draft-ietf-acme-acme-12.txt   draft-ietf-acme-acme-13.txt 
ACME Working Group R. Barnes ACME Working Group R. Barnes
Internet-Draft Cisco Internet-Draft Cisco
Intended status: Standards Track J. Hoffman-Andrews Intended status: Standards Track J. Hoffman-Andrews
Expires: October 26, 2018 EFF Expires: January 18, 2019 EFF
D. McCarney D. McCarney
Let's Encrypt Let's Encrypt
J. Kasten J. Kasten
University of Michigan University of Michigan
April 24, 2018 July 17, 2018
Automatic Certificate Management Environment (ACME) Automatic Certificate Management Environment (ACME)
draft-ietf-acme-acme-12 draft-ietf-acme-acme-13
Abstract Abstract
Certificates in PKI using X.509 (PKIX) are used for a number of Certificates in PKI using X.509 (PKIX) are used for a number of
purposes, the most significant of which is the authentication of purposes, the most significant of which is the authentication of
domain names. Thus, certificate authorities in the Web PKI are domain names. Thus, certificate authorities in the Web PKI are
trusted to verify that an applicant for a certificate legitimately trusted to verify that an applicant for a certificate legitimately
represents the domain name(s) in the certificate. Today, this represents the domain name(s) in the certificate. Today, this
verification is done through a collection of ad hoc mechanisms. This verification is done through a collection of ad hoc mechanisms. This
document describes a protocol that a certification authority (CA) and document describes a protocol that a certification authority (CA) and
skipping to change at page 2, line 7 skipping to change at page 2, line 7
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 26, 2018. This Internet-Draft will expire on January 18, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Deployment Model and Operator Experience . . . . . . . . . . 5 2. Deployment Model and Operator Experience . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7 4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
5. Character Encoding . . . . . . . . . . . . . . . . . . . . . 9 5. Character Encoding . . . . . . . . . . . . . . . . . . . . . 10
6. Message Transport . . . . . . . . . . . . . . . . . . . . . . 9 6. Message Transport . . . . . . . . . . . . . . . . . . . . . . 10
6.1. HTTPS Requests . . . . . . . . . . . . . . . . . . . . . 9 6.1. HTTPS Requests . . . . . . . . . . . . . . . . . . . . . 10
6.2. Request Authentication . . . . . . . . . . . . . . . . . 10 6.2. Request Authentication . . . . . . . . . . . . . . . . . 11
6.3. Request URL Integrity . . . . . . . . . . . . . . . . . . 12 6.3. Request URL Integrity . . . . . . . . . . . . . . . . . . 12
6.3.1. "url" (URL) JWS Header Parameter . . . . . . . . . . 12 6.3.1. "url" (URL) JWS Header Parameter . . . . . . . . . . 13
6.4. Replay protection . . . . . . . . . . . . . . . . . . . . 12 6.4. Replay protection . . . . . . . . . . . . . . . . . . . . 13
6.4.1. Replay-Nonce . . . . . . . . . . . . . . . . . . . . 13 6.4.1. Replay-Nonce . . . . . . . . . . . . . . . . . . . . 14
6.4.2. "nonce" (Nonce) JWS Header Parameter . . . . . . . . 14 6.4.2. "nonce" (Nonce) JWS Header Parameter . . . . . . . . 14
6.5. Rate Limits . . . . . . . . . . . . . . . . . . . . . . . 14 6.5. Rate Limits . . . . . . . . . . . . . . . . . . . . . . . 14
6.6. Errors . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.6. Errors . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.6.1. Subproblems . . . . . . . . . . . . . . . . . . . . . 16 6.6.1. Subproblems . . . . . . . . . . . . . . . . . . . . . 17
7. Certificate Management . . . . . . . . . . . . . . . . . . . 17 7. Certificate Management . . . . . . . . . . . . . . . . . . . 18
7.1. Resources . . . . . . . . . . . . . . . . . . . . . . . . 17 7.1. Resources . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.1. Directory . . . . . . . . . . . . . . . . . . . . . . 20 7.1.1. Directory . . . . . . . . . . . . . . . . . . . . . . 20
7.1.2. Account Objects . . . . . . . . . . . . . . . . . . . 22 7.1.2. Account Objects . . . . . . . . . . . . . . . . . . . 22
7.1.3. Order Objects . . . . . . . . . . . . . . . . . . . . 23 7.1.3. Order Objects . . . . . . . . . . . . . . . . . . . . 23
7.1.4. Authorization Objects . . . . . . . . . . . . . . . . 26 7.1.4. Authorization Objects . . . . . . . . . . . . . . . . 26
7.1.5. Challenge Objects . . . . . . . . . . . . . . . . . . 27 7.1.5. Challenge Objects . . . . . . . . . . . . . . . . . . 28
7.1.6. Status Changes . . . . . . . . . . . . . . . . . . . 27 7.1.6. Status Changes . . . . . . . . . . . . . . . . . . . 28
7.2. Getting a Nonce . . . . . . . . . . . . . . . . . . . . . 30 7.2. Getting a Nonce . . . . . . . . . . . . . . . . . . . . . 30
7.3. Account Creation . . . . . . . . . . . . . . . . . . . . 31 7.3. Account Creation . . . . . . . . . . . . . . . . . . . . 31
7.3.1. Finding an Account URL Given a Key . . . . . . . . . 33 7.3.1. Finding an Account URL Given a Key . . . . . . . . . 33
7.3.2. Account Update . . . . . . . . . . . . . . . . . . . 33 7.3.2. Account Update . . . . . . . . . . . . . . . . . . . 34
7.3.3. Account Information . . . . . . . . . . . . . . . . . 34 7.3.3. Account Information . . . . . . . . . . . . . . . . . 34
7.3.4. Changes of Terms of Service . . . . . . . . . . . . . 34 7.3.4. Changes of Terms of Service . . . . . . . . . . . . . 35
7.3.5. External Account Binding . . . . . . . . . . . . . . 35 7.3.5. External Account Binding . . . . . . . . . . . . . . 35
7.3.6. Account Key Roll-over . . . . . . . . . . . . . . . . 37 7.3.6. Account Key Roll-over . . . . . . . . . . . . . . . . 37
7.3.7. Account Deactivation . . . . . . . . . . . . . . . . 39 7.3.7. Account Deactivation . . . . . . . . . . . . . . . . 40
7.4. Applying for Certificate Issuance . . . . . . . . . . . . 40 7.4. Applying for Certificate Issuance . . . . . . . . . . . . 41
7.4.1. Pre-Authorization . . . . . . . . . . . . . . . . . . 44 7.4.1. Pre-Authorization . . . . . . . . . . . . . . . . . . 46
