09 2A 86 48 86 F7 0D 01 |
   |       |              01 08 30 0D 06 09 60 86 48 01 65 03 04 02 02 |
   |       |              05 00 A2 03 02 01 30                         |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    28 | Name:        RSASSA-PSS with SHA-512                      |
   |       | OID:         1.2.840.113549.1.1.10                        |
   |       | Parameters:  SHA-512, MGF-1 with SHA-512, saltLength = 64 |
   |       | DER:         30 41 06 09 2A 86 48 86 F7 0D 01 01 0A 30 34 |
   |       |              A0 0F 30 0D 06 09 60 86 48 01 65 03 04 02 03 |
   |       |              05 00 A1 1C 30 1A 06 09 2A 86 48 86 F7 0D 01 |
   |       |              01 08 30 0D 06 09 60 86 48 01 65 03 04 02 03 |
   |       |              05 00 A2 03 02 01 40                         |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    29 | Name:        RSASSA-PSS with SHAKE128                     |
   |       | OID:         1.3.6.1.5.5.7.6.30                           |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2B 06 01 05 05 07 06 1E          |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    30 | Name:        RSASSA-PSS with SHAKE256                     |
   |       | OID:         1.3.6.1.5.5.7.6.31                           |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0A 06 08 2B 06 01 05 05 07 06 1F          |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    42 | Name:        HSS / LMS                                    |
   |       | OID:         1.2.840.113549.1.9.16.3.17                   |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0D 06 0B 2A 86 48 86 F7 0D 01 09 10 03 11 |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    43 | Name:        XMSS                                         |
   |       | OID:         0.4.0.127.0.15.1.1.13.0                      |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0B 06 09 04 00 7F 00 0F 01 01 0D 00       |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+
   |    44 | Name:        XMSS^MT                                      |
   |       | OID:         0.4.0.127.0.15.1.1.14.0                      |
   |       | Parameters:  Absent                                       |
   |       | DER:         30 0B 06 09 04 00 7F 00 0F 01 01 0E 00       |
   |       | Comments:                                                 |
   +-------+-----------------------------------------------------------+

             Figure 8: 10: C509 Certificate Signature Algorithms

8.7.

8.8.  C509 Certificate Public Key Algorithms Registry

   IANA has created a new registry titled "C509 Certificate Public Key
   Algorithms" under the new heading "C509 Certificate".  The columns of
   the registry are Value, Name, OID, Parameters, DER, Comments, and
   Reference, where Value is an integer, and the other columns are text
   strings.  For values in the interval [-24, 23] the registration
   procedure is "IETF Review" and "Expert Review".  For all other values
   the registration procedure is "Expert Review".  T The initial
   contents of the registry are:

  +-------+-----------------------------------------------------------+
  | Value | X.509 Public Key Algorithms                               |
  +=======+===========================================================+
  |     0 | Name:        RSA                                          |
  |       | OID:         1.2.840.113549.1.1.1                         |
  |       | Parameters:  NULL                                         |
  |       | DER:         30 0d 06 09 2a 86 48 86 f7 0d 01 01 01 05 00 |
  |       | Comments:    Compressed subjectPublicKey                  |
  +-------+-----------------------------------------------------------+
  |     1 | Name:        EC Public Key (Weierstrass) with secp256r1    |
  |       | OID:         1.2.840.10045.2.1                            |
  |       | Parameters:  namedCurve = secp256r1 (1.2.840.10045.3.1.7) |
  |       | DER:         30 13 06 07 2A 86 48 CE 3D 02 01 06 08 2A 86 |
  |       |              48 CE 3D 03 01 07                            |
  |       | Comments:    Point compressed subjectPublicKey            |
  +-------+-----------------------------------------------------------+
  |     2 | Name:        EC Public Key (Weierstrass) with secp384r1    |
  |       | OID:         1.2.840.10045.2.1                            |
  |       | Parameters:  namedCurve = secp384r1 (1.3.132.0.34)        |
  |       | DER:         30 10 06 07 2A 86 48 CE 3D 02 01 06 05 2B 81 |
  |       |              04 00 22                                     |
  |       | Comments:    Point compressed subjectPublicKey            |
  +-------+-----------------------------------------------------------+
  |     3 | Name:        EC Public Key (Weierstrass) with secp521r1    |
  |       | OID:         1.2.840.10045.2.1                            |
  |       | Parameters:  namedCurve = secp521r1 (1.3.132.0.35)        |
  |       | DER:         30 10 06 07 2A 86 48 CE 3D 02 01 06 05 2B 81 |
  |       |              04 00 23                                     |
  |       | Comments:    Point compressed subjectPublicKey            |
  +-------+-----------------------------------------------------------+
  |     8 | Name:        X25519 (Montgomery)                          |
  |       | OID:         1.3.101.110                                  |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 05 06 03 2B 65 6E                         |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+
  |     9 | Name:        X448 (Montgomery)                            |
  |       | OID:         1.3.101.111                                  |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 05 06 03 2B 65 6F                         |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+
  |    10 | Name:        Ed25519 (Twisted Edwards)                    |
  |       | OID:         1.3.101.112                                  |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 05 06 03 2B 65 70                         |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+
  |    11 | Name:        Ed448 (Edwards)                              |
  |       | OID:         1.3.101.113                                  |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 05 06 03 2B 65 71                         |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+
  |    16 | Name:        HSS / LMS                                    |
  |       | OID:         1.2.840.113549.1.9.16.3.17                   |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 0D 06 0B 2A 86 48 86 F7 0D 01 09 10 03 11 |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+
  |    17 | Name:        XMSS                                         |
  |       | OID:         0.4.0.127.0.15.1.1.13.0                      |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 0B 06 09 04 00 7F 00 0F 01 01 0D 00       |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+
  |    18 | Name:        XMSS^MT                                      |
  |       | OID:         0.4.0.127.0.15.1.1.14.0                      |
  |       | Parameters:  Absent                                       |
  |       | DER:         30 0B 06 09 04 00 7F 00 0F 01 01 0E 00       |
  |       | Comments:                                                 |
  +-------+-----------------------------------------------------------+

             Figure 9: 11: C509 Certificate Public Key Algorithms

8.8.

