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SPKI Examples                                            Carl M. Ellison
INTERNET-DRAFT                                           CyberCash, Inc.
Expires: 15 September 1998
                                                             Bill Frantz
                                                    Electric Communities

                                                          Butler Lampson

                                                              Ron Rivest
                                     MIT Laboratory for Computer Science

                                                         Brian M. Thomas
                                                       Southwestern Bell

                                                             Tatu Ylonen

                                                           10 March 1998

                             SPKI Examples
                             ---- --------


Status of This Document

   This document supersedes the draft filed under the name draft-ietf-
   spki-cert-examples-00.txt.  This draft contains examples of SPKI
   structures for various applications.  The structure definition is to
   be found in draft-ietf-spki-cert-structure-*.txt and the theory
   behind SPKI certificates is to be found in draft-ietf-spki-cert-

   Distribution of this document is unlimited.  Comments should be sent
   to the SPKI (Simple Public Key Infrastructure) Working Group mailing
   list <spki@c2.net> or to the authors.

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months.  Internet-Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a

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   ``working draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on ds.internic.net (East USA), ftp.isi.edu (West USA),
   nic.nordu.net (North Europe), ftp.nis.garr.it (South Europe),
   munnari.oz.au (Pacific Rim), or ftp.is.co.za (Africa).


   SPKI structures are defined for public keys, hash values, access
   control list (ACL) entries and certificates.  This document gives
   examples of such structures for real world applications.  The
   examples here are not tied to any specific application and should be
   taken as informative examples rather than standard formats.  However,
   once applications are fielded using such structures and we have
   experience with them, we can consider publishing those formats as
   proposed standards.  That effort is considered out of scope for this

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Table of Contents

      Status of This Document....................................1

      Table of Contents..........................................3

      1. SPKI Basic Structures...................................4

      2. Tag Examples............................................6
      2.1 FTP....................................................6
      2.2 HTTP...................................................6
      2.3 TELNET.................................................6
      2.4 Public Key Protected File System tags..................6
      2.5 Authority to spend money...............................8
      2.6 Purchase order signing permission......................8

      3. Keyholder examples......................................9
      3.1 Locator certificate....................................9
      3.2 Insurance certificate.................................10
      3.3 Auto-certificate......................................10

      4. Object certificates....................................11
      4.1 PICS-like ratings certificate.........................11
      4.2 Virus checking certificate............................11

      5. Full sequence, with auto-certificate...................12

      Authors' Addresses........................................14
      Expiration and File Name..................................15

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1. SPKI Basic Structures

   An SPKI certificate has five fields of interest during trust
   1.  Issuer -- the principal issuing this certificate and granting the
       permission or rights it communicates
   2.  Subject -- the principal or name acquiring the permission or
   3.  Delegation -- a flag noting whether the Subject is also acquiring
       the right to delegate all or part of the permission it acquires
       through this certificate
   4.  Authorization <tag> -- a field specifying the permission being
   5.  Validity -- a specification of the dates or on-line conditions
       under which the certificate is assumed to be valid

   An SPKI ACL entry generates the same five fields, for trust
   computation, but does not need to contain them all.  The Issuer is
   always "self" and is omitted from the structure.  If the ACL is held
   in editable memory, then the Validity fields can be omitted on the
   assumption that if the owner of the ACL wants to declare an entry
   invalid, he can edit it immediately.  However, for ACLs built into
   executable software, running remotely, this assumption may not hold
   true and one might want validity fields.

   The purpose of SPKI structures is to communicate permission or rights
   from one keyholder to another.  If we consider this flow to go
   horizontally from left to right, at the left end of the flow one
   finds the injection of permission.  This is always in the form of an
   access control list (ACL) entry.  An ACL entry is like a certificate,
   except that it has no issuer and is not signed.  It is protected in
   the application by other means.