7.4.2. Downloading the Certificate . . . . . . . . . . . . . 46 7.4.2. Downloading the Certificate . . . . . . . . . . . . . 48
7.5. Identifier Authorization . . . . . . . . . . . . . . . . 47 7.5. Identifier Authorization . . . . . . . . . . . . . . . . 49
7.5.1. Responding to Challenges . . . . . . . . . . . . . . 48 7.5.1. Responding to Challenges . . . . . . . . . . . . . . 50
7.5.2. Deactivating an Authorization . . . . . . . . . . . . 50 7.5.2. Deactivating an Authorization . . . . . . . . . . . . 52
7.6. Certificate Revocation . . . . . . . . . . . . . . . . . 51 7.6. Certificate Revocation . . . . . . . . . . . . . . . . . 53
8. Identifier Validation Challenges . . . . . . . . . . . . . . 53 8. Identifier Validation Challenges . . . . . . . . . . . . . . 55
8.1. Key Authorizations . . . . . . . . . . . . . . . . . . . 55 8.1. Key Authorizations . . . . . . . . . . . . . . . . . . . 57
8.2. Retrying Challenges . . . . . . . . . . . . . . . . . . . 55 8.2. Retrying Challenges . . . . . . . . . . . . . . . . . . . 57
8.3. HTTP Challenge . . . . . . . . . . . . . . . . . . . . . 56 8.3. HTTP Challenge . . . . . . . . . . . . . . . . . . . . . 58
8.4. DNS Challenge . . . . . . . . . . . . . . . . . . . . . . 58 8.4. DNS Challenge . . . . . . . . . . . . . . . . . . . . . . 60
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
9.1. MIME Type: application/pem-certificate-chain . . . . . . 60 9.1. MIME Type: application/pem-certificate-chain . . . . . . 62
9.2. Well-Known URI for the HTTP Challenge . . . . . . . . . . 61 9.2. Well-Known URI for the HTTP Challenge . . . . . . . . . . 63
9.3. Replay-Nonce HTTP Header . . . . . . . . . . . . . . . . 61 9.3. Replay-Nonce HTTP Header . . . . . . . . . . . . . . . . 63
9.4. "url" JWS Header Parameter . . . . . . . . . . . . . . . 61 9.4. "url" JWS Header Parameter . . . . . . . . . . . . . . . 63
9.5. "nonce" JWS Header Parameter . . . . . . . . . . . . . . 62 9.5. "nonce" JWS Header Parameter . . . . . . . . . . . . . . 64
9.6. URN Sub-namespace for ACME (urn:ietf:params:acme) . . . . 62 9.6. URN Sub-namespace for ACME (urn:ietf:params:acme) . . . . 64
9.7. New Registries . . . . . . . . . . . . . . . . . . . . . 62 9.7. New Registries . . . . . . . . . . . . . . . . . . . . . 64
9.7.1. Fields in Account Objects . . . . . . . . . . . . . . 63 9.7.1. Fields in Account Objects . . . . . . . . . . . . . . 65
9.7.2. Fields in Order Objects . . . . . . . . . . . . . . . 64 9.7.2. Fields in Order Objects . . . . . . . . . . . . . . . 66
9.7.3. Fields in Authorization Objects . . . . . . . . . . . 65 9.7.3. Fields in Authorization Objects . . . . . . . . . . . 67
9.7.4. Error Types . . . . . . . . . . . . . . . . . . . . . 66 9.7.4. Error Types . . . . . . . . . . . . . . . . . . . . . 68
9.7.5. Resource Types . . . . . . . . . . . . . . . . . . . 66 9.7.5. Resource Types . . . . . . . . . . . . . . . . . . . 68
9.7.6. Fields in the "meta" Object within a Directory Object 67 9.7.6. Fields in the "meta" Object within a Directory Object 69
9.7.7. Identifier Types . . . . . . . . . . . . . . . . . . 68 9.7.7. Identifier Types . . . . . . . . . . . . . . . . . . 70
9.7.8. Validation Methods . . . . . . . . . . . . . . . . . 68 9.7.8. Validation Methods . . . . . . . . . . . . . . . . . 70
10. Security Considerations . . . . . . . . . . . . . . . . . . . 69 10. Security Considerations . . . . . . . . . . . . . . . . . . . 72
10.1. Threat Model . . . . . . . . . . . . . . . . . . . . . . 70 10.1. Threat Model . . . . . . . . . . . . . . . . . . . . . . 72
10.2. Integrity of Authorizations . . . . . . . . . . . . . . 71 10.2. Integrity of Authorizations . . . . . . . . . . . . . . 73
10.3. Denial-of-Service Considerations . . . . . . . . . . . . 73 10.3. Denial-of-Service Considerations . . . . . . . . . . . . 77
10.4. Server-Side Request Forgery . . . . . . . . . . . . . . 74 10.4. Server-Side Request Forgery . . . . . . . . . . . . . . 77
10.5. CA Policy Considerations . . . . . . . . . . . . . . . . 74 10.5. CA Policy Considerations . . . . . . . . . . . . . . . . 78
11. Operational Considerations . . . . . . . . . . . . . . . . . 75 11. Operational Considerations . . . . . . . . . . . . . . . . . 79
11.1. Key Selection . . . . . . . . . . . . . . . . . . . . . 75 11.1. Key Selection . . . . . . . . . . . . . . . . . . . . . 79
11.2. DNS security . . . . . . . . . . . . . . . . . . . . . . 76 11.2. DNS security . . . . . . . . . . . . . . . . . . . . . . 80
11.3. Token Entropy . . . . . . . . . . . . . . . . . . . . . 76 11.3. Token Entropy . . . . . . . . . . . . . . . . . . . . . 80
11.4. Malformed Certificate Chains . . . . . . . . . . . . . . 77 11.4. Malformed Certificate Chains . . . . . . . . . . . . . . 81
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 77 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 81
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 78 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 82
13.1. Normative References . . . . . . . . . . . . . . . . . . 78 13.1. Normative References . . . . . . . . . . . . . . . . . . 82
13.2. Informative References . . . . . . . . . . . . . . . . . 80 13.2. Informative References . . . . . . . . . . . . . . . . . 85
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 81 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 86
1. Introduction 1. Introduction
Certificates [RFC5280] in the Web PKI are most commonly used to Certificates [RFC5280] in the Web PKI are most commonly used to
authenticate domain names. Thus, certificate authorities in the Web authenticate domain names. Thus, certificate authorities in the Web
PKI are trusted to verify that an applicant for a certificate PKI are trusted to verify that an applicant for a certificate
legitimately represents the domain name(s) in the certificate. legitimately represents the domain name(s) in the certificate.