8.9.  COSE Header Parameters Registry

   EDITORS NOTE: Should x5u refer to a bag or a chain? The text should be moved a section and not be in the
   IANA Section.

   This document registers the following entries in the "COSE Header
   Parameters" registry under the "CBOR Object Signing and Encryption
   (COSE)" heading.  The formatting and processing for c5b, c5c, and
   c5t, and c5u are similar to x5bag, x5chain, x5t, x5u defined in
   [I-D.ietf-cose-x509] except that the certificates are CBOR encoded C509 instead of
   DER encoded, encoded X.509 and uses a COSE_C5 COSE_C509 structure instead of
   COSE_X509, and that c5t MUST refer to an end-entity certificate.
   COSE_X509. c5u provides an alternative way to identify an untrusted
   certificate bag/
   chain bag/chain by reference with a URI.  The content is a COSE_C5
   COSE_C509 item served with the application/cbor content format.  The COSE_C5
   COSE_C509 structure used in c5b, c5c, and c5u is defined as:

   COSE_C5

   COSE_C509 = C509Certificate / [ + CBORCertificate 2* C509Certificate ]

   As the contents of c5bag, c5chain, c5t, and c5u are untrusted input,
   the header parameters can be in either the protected or unprotected
   header bucket.  The trust mechanism MUST process any certificates in
   the c5b, c5c, and c5u parameters as untrusted input.  The presence of
   a self-signed certificate in the parameter MUST NOT cause the update
   of the set of trust anchors without some out-of-band confirmation.

   Note that certificates can also be identified with a 'kid' header
   parameter by storing 'kid' and the associated bag or chain in a
   dictionary.

   +-----------+-------+----------------+------------------------------+
   | Name      | Label | Value Type     | Description                  |
   +===========+=======+================+==============================+
   | c5b       |  TBD1 | COSE_C5 COSE_C509      | An unordered bag of C509     |
   |           |       |                | certificates                 |
   +-----------+-------+----------------+------------------------------+
   | c5c       |  TBD2 | COSE_C5 COSE_C509      | An ordered chain of C509     |
   |           |       |                | certificates                 |
   +-----------+-------+----------------+------------------------------+
   | c5t       |  TBD3 | COSE_CertHash  | Hash of a C509 certificate C509Certificate    |
   +-----------+-------+----------------+------------------------------+
   | c5u       |  TBD4 | uri            | URI pointing to a COSE_C5 COSE_C509  |
   |           |       |                | containing a ordered chain   |
   |           |       |                | of certificates              |
   +-----------+-------+----------------+------------------------------+

8.9.

8.10.  TLS Certificate Types Registry

   This document registers the following entry in the "TLS Certificate
   Types" registry under the "Transport Layer Security (TLS) Extensions"
   heading.  The new certificate type can be used with additional TLS
   certificate compression [RFC8879].  C509 is defined in the same way
   as as X509, but uses a different value and instead of DER-encoded
   X.509 certificate, opaque cert_data<1..2^24-1> contains a the CBOR
   sequence ~C509Certificate (an unwrapped C509Certificate).

   EDITOR'S NOTE: The TLS registrations should be discussed and approved
   by the TLS WG at a later stage.  When COSE WG has adopted work on
   C509 certificates, it could perhaps be presented in the TLS WG.  The
   TLS WG might e.g. want a separate draft in the TLS WG.

   +-------+------------------+-------------+--------------------------+
   | Value | Name             | Recommended | Comment                  |
   +=======+==================+=============+==========================+
   |  TBD5 | C509 Certificate |           Y |                          |
   +-------+------------------+-------------+--------------------------+

8.10.

8.11.  CBOR Tags Registry

   This document registers the following entries in the "CBOR Tags"
   registry under the "Concise Binary Object Representation (CBOR) Tags"
   heading.

   +------+------------------------------------------------------------+
   |  Tag | X.509 Public Key Algorithms                                |
   +======+============================================================+
   | TDB6 | Data Item: COSE_C5 COSE_C509                                       |
   |      | Semantics: An ordered chain of C509 certificates           |
   |      | Reference: This document                                   |
   +------+------------------------------------------------------------+

9.  References

9.1.  Normative References

   [I-D.ietf-cbor-tags-oid]
              Bormann, C., "Concise Binary Object Representation (CBOR)
              Tags for Object Identifiers", draft-ietf-cbor-tags-oid-06
              (work in progress), March 2021.

   [I-D.ietf-cose-x509]
              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header parameters for carrying and referencing X.509
              certificates", draft-ietf-cose-x509-08 (work in progress),
              December 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4108]  Housley, R., "Using Cryptographic Message Syntax (CMS) to
              Protect Firmware Packages", RFC 4108,
              DOI 10.17487/RFC4108, August 2005,
              <https://www.rfc-editor.org/info/rfc4108>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8742]  Bormann, C., "Concise Binary Object Representation (CBOR)
              Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
              <https://www.rfc-editor.org/info/rfc8742>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/info/rfc8949>.

   [SECG]     "Elliptic Curve Cryptography, Standards for Efficient
              Cryptography Group, ver. 2", 2009,
              <https://secg.org/sec1-v2.pdf>.

9.2.  Informative References

   [CAB-Baseline]
              CA/Browser Forum, ., "CA/Browser Forum, "Baseline
              Requirements for the Issuance and Management of Publicly-
              Trusted Certificates Version 1.7.3", October 2020,
              <https://cabforum.org/baseline-requirements-documents/>.

   [CborMe]   Bormann, C., "CBOR Playground", May 2018,
              <http://cbor.me/>.

   [I-D.ietf-emu-eap-tls13]
              Mattsson, J. and M. Sethi, "Using EAP-TLS with TLS 1.3",
              draft-ietf-emu-eap-tls13-14
              draft-ietf-emu-eap-tls13-15 (work in progress), February May 2021.