   To the right of the ACL entry, one finds certificates.  At least for
   the sake of discussion, there are two forms of certificate: one that
   communicates permissions and one that defines names.  It is possible
   to unify the two, but for our purposes, they will be considered

   A basic SPKI certificate communicates a permission from one key to
   another key (equivalently from one principal to another principal or
   from one keyholder to another keyholder).  In the process, it can
   pass all permissions it has been handed, in which case it uses (tag
   (*)) as its tag field or it can pass only certain permissions.  The
   former can be considered a group membership certificate.  That is,
   the subject key is a full member of the group defined by the issuer
   key.  Any permissions given the issuer are inherited by the subject.
   If the subject is a name rather than a key, then the permission is
   being granted to the named key.  That is, it is assumed that the name
   will be reduced to a key before permissions propagate.  This is

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   especially important when considering the propagation of the
   permission to delegate.  A named key may be given a permission
   without the permission to delegate, but that name could define a
   group and could therefore represent implicit delegation.

   A name certificate maps a name (in the issuer field) to either a key
   or a name (in the subject field).  It is always a group membership
   style of certificate -- that is with (tag (*)).

   The bulk of what changes with each example in the next section is the
   <tag> field, so we assume the following certificate template:

     (issuer (hash sha1 |TLCgPLFlGTzgUbcaYLW8kGTEnUk=|))
     (subject (hash sha1 |Ve1L/7MqiJcj+LSa/l10fl3tuTQ=|))
     (not-before "1998-03-01_12:42:17")
     (not-after "2012-01-01_00:00:00")

   or ACL template:

       (subject (hash sha1 |Ve1L/7MqiJcj+LSa/l10fl3tuTQ=|))

   with a tag and possibly delegation field where the "..." is in the
   middle of the structures above.

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2. Tag Examples

   The <tag> fields listed here are not meant to be an exhaustive list
   of all possible <tag>s.  Such is not possible.  The final arbiter of
   what needs to be an <tag> and what parameters a particular <tag>
   needs is the designer of the code that verifies a certificate, e.g.,
   to grant access.  Listed here are <tag> fields we suspect might be
   useful and we present these here as a guide to the developer's

2.1 FTP

   (tag (ftp cybercash.com cme))

   This <tag> indicates that the Subject has permission to do FTP into
   host cybercash.com as user cme.

2.2 HTTP

   (tag (http http://acme.com/company-private/personnel ))

   This <tag> gives the Subject permission to access the web page at the
   given URI.  To give permission for an entire tree under a given URI,
   one might use:

   (tag (http (* prefix http://acme.com/company-private/personnel/ )))


   (tag (telnet clark.net cme ))

   This <tag> gives the Subject permission to telnet into host clark.net
   as user cme.

2.4 Public Key Protected File System tags

   (tag (pkpfs <pathname> <access> ))

   refers to a hypothetical distributed file system whose access is
   controlled by public key challenge/response.  The <pathname> can be a
   single pathname, a set of files (specified by normal "*" convention)
   or a directory sub-structure (specified by (* prefix ...)).  For

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   (tag (pkpfs //ftp.clark.net/pub/cme/spki.txt (* set read write)))

   would give read and write access to that one file on that one host
   machine, while

   (tag (pkpfs //ftp.clark.net/pub/cme/spki.* (* set read write)))

   would give read and write access to all files starting with "spki.".

   (tag (pkpfs //ftp.clark.net/pub/cme/ add))

   would give permission to add new files to that directory and

   (tag (pkpfs (* prefix //ftp.clark.net/pub/cme/) read ))

   would give read permission to all files in that directory.

   The full specification of possible <access> specifications is up to
   the implementer of this file system.

   One might also want to grant disk quotas for this file system, e.g.,

   (tag (pkpfs-quota (* range le "50000" )))

   One could have used

   (tag (pkpfs-quota "50000" ))

   to express the quota, but the (* range ...) form permits the user to
   delegate a sub-quota to some other user.

   Accounting for such quotas could be interesting, but one would
   probably want to charge each K of disk to all users in the
   certificate delegation chain, since the disk accounting system is not
   aware of acts of delegation and therefore can not reduce the quota of
   the delegator.  To maintain good accounting, this would require each
   file to have a list of accounts (key hashes) against which its size
   is charged -- so that when a file is deleted, the appropriate quotas
   can be adjusted.  Since there would probably be only a small number
   of different such chains of delegation, one might keep such lists
   separately from file nodes.  However, these are details left to the
   designer of the PKPFS.