Different types of certificates reflect different kinds of CA Different types of certificates reflect different kinds of CA
verification of information about the certificate subject. "Domain verification of information about the certificate subject. "Domain
Validation" (DV) certificates are by far the most common type. For Validation" (DV) certificates are by far the most common type. The
DV validation, the CA merely verifies that the requester has only validation the CA is required to perform in the DV issuance
effective control of the web server and/or DNS server for the domain, process is to verify that the requester has effective control of the
but does not explicitly attempt to verify their real-world identity. domain. The CA is not required to attempt to verify the requester's
(This is as opposed to "Organization Validation" (OV) and "Extended real-world identity. (This is as opposed to "Organization
Validation" (EV) certificates, where the process is intended to also Validation" (OV) and "Extended Validation" (EV) certificates, where
verify the real-world identity of the requester.) the process is intended to also verify the real-world identity of the
requester.)
Existing Web PKI certificate authorities tend to use a set of ad hoc Existing Web PKI certificate authorities tend to use a set of ad hoc
protocols for certificate issuance and identity verification. In the protocols for certificate issuance and identity verification. In the
case of DV certificates, a typical user experience is something like: case of DV certificates, a typical user experience is something like:
o Generate a PKCS#10 [RFC2986] Certificate Signing Request (CSR). o Generate a PKCS#10 [RFC2986] Certificate Signing Request (CSR).
o Cut-and-paste the CSR into a CA web page. o Cut-and-paste the CSR into a CA web page.
o Prove ownership of the domain by one of the following methods: o Prove ownership of the domain by one of the following methods:
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time based on the capabilities of CAs and updates to ACME time based on the capabilities of CAs and updates to ACME
configuration.) The ACME client might prompt the operator for configuration.) The ACME client might prompt the operator for
payment information at this point. payment information at this point.
o The operator selects a CA. o The operator selects a CA.
o In the background, the ACME client contacts the CA and requests o In the background, the ACME client contacts the CA and requests
that it issue a certificate for the intended domain name(s). that it issue a certificate for the intended domain name(s).
o The CA verifies that the client controls the requested domain o The CA verifies that the client controls the requested domain
name(s) by having the ACME client perform some action related to name(s) by having the ACME client perform some action(s) that can
the domain name(s). only be done with control of the domain name(s). For example, the
CA might require a client requesting example.com to provision DNS
record under example.com or an HTTP resource under
http://example.com.
o Once the CA is satisfied, it issues the certificate and the ACME o Once the CA is satisfied, it issues the certificate and the ACME
client automatically downloads and installs it, potentially client automatically downloads and installs it, potentially
notifying the operator via email, SMS, etc. notifying the operator via email, SMS, etc.
o The ACME client periodically contacts the CA to get updated o The ACME client periodically contacts the CA to get updated
certificates, stapled OCSP responses, or whatever else would be certificates, stapled OCSP responses, or whatever else would be
required to keep the web server functional and its credentials up- required to keep the web server functional and its credentials up-
to-date. to-date.
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certificate as with a self-signed certificate. Furthermore, the certificate as with a self-signed certificate. Furthermore, the
maintenance of that CA-issued certificate would require minimal maintenance of that CA-issued certificate would require minimal
manual intervention. Such close integration of ACME with HTTPS manual intervention. Such close integration of ACME with HTTPS
servers allows the immediate and automated deployment of certificates servers allows the immediate and automated deployment of certificates
as they are issued, sparing the human administrator from much of the as they are issued, sparing the human administrator from much of the
time-consuming work described in the previous section. time-consuming work described in the previous section.
3. Terminology 3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "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.
The two main roles in ACME are "client" and "server". The ACME The two main roles in ACME are "client" and "server". The ACME
client uses the protocol to request certificate management actions, client uses the protocol to request certificate management actions,
such as issuance or revocation. An ACME client may run on a web such as issuance or revocation. An ACME client may run on a web
server, mail server, or some other server system which requires valid server, mail server, or some other server system which requires valid
TLS certificates. Or, it may run on a separate server that does not TLS certificates. Or, it may run on a separate server that does not
consume the certificate, but is authorized to respond to a CA- consume the certificate, but is authorized to respond to a CA-
provided challenge. The ACME server runs at a certification provided challenge. The ACME server runs at a certification
authority, and responds to client requests, performing the requested authority, and responds to client requests, performing the requested
actions if the client is authorized. actions if the client is authorized.
An ACME client is represented by an "account key pair". The client An ACME client authenticates to the server by means of an "account
uses the private key of this key pair to sign all messages sent to key pair". The client uses the private key of this key pair to sign
the server. The server uses the public key to verify the all messages sent to the server. The server uses the public key to
authenticity and integrity of messages from the client. verify the authenticity and integrity of messages from the client.
4. Protocol Overview 4. Protocol Overview
ACME allows a client to request certificate management actions using ACME allows a client to request certificate management actions using
a set of JavaScript Object Notation (JSON) messages carried over a set of JavaScript Object Notation (JSON) messages carried over
HTTPS. Issuance using ACME resembles a traditional CA's issuance HTTPS. Issuance using ACME resembles a traditional CA's issuance
process, in which a user creates an account, requests a certificate, process, in which a user creates an account, requests a certificate,
and proves control of the domain(s) in that certificate in order for and proves control of the domain(s) in that certificate in order for
the CA to sign the requested certificate. the CA to sign the requested certificate.
The first phase of ACME is for the client to request an account with The first phase of ACME is for the client to request an account with
the ACME server. The client generates an asymmetric key pair and the ACME server. The client generates an asymmetric key pair and
requests a new account, optionally providing contact information, requests a new account, optionally providing contact information,
agreeing to terms of service, and/or associating the account with an agreeing to terms of service, and/or associating the account with an
existing account in another system. The creation request is signed existing account in another system. The creation request is signed
with the generated private key to prove that the client controls it. with the generated private key to prove that the client controls it.
Client Server Client Server
Contact Information [Contact Information]
ToS Agreement [ToS Agreement]
Additional Data [Additional Data]
Signature -------> Signature ------->
Account URL
<------- Account Object
<------- Account [] Information covered by request signatures
Account Creation
Once an account is registered, there are four major steps the client Once an account is registered, there are four major steps the client
needs to take to get a certificate: needs to take to get a certificate:
1. Submit an order for a certificate to be issued 1. Submit an order for a certificate to be issued
2. Prove control of any identifiers requested in the certificate 2. Prove control of any identifiers requested in the certificate
3. Finalize the order by submitting a CSR 3. Finalize the order by submitting a CSR
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the challenges. the challenges.