   [I-D.ietf-emu-eaptlscert]
              Sethi, M., Mattsson, J., and S. Turner, "Handling Large
              Certificates and Long Certificate Chains in TLS-based EAP
              Methods", draft-ietf-emu-eaptlscert-08 (work in progress),
              November 2020.

   [I-D.ietf-lake-edhoc]
              Selander, G., Mattsson, J., J. P., and F. Palombini,
              "Ephemeral Diffie-Hellman Over COSE (EDHOC)", draft-ietf-lake-
              edhoc-06 draft-ietf-
              lake-edhoc-06 (work in progress), April 2021.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-34 (work
              in progress), January 2021.

   [I-D.ietf-tls-ctls]
              Rescorla, E., Barnes, R., and H. Tschofenig, "Compact TLS
              1.3", draft-ietf-tls-ctls-01 (work in progress), November
              2020.

   [I-D.ietf-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-40 draft-ietf-tls-dtls13-43 (work in progress), January April
              2021.

   [I-D.ietf-uta-tls13-iot-profile]
              Tschofenig, H. and T. Fossati, "TLS/DTLS 1.3 Profiles for
              the Internet of Things", draft-ietf-uta-tls13-iot-
              profile-01 (work in progress), February 2021.

   [IEEE-802.1AR]
              Institute of Electrical and Electronics Engineers, .,
              "IEEE Standard for Local and metropolitan area networks-
              Secure Device Identity", IEEE Standard 802.1AR-2018 ,
              August 2018,
              <https://standards.ieee.org/standard/802_1AR-2018.html>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [RFC7925]  Tschofenig, H., Ed. and T. Fossati, "Transport Layer
              Security (TLS) / Datagram Transport Layer Security (DTLS)
              Profiles for the Internet of Things", RFC 7925,
              DOI 10.17487/RFC7925, July 2016,
              <https://www.rfc-editor.org/info/rfc7925>.

   [RFC7932]  Alakuijala, J. and Z. Szabadka, "Brotli Compressed Data
              Format", RFC 7932, DOI 10.17487/RFC7932, July 2016,
              <https://www.rfc-editor.org/info/rfc7932>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8603]  Jenkins, M. and L. Zieglar, "Commercial National Security
              Algorithm (CNSA) Suite Certificate and Certificate
              Revocation List (CRL) Profile", RFC 8603,
              DOI 10.17487/RFC8603, May 2019,
              <https://www.rfc-editor.org/info/rfc8603>.

   [RFC8879]  Ghedini, A. and V. Vasiliev, "TLS Certificate
              Compression", RFC 8879, DOI 10.17487/RFC8879, December
              2020, <https://www.rfc-editor.org/info/rfc8879>.

   [X.509-IoT]
              Forsby, F., Furuhed, M., Papadimitratos, P., and S. Raza,
              "Lightweight X.509 Digital Certificates for the Internet
              of Things.", Springer, Cham. Lecture Notes of the
              Institute for Computer Sciences, Social Informatics and
              Telecommunications Engineering, vol 242., July 2018,
              <https://doi.org/10.1007/978-3-319-93797-7_14>.

Appendix A.  Example C509 Certificates

A.1.  Example RFC 7925 profiled X.509 Certificate

   Example of [RFC7925] profiled X.509 certificate parsed with OpenSSL.

   Certificate:
       Data:
           Version: 3 (0x2)
           Serial Number: 128269 (0x1f50d)
           Signature Algorithm: ecdsa-with-SHA256
           Issuer: CN=RFC test CA
           Validity
               Not Before: Jan  1 00:00:00 2020 GMT
               Not After : Feb  2 00:00:00 2021 GMT
           Subject: CN=01-23-45-FF-FE-67-89-AB
           Subject Public Key Info:
               Public Key Algorithm: id-ecPublicKey
                   Public-Key: (256 bit)
                   pub:
                       04:b1:21:6a:b9:6e:5b:3b:33:40:f5:bd:f0:2e:69:
                       3f:16:21:3a:04:52:5e:d4:44:50:b1:01:9c:2d:fd:
                       38:38:ab:ac:4e:14:d8:6c:09:83:ed:5e:9e:ef:24:
                       48:c6:86:1c:c4:06:54:71:77:e6:02:60:30:d0:51:
                       f7:79:2a:c2:06
                   ASN1 OID: prime256v1
                   NIST CURVE: P-256
           X509v3 extensions:
               X509v3 Key Usage:
                   Digital Signature
       Signature Algorithm: ecdsa-with-SHA256
            30:44:02:20:44:5d:79:8c:90:e7:f5:00:dc:74:7a:65:4c:ec:
            6c:fa:6f:03:72:76:e1:4e:52:ed:07:fc:16:29:4c:84:66:0d:
            02:20:5a:33:98:5d:fb:d4:bf:dd:6d:4a:cf:38:04:c3:d4:6e:
            bf:3b:7f:a6:26:40:67:4f:c0:35:4f:a0:56:db:ae:a6

   The DER encoding of the above certificate is 314 bytes.

   30 82 01 36 30 81 DE A0 03 02 01 02 02 03 01 F5 0D 30 0A 06 08 2A 86
   48 CE 3D 04 03 02 30 16 31 14 30 12 06 03 55 04 03 0C 0B 52 46 43 20
   74 65 73 74 20 43 41 30 1E 17 0D 32 30 30 31 30 31 30 30 30 30 30 30
   5A 17 0D 32 31 30 32 30 32 30 30 30 30 30 30 5A 30 22 31 20 30 1E 06
   03 55 04 03 0C 17 30 31 2D 32 33 2D 34 35 2D 46 46 2D 46 45 2D 36 37
   2D 38 39 2D 41 42 30 59 30 13 06 07 2A 86 48 CE 3D 02 01 06 08 2A 86
   48 CE 3D 03 01 07 03 42 00 04 B1 21 6A B9 6E 5B 3B 33 40 F5 BD F0 2E
   69 3F 16 21 3A 04 52 5E D4 44 50 B1 01 9C 2D FD 38 38 AB AC 4E 14 D8
   6C 09 83 ED 5E 9E EF 24 48 C6 86 1C C4 06 54 71 77 E6 02 60 30 D0 51
   F7 79 2A C2 06 A3 0F 30 0D 30 0B 06 03 55 1D 0F 04 04 03 02 07 80 30
   0A 06 08 2A 86 48 CE 3D 04 03 02 03 47 00 30 44 02 20 44 5D 79 8C 90
   E7 F5 00 DC 74 7A 65 4C EC 6C FA 6F 03 72 76 E1 4E 52 ED 07 FC 16 29
   4C 84 66 0D 02 20 5A 33 98 5D FB D4 BF DD 6D 4A CF 38 04 C3 D4 6E BF
   3B 7F A6 26 40 67 4F C0 35 4F A0 56 DB AE A6

A.1.1.  Example C509 Certificate Encoding

   The CBOR encoding (~C509Certificate) of the same X.509 certificate is
   shown below in CBOR diagnostic format.