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2.5 Authority to spend money

   (tag (spend <bank> <account> (* range le <amount> )))

   indicates that the subject has authority to authorize spending up to
   <amount> per electronic check from <account> at <bank>.  For example,

   (tag (spend BankBoston "011000390 436 20608" (* range le "500.00")))

   permits someone to spend up to 500.00 per electronic check from the
   indicated checking account at BankBoston.  [The account number above
   was chosen randomly and is hopefully not a valid BankBoston account.]

   (propagate) implies that this account holder has the permission to
   delegate check-writing ability to others (e.g., family members or
   temporary public keys (for use on a laptop while traveling)).

2.6 Purchase order signing permission

   (tag (purchase (* range le <amount>) (* set <<items>> )))

   might indicate permission to issue a purchase order.  The amount of
   the purchase order is limited by the second element of the (purchase
   ) S-expression and, optionally, a list of purchasable items is given
   as the third element.  The company whose purchase orders are
   permitted to be signed here will appear in the certificate permission
   chain leading to the final purchase order.  Specifically, that
   company's key will be the issuer at the head of the (purchase )

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3. Keyholder examples

   The set of examples in this section deals with (keyholder) subjects.
   These are for human consumption, since the subject is a human being
   (the keyholder of a particular key) rather than a key in cyberspace.
   Note that it is not meaningful for a keyholder certificate to have
   the (propagate) flag.

3.1 Locator certificate

   A locator certificate is one that is issued by a company that
   promises to keep track of the indicated keyholder until the not-after
   date, and promises to serve the keyholder with papers for the
   indicated fee in the indicated currency, up until the not-after date.

   This kind of certificate might be used to back up a legal contract in
   which the keyholder might have to pay damages at some future date, in
   the event of non-performance, so that it becomes important to know
   how to sue that keyholder at that later date.  An old fashioned
   "identity certificate" doesn't serve as well here because it lists
   some information about the keyholder that might be used to track that
   person down, but that information is old by the time the contract is
   signed and it is the ability to locate that keyholder at the end of
   the contract that is important.  Maintaining that ability costs money
   and therefore the issuer of the locator certificate expects to be
   paid for its services.  The issuer might also charge the keyholder at
   the time of certificate issuance, but that fee need not be indicated
   in the certificate.

   For example:

    (issuer (hash md5 |u2kl73MiObh5o1zkGmHdbA==|))
    (subject (keyholder (hash md5 |kuXyqx8jYWdZ/j7Vffr+yg==| )))
    (tag (tracking-fee "150" USD))
    (not-after "2003-01-01_00:00:00")


   notes in its tag field that the issuer will serve papers on the
   indicated keyholder for a tracking fee of $150 until the beginning of

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3.2 Insurance certificate

   Instead of tracking down a keyholder and serving papers on him or
   her, the person relying on a certificate might prefer that some
   insurance company pay the penalty amount in the event of non-
   performance, and then worry on its own about collecting that fee
   (plus damages, no doubt) from the keyholder.  This kind of
   certificate, like an insurance policy, will cost the user of the
   certificate money at the time it is issued.  It is therefore good for
   only one user.

   For example:

    (issuer (hash md5 |u2kl73MiObh5o1zkGmHdbA==|))
    (subject (keyholder (hash md5 |kuXyqx8jYWdZ/j7Vffr+yg==| )))
    (tag (insured "50000" USD) (to (hash md5 |1r8ICXryJw6v/B4MQdTU/Q==|))
     (for "Failure to perform under contract (on file): "
       (hash md5 |gPA50iM6yETsixLgo2kVlA==|)))
    (not-after "2003-01-01_00:00:00")

   represents a promise to pay $50000 to |1r8ICXryJw6v/B4MQdTU/Q==| in
   the event that the keyholder of |kuXyqx8jYWdZ/j7Vffr+yg==| fails to
   fulfill the contract, |gPA50iM6yETsixLgo2kVlA==|.