Once the validation process is complete and the server is satisfied Once the validation process is complete and the server is satisfied
that the client has met its requirements, the client finalizes the that the client has met its requirements, the client finalizes the
order by submitting a PKCS#10 Certificate Signing Request (CSR). The order by submitting a PKCS#10 Certificate Signing Request (CSR). The
server will issue the requested certificate and make it available to server will issue the requested certificate and make it available to
the client. the client.
Client Server Client Server
Order [Order]
Signature -------> Signature ------->
<------- Required Authorizations <------- Required Authorizations
Responses [Responses]
Signature -------> Signature ------->
<~~~~~~~~Validation~~~~~~~~> <~~~~~~~~Validation~~~~~~~~>
CSR [CSR]
Signature -------> Signature ------->
<------- Acknowledgement
<~~~~~~Await issuance~~~~~~> <~~~~~~Await issuance~~~~~~>
<------- Certificate GET request ------->
<------- Certificate
[] Information covered by request signatures
Certificate Issuance
To revoke a certificate, the client sends a signed revocation request To revoke a certificate, the client sends a signed revocation request
indicating the certificate to be revoked: indicating the certificate to be revoked:
Client Server Client Server
Revocation request [Revocation request]
Signature --------> Signature -------->
<-------- Result <-------- Result
[] Information covered by request signatures
Certificate Revocation
Note that while ACME is defined with enough flexibility to handle Note that while ACME is defined with enough flexibility to handle
different types of identifiers in principle, the primary use case different types of identifiers in principle, the primary use case
addressed by this document is the case where domain names are used as addressed by this document is the case where domain names are used as
identifiers. For example, all of the identifier validation identifiers. For example, all of the identifier validation
challenges described in Section 8 below address validation of domain challenges described in Section 8 below address validation of domain
names. The use of ACME for other identifiers will require further names. The use of ACME for other identifiers will require further
specification in order to describe how these identifiers are encoded specification in order to describe how these identifiers are encoded
in the protocol and what types of validation challenges the server in the protocol and what types of validation challenges the server
might require. might require.
skipping to change at page 10, line 24 skipping to change at page 11, line 9
ACME servers that are intended to be generally accessible need to use ACME servers that are intended to be generally accessible need to use
Cross-Origin Resource Sharing (CORS) in order to be accessible from Cross-Origin Resource Sharing (CORS) in order to be accessible from
browser-based clients [W3C.CR-cors-20130129]. Such servers SHOULD browser-based clients [W3C.CR-cors-20130129]. Such servers SHOULD
set the Access-Control-Allow-Origin header field to the value "*". set the Access-Control-Allow-Origin header field to the value "*".
Binary fields in the JSON objects used by ACME are encoded using Binary fields in the JSON objects used by ACME are encoded using
base64url encoding described in [RFC4648] Section 5, according to the base64url encoding described in [RFC4648] Section 5, according to the
profile specified in JSON Web Signature [RFC7515] Section 2. This profile specified in JSON Web Signature [RFC7515] Section 2. This
encoding uses a URL safe character set. Trailing '=' characters MUST encoding uses a URL safe character set. Trailing '=' characters MUST
be stripped. be stripped. Encoded values that include trailing '=' characters
MUST be rejected as improperly encoded.
6.2. Request Authentication 6.2. Request Authentication
All ACME requests with a non-empty body MUST encapsulate their All ACME requests with a non-empty body MUST encapsulate their
payload in a JSON Web Signature (JWS) [RFC7515] object, signed using payload in a JSON Web Signature (JWS) [RFC7515] object, signed using
the account's private key unless otherwise specified. The server the account's private key unless otherwise specified. The server
MUST verify the JWS before processing the request. Encapsulating MUST verify the JWS before processing the request. Encapsulating
request bodies in JWS provides authentication of requests. request bodies in JWS provides authentication of requests.
JWS objects sent in ACME requests MUST meet the following additional JWS objects sent in ACME requests MUST meet the following additional
criteria: criteria:
o The JWS MUST be in the Flattened JSON Serialization [RFC7515] o The JWS MUST be in the Flattened JSON Serialization [RFC7515]
o The JWS MUST NOT have the value "none" in its "alg" field
o The JWS MUST NOT have multiple signatures o The JWS MUST NOT have multiple signatures
o The JWS Unencoded Payload Option [RFC7797] MUST NOT be used o The JWS Unencoded Payload Option [RFC7797] MUST NOT be used
o The JWS Unprotected Header [RFC7515] MUST NOT be used o The JWS Unprotected Header [RFC7515] MUST NOT be used
o The JWS MUST NOT have a Message Authentication Code (MAC)-based
algorithm in its "alg" field
o The JWS Payload MUST NOT be detached o The JWS Payload MUST NOT be detached
o The JWS Protected Header MUST include the following fields: o The JWS Protected Header MUST include the following fields:
* "alg" (Algorithm) * "alg" (Algorithm)
* "jwk" (JSON Web Key, for all requests not signed using an + This field MUST NOT contain "none" or a Message
existing account, e.g. newAccount) Authentication Code (MAC)-based algorithm
* "kid" (Key ID, for all requests signed using an existing
account)
* "nonce" (defined in Section 6.4 below) * "nonce" (defined in Section 6.4 below)
* "url" (defined in Section 6.3 below) * "url" (defined in Section 6.3 below)
* Either "jwk" (JSON Web Key) or "kid" (Key ID) as specified
below
An ACME server MUST implement the "ES256" signature algorithm
[RFC7518] and SHOULD implement the "EdDSA" signature algorithm using
the "Ed25519" variant (indicated by "crv") [RFC8037].
The "jwk" and "kid" fields are mutually exclusive. Servers MUST The "jwk" and "kid" fields are mutually exclusive. Servers MUST
reject requests that contain both. reject requests that contain both.
For newAccount requests, and for revokeCert requests authenticated by For newAccount requests, and for revokeCert requests authenticated by
certificate key, there MUST be a "jwk" field. This field MUST certificate key, there MUST be a "jwk" field. This field MUST
contain the public key corresponding to the private key used to sign contain the public key corresponding to the private key used to sign
the JWS. the JWS.
For all other requests, the request is signed using an existing For all other requests, the request is signed using an existing
account and there MUST be a "kid" field. This field MUST contain the account and there MUST be a "kid" field. This field MUST contain the
skipping to change at page 11, line 39 skipping to change at page 12, line 23
Note that authentication via signed JWS request bodies implies that Note that authentication via signed JWS request bodies implies that
GET requests are not authenticated. Servers MUST NOT respond to GET GET requests are not authenticated. Servers MUST NOT respond to GET
requests for resources that might be considered sensitive. Account requests for resources that might be considered sensitive. Account
resources are the only sensitive resources defined in this resources are the only sensitive resources defined in this
specification. specification.