   /This defines a CBOR Sequence (RFC 8742):/

     1,
     h'01f50d',
     "RFC test CA",
     1577836800,
     1612224000,
     h'0123456789AB',
     1,
     h'02B1216AB96E5B3B3340F5BDF02E693F16213A04525ED44450
       B1019C2DFD3838AB',
     1,
     0,
     h'445D798C90E7F500DC747A654CEC6CFA6F037276E14E52ED07
       FC16294C84660D5A33985DFBD4BFDD6D4ACF3804C3D46EBF3B
       7FA62640674FC0354FA056DBAEA6

   The size of the CBOR encoding (CBOR sequence) is 138 bytes.

   01
   43 01 F5 0D
   6B 52 46 43 20 74 65 73 74 20 43 41
   1A 5E 0B E1 00
   1A 60 18 96 00
   46 01 23 45 67 89 AB
   01
   58 21 02 B1 21 6A B9 6E 5B 3B 33 40 F5 BD F0 2E 69 3F 16 21 3A 04 52
   5E D4 44 50 B1 01 9C 2D FD 38 38 AB
   01
   00
   58 40 44 5D 79 8C 90 E7 F5 00 DC 74 7A 65 4C EC 6C FA 6F 03 72 76 E1
   4E 52 ED 07 FC 16 29 4C 84 66 0D 5A 33 98 5D FB D4 BF DD 6D 4A CF 38
   04 C3 D4 6E BF 3B 7F A6 26 40 67 4F C0 35 4F A0 56 DB AE A6

A.1.2.  Example: Natively Signed C509 Certificate

   The corresponding natively signed C509 certificate in CBOR diagnostic
   format is identical, except for cborCertificateType c509CertificateType and
   signatureValue.

   /This defines a CBOR Sequence (RFC 8742):/

     0,
     h'01f50d',
     "RFC test CA",
     1577836800,
     1612224000,
     h'0123456789AB',
     1,
     h'02B1216AB96E5B3B3340F5BDF02E693F16213A04525ED44450
       B1019C2DFD3838AB',
     1,
     6,
     h'B27A0B781455F71B68290F6C2EC9A897F18FDE9B6C59575953
       BC67268AB0E4DDE99D273E04E4715383AB2257C6AAA35284E5
       ED18BDB91247E9F2C433136480B9'

   The size of the CBOR encoding (CBOR sequence) is 138 bytes.

   00
   43 01 F5 0D
   6B 52 46 43 20 74 65 73 74 20 43 41
   1A 5E 0B E1 00
   1A 60 18 96 00
   46 01 23 45 67 89 AB
   01
   58 21 02 B1 21 6A B9 6E 5B 3B 33 40 F5 BD F0 2E 69 3F 16 21 3A 04 52
   5E D4 44 50 B1 01 9C 2D FD 38 38 AB
   01
   00
   58 40 B2 7A 0B 78 14 55 F7 1B 68 29 0F 6C 2E C9 A8 97 F1 8F DE 9B 6C
   59 57 59 53 BC 67 26 8A B0 E4 DD E9 9D 27 3E 04 E4 71 53 83 AB 22 57
   C6 AA A3 52 84 E5 ED 18 BD B9 12 47 E9 F2 C4 33 13 64 80 B9

A.1.3.  Example: Additonal Keys for the Example Certificates

   Below are the issuer key pair and the subject private key belonging
   to the above example certificates.  The private keys are encoded as
   in COSE [RFC8152].  These issuer key pair can be used to sign or
   verify the example certificates and the subject private key allows
   the example certificates to be used in test vectors for other
   protocols like EDHOC.

   issuerPublicKeyAlgorithm :
   1 (EC Public Key (Weierstrass) with secp256r1)

   issuerPublicKey :
   h'02AE4CDB01F614DEFC7121285FDC7F5C6D1D42C95647F061BA0080DF678867845E'

   issuerPrivateKey :
   h'DC66B3415456D649429B53223DF7532B942D6B0E0842C30BCA4C0ACF91547BB2'

   subjectPrivateKey :
   h'D718111F3F9BD91B92FF6877F386BDBFCEA7154268FD7F2FB56EE17D99EA16D4'

A.2.  Example IEEE 802.1AR profiled X.509 Certificate

   EDITOR'S NOTE: To do

A.3.  Example CAB Baseline ECDSA HTTPS X.509 Certificate

   The www.ietf.org HTTPS server replies with a certificate message with
   2 certificates.  The DER encoding of the first certificate is 1209
   bytes.