3.3 Auto-certificate

   There are some pieces of information about which the proper issuer is
   the subject.  The name a keyholder prefers to be called, the phone
   number or e-mail address at which the keyholder can be reached, etc.,
   are all items of information about which the keyholder is the best

    (issuer (hash sha1 |1QvsTPF0/vqHPGODX/yEN8ro+sc=|))
    (subject (keyholder (hash sha1 |1QvsTPF0/vqHPGODX/yEN8ro+sc=|)))
     (* set
      (name "Carl")
      (e-mail "cme@acm.org") ) ) )


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4. Object certificates

   The certificates in this section have subjects that are objects
   rather than keys or keyholders.  As with keyholder certificates, it
   is not meaningful for object certificates to have the (propagate)

4.1 PICS-like ratings certificate

    (issuer (hash md5 |Ut9m14byPzdbCNZWdDjNQg==|))
      (hash md5 |vN6ySKWE9K6T6cP9U5wntA==|
    (tag (ratings (sex "1") (violence "0") (crypto "9")))


   This certificate should be self-explanatory.  This assigns attributes
   to the indicated object (a web page with the indicated hash).

4.2 Virus checking certificate

    (issuer (hash md5 |Ut9m14byPzdbCNZWdDjNQg==|))
      (hash md5 |szKSlSK+SNzIsHH3wjAsTQ==| runemacs.exe)))
    (tag virus-free)


   This certificate is even simpler.  The issuer is declaring that the
   indicated object has been checked and is virus free, in the issuer's

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5. Full sequence, with auto-certificate

   For one full example of a real certificate, the following sequence
   presents the public key used, calls for the verifier to hash it (and
   store it away, to be referred to later by its hash), gives a
   certificate body and then a signature (which by side-effect calls for
   the previous object to be stored and hashed by the signature
   algorithm's hash function).  The example used is a temporary auto-

      (e #11#)
    (do hash md5)
     (issuer (hash md5 |+gbUgUltGysNgewRwu/3hQ==|))
      (keyholder (hash md5 |+gbUgUltGysNgewRwu/3hQ==|)))
      (* set
       (name "Carl M. Ellison")
       (street "207 Grindall St.")
       (city "Baltimore MD")
       (zip "21230-4103")))
     (not-after "1998-04-15_00:00:00"))
     (hash md5 |54LeOBILOUpskE5xRTSmmA==|)
     (hash md5 |+gbUgUltGysNgewRwu/3hQ==|)

   or, in base64:


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Authors' Addresses

   Carl M. Ellison
   CyberCash, Inc.
   207 Grindall Street
   Baltimore MD 21230-4103 USA

   Telephone:      +1 410-727-4288
                   +1 410-727-4293(FAX)
                   +1 703-620-4200(main office, Reston, Virginia, USA)
   EMail:          cme@cybercash.com
   Web:            http://www.clark.net/pub/cme

   Bill Frantz
   Electric Communities
   10101 De Anza Blvd.
   Cupertino CA 95014

   Telephone:      +1 408-342-9576
   Email:          frantz@netcom.com

   Butler Lampson
   180 Lake View Ave
   Cambridge MA 02138

   Telephone:      +1 617-547-9580 (voice + FAX)
   EMail:          blampson@microsoft.com

   Ron Rivest
   Room 324, MIT Laboratory for Computer Science
   545 Technology Square
   Cambridge MA 02139

   Telephone:      +1-617-253-5880
   Email:          rivest@theory.lcs.mit.edu
   Web:            http://theory.lcs.mit.edu/~rivest

   Brian Thomas
   Southwestern Bell
   One Bell Center, Room 23Q1
   St. Louis MO 63101 USA

   Telephone:      +1 314-235-3141

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                   +1 314-331-2755(FAX)
   EMail:          bt0008@entropy.sbc.com

   Tatu Ylonen
   SSH Communications Security Ltd.
   Tekniikantie 12
   FIN-02150 ESPOO

   E-mail:         ylo@ssh.fi

Expiration and File Name

   This draft expires 15 September 1998.

   Its file name is draft-ietf-spki-cert-examples-01.txt

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