If the client sends a JWS signed with an algorithm that the server If the client sends a JWS signed with an algorithm that the server
does not support, then the server MUST return an error with status does not support, then the server MUST return an error with status
code 400 (Bad Request) and type code 400 (Bad Request) and type
"urn:ietf:params:acme:error:badSignatureAlgorithm". The problem "urn:ietf:params:acme:error:badSignatureAlgorithm" (see Section 6.6).
document returned with the error MUST include an "algorithms" field The problem document returned with the error MUST include an
with an array of supported "alg" values. "algorithms" field with an array of supported "alg" values.
Because client requests in ACME carry JWS objects in the Flattened Because client requests in ACME carry JWS objects in the Flattened
JSON Serialization, they must have the "Content-Type" header field JSON Serialization, they must have the "Content-Type" header field
set to "application/jose+json". If a request does not meet this set to "application/jose+json". If a request does not meet this
requirement, then the server MUST return a response with status code requirement, then the server MUST return a response with status code
415 (Unsupported Media Type). 415 (Unsupported Media Type).
6.3. Request URL Integrity 6.3. Request URL Integrity
It is common in deployment for the entity terminating TLS for HTTPS It is common in deployment for the entity terminating TLS for HTTPS
skipping to change at page 19, line 27 skipping to change at page 19, line 46
account | order --+--> finalize account | order --+--> finalize
| | | | | |
| | +--> cert | | +--> cert
| V | V
+---> authorization +---> authorization
| ^ | ^
| | "up" | | "up"
V | V |
challenge challenge
ACME Resources and Relationships
The following table illustrates a typical sequence of requests The following table illustrates a typical sequence of requests
required to establish a new account with the server, prove control of required to establish a new account with the server, prove control of
an identifier, issue a certificate, and fetch an updated certificate an identifier, issue a certificate, and fetch an updated certificate
some time after issuance. The "->" is a mnemonic for a Location some time after issuance. The "->" is a mnemonic for a Location
header pointing to a created resource. header pointing to a created resource.
+-----------------------+--------------------------+----------------+ +-----------------------+--------------------------+----------------+
| Action | Request | Response | | Action | Request | Response |
+-----------------------+--------------------------+----------------+ +-----------------------+--------------------------+----------------+
| Get directory | GET directory | 200 | | Get directory | GET directory | 200 |
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7.1.2. Account Objects 7.1.2. Account Objects
An ACME account resource represents a set of metadata associated with An ACME account resource represents a set of metadata associated with
an account. Account resources have the following structure: an account. Account resources have the following structure:
status (required, string): The status of this account. Possible status (required, string): The status of this account. Possible
values are: "valid", "deactivated", and "revoked". The value values are: "valid", "deactivated", and "revoked". The value
"deactivated" should be used to indicate client-initiated "deactivated" should be used to indicate client-initiated
deactivation whereas "revoked" should be used to indicate server- deactivation whereas "revoked" should be used to indicate server-
initiated deactivation. initiated deactivation. (See Section 7.1.6)
contact (optional, array of string): An array of URLs that the contact (optional, array of string): An array of URLs that the
server can use to contact the client for issues related to this server can use to contact the client for issues related to this
account. For example, the server may wish to notify the client account. For example, the server may wish to notify the client
about server-initiated revocation or certificate expiration. about server-initiated revocation or certificate expiration.
termsOfServiceAgreed (optional, boolean): Including this field in a termsOfServiceAgreed (optional, boolean): Including this field in a
new-account request, with a value of true, indicates the client's new-account request, with a value of true, indicates the client's
agreement with the terms of service. This field is not updateable agreement with the terms of service. This field is not updateable
by the client. by the client.
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7.1.3. Order Objects 7.1.3. Order Objects
An ACME order object represents a client's request for a certificate An ACME order object represents a client's request for a certificate
and is used to track the progress of that order through to issuance. and is used to track the progress of that order through to issuance.
Thus, the object contains information about the requested Thus, the object contains information about the requested
certificate, the authorizations that the server requires the client certificate, the authorizations that the server requires the client
to complete, and any certificates that have resulted from this order. to complete, and any certificates that have resulted from this order.
status (required, string): The status of this order. Possible status (required, string): The status of this order. Possible
values are: "pending", "ready", "processing", "valid", and values are: "pending", "ready", "processing", "valid", and
"invalid". "invalid". (See Section 7.1.6)
expires (optional, string): The timestamp after which the server expires (optional, string): The timestamp after which the server
will consider this order invalid, encoded in the format specified will consider this order invalid, encoded in the format specified
in RFC 3339 [RFC3339]. This field is REQUIRED for objects with in RFC 3339 [RFC3339]. This field is REQUIRED for objects with
"pending" or "valid" in the status field. "pending" or "valid" in the status field.
identifiers (required, array of object): An array of identifier identifiers (required, array of object): An array of identifier
objects that the order pertains to. objects that the order pertains to.
type (required, string): The type of identifier. type (required, string): The type of identifier. This document
defines the "dns" identifier type. See the registry defined in
Section 9.7.7 for any others.
value (required, string): The identifier itself. value (required, string): The identifier itself.
notBefore (optional, string): The requested value of the notBefore notBefore (optional, string): The requested value of the notBefore
field in the certificate, in the date format defined in [RFC3339]. field in the certificate, in the date format defined in [RFC3339].
notAfter (optional, string): The requested value of the notAfter notAfter (optional, string): The requested value of the notAfter
field in the certificate, in the date format defined in [RFC3339]. field in the certificate, in the date format defined in [RFC3339].
error (optional, object): The error that occurred while processing error (optional, object): The error that occurred while processing
the order, if any. This field is structured as a problem document the order, if any. This field is structured as a problem document
[RFC7807]. [RFC7807].
authorizations (required, array of string): For pending orders, the authorizations (required, array of string): For pending orders, the
authorizations that the client needs to complete before the authorizations that the client needs to complete before the
requested certificate can be issued (see Section 7.5). The requested certificate can be issued (see Section 7.5), including
authorizations required are dictated by server policy and there unexpired authorizations that the client has completed in the past
may not be a 1:1 relationship between the order identifiers and for identifiers specified in the order. The authorizations
the authorizations required. For final orders (in the "valid" or required are dictated by server policy and there may not be a 1:1
"invalid" state), the authorizations that were completed. Each relationship between the order identifiers and the authorizations
entry is a URL from which an authorization can be fetched with a required. For final orders (in the "valid" or "invalid" state),
GET request. the authorizations that were completed. Each entry is a URL from
which an authorization can be fetched with a GET request.
finalize (required, string): A URL that a CSR must be POSTed to once finalize (required, string): A URL that a CSR must be POSTed to once
all of the order's authorizations are satisfied to finalize the all of the order's authorizations are satisfied to finalize the
order. The result of a successful finalization will be the order. The result of a successful finalization will be the
population of the certificate URL for the order. population of the certificate URL for the order.
certificate (optional, string): A URL for the certificate that has certificate (optional, string): A URL for the certificate that has
been issued in response to this order. been issued in response to this order.