   30 82 04 b5 30 82 04 5a a0 03 02 01 02 02 10 04 7f a1 e3 19 28 ee 40
   3b a0 b8 3a 39 56 73 fc 30 0a 06 08 2a 86 48 ce 3d 04 03 02 30 4a 31
   0b 30 09 06 03 55 04 06 13 02 55 53 31 19 30 17 06 03 55 04 0a 13 10
   43 6c 6f 75 64 66 6c 61 72 65 2c 20 49 6e 63 2e 31 20 30 1e 06 03 55
   04 03 13 17 43 6c 6f 75 64 66 6c 61 72 65 20 49 6e 63 20 45 43 43 20
   43 41 2d 33 30 1e 17 0d 32 30 30 37 32 39 30 30 30 30 30 30 5a 17 0d
   32 31 30 37 32 39 31 32 30 30 30 30 5a 30 6d 31 0b 30 09 06 03 55 04
   06 13 02 55 53 31 0b 30 09 06 03 55 04 08 13 02 43 41 31 16 30 14 06
   03 55 04 07 13 0d 53 61 6e 20 46 72 61 6e 63 69 73 63 6f 31 19 30 17
   06 03 55 04 0a 13 10 43 6c 6f 75 64 66 6c 61 72 65 2c 20 49 6e 63 2e
   31 1e 30 1c 06 03 55 04 03 13 15 73 6e 69 2e 63 6c 6f 75 64 66 6c 61
   72 65 73 73 6c 2e 63 6f 6d 30 59 30 13 06 07 2a 86 48 ce 3d 02 01 06
   08 2a 86 48 ce 3d 03 01 07 03 42 00 04 96 3e cd d8 4d cd 1b 93 a1 cf
   43 2d 1a 72 17 d6 c6 3b de 33 55 a0 2f 8c fb 5a d8 99 4c d4 4e 20 5f
   15 f6 e3 d2 3b 38 2b a6 49 9b b1 7f 34 1f a5 92 fa 21 86 1f 16 d3 12
   06 63 24 05 fd 70 42 bd a3 82 02 fd 30 82 02 f9 30 1f 06 03 55 1d 23
   04 18 30 16 80 14 a5 ce 37 ea eb b0 75 0e 94 67 88 b4 45 fa d9 24 10
   87 96 1f 30 1d 06 03 55 1d 0e 04 16 04 14 cc 0b 50 e7 d8 37 db f2 43
   f3 85 3d 48 60 f5 3b 39 be 9b 2a 30 2e 06 03 55 1d 11 04 27 30 25 82
   15 73 6e 69 2e 63 6c 6f 75 64 66 6c 61 72 65 73 73 6c 2e 63 6f 6d 82
   0c 77 77 77 2e 69 65 74 66 2e 6f 72 67 30 0e 06 03 55 1d 0f 01 01 ff
   04 04 03 02 07 80 30 1d 06 03 55 1d 25 04 16 30 14 06 08 2b 06 01 05
   05 07 03 01 06 08 2b 06 01 05 05 07 03 02 30 7b 06 03 55 1d 1f 04 74
   30 72 30 37 a0 35 a0 33 86 31 68 74 74 70 3a 2f 2f 63 72 6c 33 2e 64
   69 67 69 63 65 72 74 2e 63 6f 6d 2f 43 6c 6f 75 64 66 6c 61 72 65 49
   6e 63 45 43 43 43 41 2d 33 2e 63 72 6c 30 37 a0 35 a0 33 86 31 68 74
   74 70 3a 2f 2f 63 72 6c 34 2e 64 69 67 69 63 65 72 74 2e 63 6f 6d 2f
   43 6c 6f 75 64 66 6c 61 72 65 49 6e 63 45 43 43 43 41 2d 33 2e 63 72
   6c 30 4c 06 03 55 1d 20 04 45 30 43 30 37 06 09 60 86 48 01 86 fd 6c
   01 01 30 2a 30 28 06 08 2b 06 01 05 05 07 02 01 16 1c 68 74 74 70 73
   3a 2f 2f 77 77 77 2e 64 69 67 69 63 65 72 74 2e 63 6f 6d 2f 43 50 53
   30 08 06 06 67 81 0c 01 02 02 30 76 06 08 2b 06 01 05 05 07 01 01 04
   6a 30 68 30 24 06 08 2b 06 01 05 05 07 30 01 86 18 68 74 74 70 3a 2f
   2f 6f 63 73 70 2e 64 69 67 69 63 65 72 74 2e 63 6f 6d 30 40 06 08 2b
   06 01 05 05 07 30 02 86 34 68 74 74 70 3a 2f 2f 63 61 63 65 72 74 73
   2e 64 69 67 69 63 65 72 74 2e 63 6f 6d 2f 43 6c 6f 75 64 66 6c 61 72
   65 49 6e 63 45 43 43 43 41 2d 33 2e 63 72 74 30 0c 06 03 55 1d 13 01
   01 ff 04 02 30 00 30 82 01 05 06 0a 2b 06 01 04 01 d6 79 02 04 02 04
   81 f6 04 81 f3 00 f1 00 76 00 f6 5c 94 2f d1 77 30 22 14 54 18 08 30
   94 56 8e e3 4d 13 19 33 bf df 0c 2f 20 0b cc 4e f1 64 e3 00 00 01 73
   9c 83 5f 8e 00 00 04 03 00 47 30 45 02 21 00 f8 d1 b4 a9 3d 2f 0d 4c
   41 76 df b4 88 bc c7 3b 86 44 3d 7d e0 0e 6a c8 17 4d 89 48 a8 84 36
   68 02 20 29 ff 5a 34 06 8a 24 0c 69 50 27 88 e8 ee 25 ab 7e d2 cb cf
   68 6e ce 7b 5f 96 b4 31 a9 07 02 fa 00 77 00 5c dc 43 92 fe e6 ab 45
   44 b1 5e 9a d4 56 e6 10 37 fb d5 fa 47 dc a1 73 94 b2 5e e6 f6 c7 0e
   ca 00 00 01 73 9c 83 5f be 00 00 04 03 00 48 30 46 02 21 00 e8 91 c1
   97 bf b0 e3 d3 0c b6 ce e6 0d 94 c3 c7 5f d1 17 53 36 93 11 08 d8 98
   12 d4 d2 9d 81 d0 02 21 00 a1 59 d1 6c 46 47 d1 48 37 57 fc d6 ce 4e
   75 ec 7b 5e f6 57 ef e0 28 f8 e5 cc 47 92 68 2d ac 43 30 0a 06 08 2a
   86 48 ce 3d 04 03 02 03 49 00 30 46 02 21 00 bd 63 cf 4f 7e 5c fe 6c
   29 38 5e a7 1c fb fc 1e 3f 7b 1c d0 72 51 a2 21 f7 77 69 c0 f4 71 df
   ea 02 21 00 b5 c0 6c c4 58 54 fa 30 b2 82 88 b1 d3 bb 9a 66 61 ed 50
   31 72 5b 1a 82 02 e0 da 5b 59 f9 54 02

A.3.1.  Example C509 Certificate Encoding

   The CBOR encoding (~C509Certificate) of the first X.509 certificate
   is shown below in CBOR diagnostic format.

/This defines a CBOR Sequence (RFC 8742):/

1,
h'047FA1E31928EE403BA0B83A395673FC',
[
 -4, "IE", "US",
 -8, "Baltimore",
   -9, "CyberTrust", "Cloudflare, Inc.",
 -1, "Baltimore CyberTrust Root" "Cloudflare Inc ECC CA-3"
],
1595980800,
1627560000,
[
 -4, "US",
 -6, "CA",
 -5, "San Francisco",
 -8, "Cloudflare, Inc.",
 -1, "sni.cloudflaressl.com"
],
1,
h'03963ECDD84DCD1B93A1CF432D1A7217D6C63BDE3355A02F8CFB5AD8994CD44E20',
[
    6,
  7, h'A5CE37EAEBB0750E946788B445FAD9241087961F',
    0,
  1, h'CC0B50E7D837DBF243F3853D4860F53B39BE9B2A',
    2,
  3, [2, "sni.cloudflaressl.com", 2, "www.ietf.org"],
   -1,
 -2, 1,
    7,
  8, [1, 2],
    4,
  5, ["http://crl3.digicert.com/CloudflareIncECCCA-3.crl",
      "http://crl4.digicert.com/CloudflareIncECCCA-3.crl"],
    5,
  6, [h'6086480186FD6C0101', "https://www.digicert.com/CPS",  2],
    8,
  9, [1, "http://ocsp.digicert.com",
      2, "http://cacerts.digicert.com/CloudflareIncECCCA-3.crt"],
   -3,
 -4, -2,
    9, ...
 10, [
       h'F65C942FD1773022145418083094568EE34D131933BFDF0C2F200BCC4EF164E3',
       77922190,
       0,
       h'F8D1B4A93D2F0D4C4176DFB488BCC73B86443D7DE00E6AC8174D8948A8843668
         29FF5A34068A240C69502788E8EE25AB7ED2CBCF686ECE7B5F96B431A90702FA',
       h'5CDC4392FEE6AB4544B15E9AD456E61037FBD5FA47DCA17394B25EE6F6C70ECA',
       77922238,
       0,
       h'E891C197BFB0E3D30CB6CEE60D94C3C75FD1175336931108D89812D4D29D81D0
         A159D16C4647D1483757FCD6CE4E75EC7B5EF657EFE028F8E5CC4792682DAC43'
     ]
],
0,
h'BD63CF4F7E5CFE6C29385EA71CFBFC1E3F7B1CD07251A221F77769C0F471DFEA
  B5C06CC45854FA30B28288B1D3BB9A6661ED5031725B1A8202E0DA5B59F95402'
   The size of the CBOR encoding (CBOR sequence) is 781 bytes.

A.4.  Example CAB Baseline RSA HTTPS X.509 Certificate

   The tools.ietf.org HTTPS server replies with a certificate message
   with 4 certificates.  The DER encoding of the first certificate is
   1647 bytes.