{ {
skipping to change at page 26, line 5 skipping to change at page 25, line 50
in the contents of either array, then it SHOULD consider the order in the contents of either array, then it SHOULD consider the order
invalid. invalid.
The "authorizations" array of the order SHOULD reflect all The "authorizations" array of the order SHOULD reflect all
authorizations that the CA takes into account in deciding to issue, authorizations that the CA takes into account in deciding to issue,
even if some authorizations were fulfilled in earlier orders or in even if some authorizations were fulfilled in earlier orders or in
pre-authorization transactions. For example, if a CA allows multiple pre-authorization transactions. For example, if a CA allows multiple
orders to be fulfilled based on a single authorization transaction, orders to be fulfilled based on a single authorization transaction,
then it SHOULD reflect that authorization in all of the orders. then it SHOULD reflect that authorization in all of the orders.
Note that just because an authorization URL is listed in the
"authorizations" array of an order object doesn't mean that the
client is required to take action. There are several reasons that
the referenced authorizations may already be valid:
o The client completed the authorization as part of a previous order
o The client previously pre-authorized the identifier (see
Section 7.4.1)
o The server granted the client authorization based on an external
account
Clients should check the "status" field of an order to determine
whether they need to take any action.
7.1.4. Authorization Objects 7.1.4. Authorization Objects
An ACME authorization object represents a server's authorization for An ACME authorization object represents a server's authorization for
an account to represent an identifier. In addition to the an account to represent an identifier. In addition to the
identifier, an authorization includes several metadata fields, such identifier, an authorization includes several metadata fields, such
as the status of the authorization (e.g., "pending", "valid", or as the status of the authorization (e.g., "pending", "valid", or
"revoked") and which challenges were used to validate possession of "revoked") and which challenges were used to validate possession of
the identifier. the identifier.
The structure of an ACME authorization resource is as follows: The structure of an ACME authorization resource is as follows:
identifier (required, object): The identifier that the account is identifier (required, object): The identifier that the account is
authorized to represent authorized to represent
type (required, string): The type of identifier. type (required, string): The type of identifier. (See below and
Section 9.7.7)
value (required, string): The identifier itself. value (required, string): The identifier itself.
status (required, string): The status of this authorization. status (required, string): The status of this authorization.
Possible values are: "pending", "valid", "invalid", "deactivated", Possible values are: "pending", "valid", "invalid", "deactivated",
"expired", and "revoked". "expired", and "revoked". (See Section 7.1.6)
expires (optional, string): The timestamp after which the server expires (optional, string): The timestamp after which the server
will consider this authorization invalid, encoded in the format will consider this authorization invalid, encoded in the format
specified in RFC 3339 [RFC3339]. This field is REQUIRED for specified in RFC 3339 [RFC3339]. This field is REQUIRED for
objects with "valid" in the "status" field. objects with "valid" in the "status" field.
challenges (required, array of objects): For pending authorizations, challenges (required, array of objects): For pending authorizations,
the challenges that the client can fulfill in order to prove the challenges that the client can fulfill in order to prove
possession of the identifier. For final authorizations (in the possession of the identifier. For final authorizations (in the
"valid" or "invalid" state), the challenges that were used. Each "valid" or "invalid" state), the challenges that were used. Each
skipping to change at page 28, line 29 skipping to change at page 28, line 49
| +----+ | +----+
| |
| |
Successful | Failed Successful | Failed
validation | validation validation | validation
+---------+---------+ +---------+---------+
| | | |
V V V V
valid invalid valid invalid
State Transitions for Challenge Objects
Authorization objects are created in the "pending" state. If one of Authorization objects are created in the "pending" state. If one of
the challenges listed in the authorization transitions to the "valid" the challenges listed in the authorization transitions to the "valid"
state, then the authorization also changes to the "valid" state. If state, then the authorization also changes to the "valid" state. If
there is an error while the authorization is still pending, then the there is an error while the authorization is still pending, then the
authorization transitions to the "invalid" state. Once the authorization transitions to the "invalid" state. Once the
authorization is in the valid state, it can expire ("expired"), be authorization is in the valid state, it can expire ("expired"), be
deactivated by the client ("deactivated", see Section 7.5.2), or deactivated by the client ("deactivated", see Section 7.5.2), or
revoked by the server ("revoked"). revoked by the server ("revoked").
pending --------------------+ pending --------------------+
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| | | |
| | | |
+--------------+--------------+ +--------------+--------------+
| | | | | |
| | | | | |
Server | Client | Time after | Server | Client | Time after |
revoke | deactivate | "expires" | revoke | deactivate | "expires" |
V V V V V V
revoked deactivated expired revoked deactivated expired
State Transitions for Authorization Objects
Order objects are created in the "pending" state. Once all of the Order objects are created in the "pending" state. Once all of the
authorizations listed in the order object are in the "valid" state, authorizations listed in the order object are in the "valid" state,
the order transitions to the "ready" state. The order moves to the the order transitions to the "ready" state. The order moves to the
"processing" state after the client submits a request to the order's "processing" state after the client submits a request to the order's
"finalize" URL and the CA begins the issuance process for the "finalize" URL and the CA begins the issuance process for the
certificate. Once the certificate is issued, the order enters the certificate. Once the certificate is issued, the order enters the
"valid" state. If an error occurs at any of these stages, the order "valid" state. If an error occurs at any of these stages, the order
moves to the "invalid" state. The order also moves to the "invalid" moves to the "invalid" state. The order also moves to the "invalid"
state if it expires, or one of its authorizations enters a final state if it expires, or one of its authorizations enters a final
state other than "valid" ("expired", "revoked", "deactivated"). state other than "valid" ("expired", "revoked", "deactivated").
skipping to change at page 30, line 5 skipping to change at page 30, line 23
| finalize | | finalize |
| request | | request |
V | V |
processing ------------+ processing ------------+
| | | |
| Certificate | Error or | Certificate | Error or
| issued | Authorization failure | issued | Authorization failure
V V V V
valid invalid valid invalid
State Transitions for Order Objects
Account objects are created in the "valid" state, since no further Account objects are created in the "valid" state, since no further
action is required to create an account after a successful newAccount action is required to create an account after a successful newAccount
request. If the account is deactivated by the client or revoked by request. If the account is deactivated by the client or revoked by
the server, it moves to the corresponding state. the server, it moves to the corresponding state.
valid valid
| |
| |
+-----------+-----------+ +-----------+-----------+
Client | Server | Client | Server |
deactiv.| revoke | deactiv.| revoke |
V V V V
deactivated revoked deactivated revoked
State Transitions for Account Objects
Note that some of these states may not ever appear in a "status" Note that some of these states may not ever appear in a "status"
field, depending on server behavior. For example, a server that field, depending on server behavior. For example, a server that
issues synchronously will never show an order in the "processing" issues synchronously will never show an order in the "processing"
state. A server that deletes expired authorizations immediately will state. A server that deletes expired authorizations immediately will
never show an authorization in the "expired" state. never show an authorization in the "expired" state.
7.2. Getting a Nonce 7.2. Getting a Nonce
Before sending a POST request to the server, an ACME client needs to Before sending a POST request to the server, an ACME client needs to
have a fresh anti-replay nonce to put in the "nonce" header of the have a fresh anti-replay nonce to put in the "nonce" header of the
JWS. In most cases, the client will have gotten a nonce from a JWS. In most cases, the client will have gotten a nonce from a
previous request. However, the client might sometimes need to get a previous request. However, the client might sometimes need to get a
new nonce, e.g., on its first request to the server or if an existing new nonce, e.g., on its first request to the server or if an existing
nonce is no longer valid. nonce is no longer valid.
To get a fresh nonce, the client sends a HEAD request to the new- To get a fresh nonce, the client sends a HEAD request to the new-
nonce resource on the server. The server's response MUST include a nonce resource on the server. The server's response MUST include a
Replay-Nonce header field containing a fresh nonce, and SHOULD have Replay-Nonce header field containing a fresh nonce, and SHOULD have
status code 200 (OK). The server SHOULD also respond to GET requests status code 200 (OK). The server MUST also respond to GET requests
for this resource, returning an empty body (while still providing a for this resource, returning an empty body (while still providing a
Replay-Nonce header) with a 204 (No Content) status. Replay-Nonce header) with a 204 (No Content) status.
HEAD /acme/new-nonce HTTP/1.1 HEAD /acme/new-nonce HTTP/1.1
Host: example.com Host: example.com
HTTP/1.1 200 OK HTTP/1.1 200 OK
Replay-Nonce: oFvnlFP1wIhRlYS2jTaXbA Replay-Nonce: oFvnlFP1wIhRlYS2jTaXbA
Cache-Control: no-store Cache-Control: no-store
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"contact": [ "contact": [
"mailto:cert-admin@example.com", "mailto:cert-admin@example.com",
"mailto:admin@example.com" "mailto:admin@example.com"
], ],
"orders": "https://example.com/acme/acct/1/orders" "orders": "https://example.com/acme/acct/1/orders"
} }
7.3.1. Finding an Account URL Given a Key 7.3.1. Finding an Account URL Given a Key
If the server already has an account registered with the provided If the server receives a newAccount request signed with a key for
account key, then it MUST return a response with a 200 (OK) status which it already has an account registered with the provided account
code and provide the URL of that account in the Location header key, then it MUST return a response with a 200 (OK) status code and
field. This allows a client that has an account key but not the provide the URL of that account in the Location header field. The
body of this response represents the account object as it existed on
the server before this request; any fields in the request object MUST
be ignored. This allows a client that has an account key but not the
corresponding account URL to recover the account URL. corresponding account URL to recover the account URL.
If a client wishes to find the URL for an existing account and does If a client wishes to find the URL for an existing account and does
not want an account to be created if one does not already exist, then not want an account to be created if one does not already exist, then
it SHOULD do so by sending a POST request to the new-account URL with it SHOULD do so by sending a POST request to the new-account URL with
a JWS whose payload has an "onlyReturnExisting" field set to "true" a JWS whose payload has an "onlyReturnExisting" field set to "true"
({"onlyReturnExisting": true}). If a client sends such a request and ({"onlyReturnExisting": true}). If a client sends such a request and
an account does not exist, then the server MUST return an error an account does not exist, then the server MUST return an error
response with status code 400 (Bad Request) and type response with status code 400 (Bad Request) and type
"urn:ietf:params:acme:error:accountDoesNotExist". "urn:ietf:params:acme:error:accountDoesNotExist".
7.3.2. Account Update 7.3.2. Account Update
If the client wishes to update this information in the future, it If the client wishes to update this information in the future, it
sends a POST request with updated information to the account URL. sends a POST request with updated information to the account URL.
The server MUST ignore any updates to the "orders" field or any other The server MUST ignore any updates to the "orders" field,
fields it does not recognize. If the server accepts the update, it "termsOfServiceAgreed" field (see Section 7.3.4), or any other fields
MUST return a response with a 200 (OK) status code and the resulting it does not recognize. If the server accepts the update, it MUST
return a response with a 200 (OK) status code and the resulting
account object. account object.
For example, to update the contact information in the above account, For example, to update the contact information in the above account,
the client could send the following request: the client could send the following request:
POST /acme/acct/1 HTTP/1.1 POST /acme/acct/1 HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/jose+json Content-Type: application/jose+json
{ {
skipping to change at page 37, line 13 skipping to change at page 37, line 27
"kid" field "kid" field
4. Verify that the MAC on the JWS verifies using that MAC key 4. Verify that the MAC on the JWS verifies using that MAC key
5. Verify that the payload of the JWS represents the same key as was 5. Verify that the payload of the JWS represents the same key as was
used to verify the outer JWS (i.e., the "jwk" field of the outer used to verify the outer JWS (i.e., the "jwk" field of the outer
JWS) JWS)
If all of these checks pass and the CA creates a new account, then If all of these checks pass and the CA creates a new account, then
the CA may consider the new account associated with the external the CA may consider the new account associated with the external
account corresponding to the MAC key and MUST reflect the value of account corresponding to the MAC key. The account object the CA
the "externalAccountBinding" field in the resulting account object. returns MUST include an "externalAccountBinding" field with the same
If any of these checks fail, then the CA MUST reject the new-account value as the field in the request. If any of these checks fail, then
request. the CA MUST reject the new-account request.
7.3.6. Account Key Roll-over 7.3.6. Account Key Roll-over
A client may wish to change the public key that is associated with an A client may wish to change the public key that is associated with an
account in order to recover from a key compromise or proactively account in order to recover from a key compromise or proactively
mitigate the impact of an unnoticed key compromise. mitigate the impact of an unnoticed key compromise.