   30 82 06 6b 30 82 05 53 a0 03 02 01 02 02 09 00 a6 a5 5c 87 0e 39 b4
   0e 30 0d 06 09 2a 86 48 86 f7 0d 01 01 0b 05 00 30 81 c6 31 0b 30 09
   06 03 55 04 06 13 02 55 53 31 10 30 0e 06 03 55 04 08 13 07 41 72 69
   7a 6f 6e 61 31 13 30 11 06 03 55 04 07 13 0a 53 63 6f 74 74 73 64 61
   6c 65 31 25 30 23 06 03 55 04 0a 13 1c 53 74 61 72 66 69 65 6c 64 20
   54 65 63 68 6e 6f 6c 6f 67 69 65 73 2c 20 49 6e 63 2e 31 33 30 31 06
   03 55 04 0b 13 2a 68 74 74 70 3a 2f 2f 63 65 72 74 73 2e 73 74 61 72
   66 69 65 6c 64 74 65 63 68 2e 63 6f 6d 2f 72 65 70 6f 73 69 74 6f 72
   79 2f 31 34 30 32 06 03 55 04 03 13 2b 53 74 61 72 66 69 65 6c 64 20
   53 65 63 75 72 65 20 43 65 72 74 69 66 69 63 61 74 65 20 41 75 74 68
   6f 72 69 74 79 20 2d 20 47 32 30 1e 17 0d 32 30 31 30 30 31 31 39 33
   38 33 36 5a 17 0d 32 31 31 31 30 32 31 39 33 38 33 36 5a 30 3e 31 21
   30 1f 06 03 55 04 0b 13 18 44 6f 6d 61 69 6e 20 43 6f 6e 74 72 6f 6c
   20 56 61 6c 69 64 61 74 65 64 31 19 30 17 06 03 55 04 03 0c 10 2a 2e
   74 6f 6f 6c 73 2e 69 65 74 66 2e 6f 72 67 30 82 01 22 30 0d 06 09 2a
   86 48 86 f7 0d 01 01 01 05 00 03 82 01 0f 00 30 82 01 0a 02 82 01 01
   00 b1 e1 37 e8 eb 82 d6 89 fa db f5 c2 4b 77 f0 2c 4a de 72 6e 3e 13
   60 d1 a8 66 1e c4 ad 3d 32 60 e5 f0 99 b5 f4 7a 7a 48 55 21 ee 0e 39
   12 f9 ce 0d ca f5 69 61 c7 04 ed 6e 0f 1d 3b 1e 50 88 79 3a 0e 31 41
   16 f1 b1 02 64 68 a5 cd f5 4a 0a ca 99 96 35 08 c3 7e 27 5d d0 a9 cf
   f3 e7 28 af 37 d8 b6 7b dd f3 7e ae 6e 97 7f f7 ca 69 4e cc d0 06 df
   5d 27 9b 3b 12 e7 e6 fe 08 6b 52 7b 82 11 7c 72 b3 46 eb c1 e8 78 b8
   0f cb e1 eb bd 06 44 58 dc 83 50 b2 a0 62 5b dc 81 b8 36 e3 9e 7c 79
   b2 a9 53 8a e0 0b c9 4a 2a 13 39 31 13 bd 2c cf a8 70 cf 8c 8d 3d 01
   a3 88 ae 12 00 36 1d 1e 24 2b dd 79 d8 53 01 26 ed 28 4f c9 86 94 83
   4e c8 e1 14 2e 85 b3 af d4 6e dd 69 46 af 41 25 0e 7a ad 8b f2 92 ca
   79 d9 7b 32 4f f7 77 e8 f9 b4 4f 23 5c d4 5c 03 ae d8 ab 3a ca 13 5f
   5d 5d 5d a1 02 03 01 00 01 a3 82 02 e1 30 82 02 dd 30 0c 06 03 55 1d
   13 01 01 ff 04 02 30 00 30 1d 06 03 55 1d 25 04 16 30 14 06 08 2b 06
   01 05 05 07 03 01 06 08 2b 06 01 05 05 07 03 02 30 0e 06 03 55 1d 0f
   01 01 ff 04 04 03 02 05 a0 30 3d 06 03 55 1d 1f 04 36 30 34 30 32 a0
   30 a0 2e 86 2c 68 74 74 70 3a 2f 2f 63 72 6c 2e 73 74 61 72 66 69 65
   6c 64 74 65 63 68 2e 63 6f 6d 2f 73 66 69 67 32 73 31 2d 32 34 32 2e
   63 72 6c 30 63 06 03 55 1d 20 04 5c 30 5a 30 4e 06 0b 60 86 48 01 86
   fd 6e 01 07 17 01 30 3f 30 3d 06 08 2b 06 01 05 05 07 02 01 16 31 68
   74 74 70 3a 2f 2f 63 65 72 74 69 66 69 63 61 74 65 73 2e 73 74 61 72
   66 69 65 6c 64 74 65 63 68 2e 63 6f 6d 2f 72 65 70 6f 73 69 74 6f 72
   79 2f 30 08 06 06 67 81 0c 01 02 01 30 81 82 06 08 2b 06 01 05 05 07
   01 01 04 76 30 74 30 2a 06 08 2b 06 01 05 05 07 30 01 86 1e 68 74 74
   70 3a 2f 2f 6f 63 73 70 2e 73 74 61 72 66 69 65 6c 64 74 65 63 68 2e
   63 6f 6d 2f 30 46 06 08 2b 06 01 05 05 07 30 02 86 3a 68 74 74 70 3a
   2f 2f 63 65 72 74 69 66 69 63 61 74 65 73 2e 73 74 61 72 66 69 65 6c
   64 74 65 63 68 2e 63 6f 6d 2f 72 65 70 6f 73 69 74 6f 72 79 2f 73 66
   69 67 32 2e 63 72 74 30 1f 06 03 55 1d 23 04 18 30 16 80 14 25 45 81
   68 50 26 38 3d 3b 2d 2c be cd 6a d9 b6 3d b3 66 63 30 2b 06 03 55 1d
   11 04 24 30 22 82 10 2a 2e 74 6f 6f 6c 73 2e 69 65 74 66 2e 6f 72 67
   82 0e 74 6f 6f 6c 73 2e 69 65 74 66 2e 6f 72 67 30 1d 06 03 55 1d 0e
   04 16 04 14 ad 8a b4 1c 07 51 d7 92 89 07 b0 b7 84 62 2f 36 55 7a 5f
   4d 30 82 01 06 06 0a 2b 06 01 04 01 d6 79 02 04 02 04 81 f7 04 81 f4
   00 f2 00 77 00 f6 5c 94 2f d1 77 30 22 14 54 18 08 30 94 56 8e e3 4d
   13 19 33 bf df 0c 2f 20 0b cc 4e f1 64 e3 00 00 01 74 e5 ac 71 13 00
   00 04 03 00 48 30 46 02 21 00 8c f5 48 52 ce 56 35 43 39 11 cf 10 cd
   b9 1f 52 b3 36 39 22 3a d1 38 a4 1d ec a6 fe de 1f e9 0f 02 21 00 bc
   a2 25 43 66 c1 9a 26 91 c4 7a 00 b5 b6 53 ab bd 44 c2 f8 ba ae f4 d2
   da f2 52 7c e6 45 49 95 00 77 00 5c dc 43 92 fe e6 ab 45 44 b1 5e 9a
   d4 56 e6 10 37 fb d5 fa 47 dc a1 73 94 b2 5e e6 f6 c7 0e ca 00 00 01
   74 e5 ac 72 3c 00 00 04 03 00 48 30 46 02 21 00 a5 e0 90 6e 63 e9 1d
   4f dd ef ff 03 52 b9 1e 50 89 60 07 56 4b 44 8a 38 28 f5 96 dc 6b 28
   72 6d 02 21 00 fc 91 ea ed 02 16 88 66 05 4e e1 8a 2e 53 46 c4 cc 51
   fe b3 fa 10 a9 1d 2e db f9 91 25 f8 6c e6 30 0d 06 09 2a 86 48 86 f7
   0d 01 01 0b 05 00 03 82 01 01 00 14 04 3f a0 be d2 ee 3f a8 6e 3a 1f
   78 8e a0 4c 35 53 0f 11 06 1f ff 60 a1 6d 0b 83 e9 d9 2a db b3 3f 9d
   b3 d7 e0 59 4c 19 a8 e4 19 a5 0c a7 70 72 77 63 d5 fe 64 51 0a d2 7a
   d6 50 a5 8a 92 38 ec cb 2f 0f 5a c0 64 58 4d 5c 06 b9 73 63 68 27 8b
   89 34 dc 79 c7 1d 3a fd 34 5f 83 14 41 58 49 80 68 29 80 39 8a 86 72
   69 cc 79 37 ce e3 97 f7 dc f3 95 88 ed 81 03 29 00 d2 a2 c7 ba ab d6
   3a 8e ca 09 0b d9 fb 39 26 4b ff 03 d8 8e 2d 3f 6b 21 ca 8a 7d d8 5f
   fb 94 ba 83 de 9c fc 15 8d 61 fa 67 2d b0 c7 db 3d 25 0a 41 4a 85 d3
   7f 49 46 37 3c f4 b1 75 d0 52 f3 dd c7 66 f1 4b fd aa 00 ed bf e4 7e
   ed 01 ec 7b e4 f6 46 fc 31 fd 72 fe 03 d2 f2 65 af 4d 7e e2 81 9b 7a
   fd 30 3c f5 52 f4 05 34 a0 8a 3e 19 41 58 c8 a8 e0 51 71 84 09 15 ae
   ec a5 77 75 fa 18 f7 d5 77 d5 31 cc c7 2d

A.4.1.  Example C509 Certificate Encoding

   The CBOR encoding (~C509Certificate) of the first X.509 certificate
   is shown below in CBOR diagnostic format.

/This defines a CBOR Sequence (RFC 8742):/

1,
h'A6A55C870E39B40E',
[
 -4, "US",
 -6, "Arizona",
 -5, "Scottsdale",
 -8, "Starfield Technologies, Inc.",
 -9, "http://certs.starfieldtech.com/repository/",
 -1, "Starfield Secure Certificate Authority - G2"
],
1601581116,
1635881916,
[
  -9, "Domain Control Validated",
   1, "*.tools.ietf.org"
],
0,
h'B1E137E8EB82D689FADBF5C24B77F02C4ADE726E3E1360D1A8661EC4AD3D3260
  E5F099B5F47A7A485521EE0E3912F9CE0DCAF56961C704ED6E0F1D3B1E508879
  3A0E314116F1B1026468A5CDF54A0ACA99963508C37E275DD0A9CFF3E728AF37
  D8B67BDDF37EAE6E977FF7CA694ECCD006DF5D279B3B12E7E6FE086B527B8211
  7C72B346EBC1E878B80FCBE1EBBD064458DC8350B2A0625BDC81B836E39E7C79
  B2A9538AE00BC94A2A13393113BD2CCFA870CF8C8D3D01A388AE1200361D1E24
  2BDD79D8530126ED284FC98694834EC8E1142E85B3AFD46EDD6946AF41250E7A
  AD8BF292CA79D97B324FF777E8F9B44F235CD45C03AED8AB3ACA135F5D5D5DA1',
[
 -3,
 -4, -2,
  7,
  8, [ 1, 2 ],
 -1,
 -2, 5,
  4, "http://crl.starfieldtech.com/sfig2s1-242.crl",
  5, "http://crl.starfieldtech.com/sfig2s1-242.crl",
  6, [ h'6086480186fd6e01071701',
       "http://certificates.starfieldtech.com/repository/", 1 ],
  8,
  9, [ 1, "http://ocsp.starfieldtech.com/",
       2, "http://certificates.starfieldtech.com/repository/sfig2.crt" ],
  6,
  7, h'254581685026383D3B2D2CBECD6AD9B63DB36663',
  2,
  3, [ 2, "*.tools.ietf.org", 2, "tools.ietf.org" ],
  0,
  1, h'AD8AB41C0751D7928907B0B784622F36557A5F4D',
  9,
 10, [
       h'F65C942FD1773022145418083094568EE34D131933BFDF0C2F200BCC4EF164E3',
       1715,
       1,
       0,
       h'8CF54852CE5635433911CF10CDB91F52B33639223AD138A41DECA6FEDE1FE90F
         BCA2254366C19A2691C47A00B5B653ABBD44C2F8BAAEF4D2DAF2527CE6454995',
       h'5CDC4392FEE6AB4544B15E9AD456E61037FBD5FA47DCA17394B25EE6F6C70ECA',
       2012,
       1,
       0,
       h'A5E0906E63E91D4FDDEFFF0352B91E50896007564B448A3828F596DC6B28726D
         FC91EAED02168866054EE18A2E5346C4CC51FEB3FA10A91D2EDBF99125F86CE6'
     ]
],
23,
h'14043FA0BED2EE3FA86E3A1F788EA04C35530F11061FFF60A16D0B83E9D92ADB
  B33F9DB3D7E0594C19A8E419A50CA770727763D5FE64510AD27AD650A58A9238
  ECCB2F0F5AC064584D5C06B9736368278B8934DC79C71D3AFD345F8314415849
  80682980398A867269CC7937CEE397F7DCF39588ED81032900D2A2C7BAABD63A
  8ECA090BD9FB39264BFF03D88E2D3F6B21CA8A7DD85FFB94BA83DE9CFC158D61
  FA672DB0C7DB3D250A414A85D37F4946373CF4B175D052F3DDC766F14BFDAA00
  EDBFE47EED01EC7BE4F646FC31FD72FE03D2F265AF4D7EE2819B7AFD303CF552
  F40534A08A3E194158C8A8E05171840915AEECA57775FA18F7D577D531CCC72D'

   The size of the CBOR encoding (CBOR sequence) is 1242 bytes.

Acknowledgments

   The authors want to thank Henk Birkholz, Carsten Bormann, Russ
   Housley, Olle Johansson, Benjamin Kaduk, Ilari Liusvaara, Laurence
   Lundblade, Thomas Peterson, Michael Richardson, Stefan Santesson, Jim
   Schaad, Fraser Tweedale, and Rene Struik for reviewing and commenting
   on intermediate versions of the draft.

Authors' Addresses

   Shahid Raza
   RISE AB

   Email: shahid.raza@ri.se

   Joel Hoeglund
   RISE AB

   Email: joel.hoglund@ri.se

   Goeran Selander
   Ericsson AB

   Email: goran.selander@ericsson.com

   John Preuss Mattsson
   Ericsson AB

   Email: john.mattsson@ericsson.com

   Martin Furuhed
   Nexus Group

   Email: martin.furuhed@nexusgroup.com