To change the key associated with an account, the client first To change the key associated with an account, the client sends a
constructs a key-change object describing the change that it would request to the server containing signatures by both the old and new
like the server to make: keys. The signature by the new key covers the account URL and the
old key, signifying a request by the new key holder to take over the
account from the old key holder. The signature by the old key covers
this request and its signature, and indicates the old key holder's
assent to the roll-over request.
To create this request object, the client first constructs a key-
change object describing the account to be updated and its account
key:
account (required, string): The URL for the account being modified. account (required, string): The URL for the account being modified.
The content of this field MUST be the exact string provided in the The content of this field MUST be the exact string provided in the
Location header field in response to the new-account request that Location header field in response to the new-account request that
created the account. created the account.
newKey (required, JWK): The JWK representation of the new key oldKey (required, JWK): The JWK representation of the old key
The client then encapsulates the key-change object in an "inner" JWS, The client then encapsulates the key-change object in an "inner" JWS,
signed with the requested new account key (i.e., the key matching the signed with the requested new account key. This "inner" JWS becomes
"newKey" value). This JWS then becomes the payload for the "outer" the payload for the "outer" JWS that is the body of the ACME request.
JWS that is the body of the ACME request.
The outer JWS MUST meet the normal requirements for an ACME JWS (see The outer JWS MUST meet the normal requirements for an ACME JWS (see
Section 6.2). The inner JWS MUST meet the normal requirements, with Section 6.2). The inner JWS MUST meet the normal requirements, with
the following differences: the following differences:
o The inner JWS MUST have a "jwk" header parameter, containing the o The inner JWS MUST have a "jwk" header parameter, containing the
public key of the new key pair (i.e., the same value as the public key of the new key pair.
"newKey" field).
o The inner JWS MUST have the same "url" header parameter as the o The inner JWS MUST have the same "url" header parameter as the
outer JWS. outer JWS.
o The inner JWS is NOT REQUIRED to have a "nonce" header parameter. o The inner JWS is NOT REQUIRED to have a "nonce" header parameter.
The server MUST ignore any value provided for the "nonce" header The server MUST ignore any value provided for the "nonce" header
parameter. parameter.
This transaction has signatures from both the old and new keys so This transaction has signatures from both the old and new keys so
that the server can verify that the holders of the two keys both that the server can verify that the holders of the two keys both
agree to the change. The signatures are nested to preserve the agree to the change. The signatures are nested to preserve the
property that all signatures on POST messages are signed by exactly property that all signatures on POST messages are signed by exactly
one key. one key. The "inner" JWS effectively represents a request by the
holder of the new key to take over the account form the holder of the
old key. The "outer" JWS represents the current account holder's
assent to this request.
POST /acme/key-change HTTP/1.1 POST /acme/key-change HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/jose+json Content-Type: application/jose+json
{ {
"protected": base64url({ "protected": base64url({
"alg": "ES256", "alg": "ES256",
"kid": "https://example.com/acme/acct/1", "kid": "https://example.com/acme/acct/1",
"nonce": "K60BWPrMQG9SDxBDS_xtSw", "nonce": "K60BWPrMQG9SDxBDS_xtSw",
"url": "https://example.com/acme/key-change" "url": "https://example.com/acme/key-change"
}), }),
"payload": base64url({ "payload": base64url({
"protected": base64url({ "protected": base64url({
"alg": "ES256", "alg": "ES256",
"jwk": /* new key */, "jwk": /* new key */,
"url": "https://example.com/acme/key-change" "url": "https://example.com/acme/key-change"
}), }),
"payload": base64url({ "payload": base64url({
"account": "https://example.com/acme/acct/1", "account": "https://example.com/acme/acct/1",
"newKey": /* new key */ "oldKey": /* old key */
}), }),
"signature": "Xe8B94RD30Azj2ea...8BmZIRtcSKPSd8gU" "signature": "Xe8B94RD30Azj2ea...8BmZIRtcSKPSd8gU"
}), }),
"signature": "5TWiqIYQfIDfALQv...x9C2mg8JGPxl5bI4" "signature": "5TWiqIYQfIDfALQv...x9C2mg8JGPxl5bI4"
} }
On receiving key-change request, the server MUST perform the On receiving key-change request, the server MUST perform the
following steps in addition to the typical JWS validation: following steps in addition to the typical JWS validation:
1. Validate the POST request belongs to a currently active account, 1. Validate the POST request belongs to a currently active account,
skipping to change at page 39, line 15 skipping to change at page 40, line 6
4. Check that the inner JWS verifies using the key in its "jwk" 4. Check that the inner JWS verifies using the key in its "jwk"
field. field.
5. Check that the payload of the inner JWS is a well-formed key- 5. Check that the payload of the inner JWS is a well-formed key-
change object (as described above). change object (as described above).
6. Check that the "url" parameters of the inner and outer JWSs are 6. Check that the "url" parameters of the inner and outer JWSs are
the same. the same.
7. Check that the "account" field of the key-change object contains 7. Check that the "account" field of the key-change object contains
the URL for the account matching the old key. the URL for the account matching the old key (i.e., the "kid"
field in the outer JWS).
8. Check that the "newKey" field of the key-change object also 8. Check that the "oldKey" field of the key-change object is the
verifies the inner JWS. same as the account key for the account in question.
9. Check that no account exists whose account key is the same as the 9. Check that no account exists whose account key is the same as the
key in the "newKey" field. key in the "jwk" header parameter of the inner JWS.
If all of these checks pass, then the server updates the If all of these checks pass, then the server updates the
corresponding account by replacing the old account key with the new corresponding account by replacing the old account key with the new
public key and returns status code 200 (OK). Otherwise, the server public key and returns status code 200 (OK). Otherwise, the server
responds with an error status code and a problem document describing responds with an error status code and a problem document describing
the error. If there is an existing account with the new key the error. If there is an existing account with the new key
provided, then the server SHOULD use status code 409 (Conflict) and provided, then the server SHOULD use status code 409 (Conflict) and
provide the URL of that account in the Location header field. provide the URL of that account in the Location header field.
Note that changing the account key for an account SHOULD NOT have any Note that changing the account key for an account SHOULD NOT have any
skipping to change at page 40, line 39 skipping to change at page 41, line 21
certificate orders. A server may take a variety of actions in certificate orders. A server may take a variety of actions in
response to an account deactivation, e.g., deleting data related to response to an account deactivation, e.g., deleting data related to
that account or sending mail to the account's contacts. Servers that account or sending mail to the account's contacts. Servers
SHOULD NOT revoke certificates issued by the deactivated account, SHOULD NOT revoke certificates issued by the deactivated account,
since this could cause operational disruption for servers using these since this could cause operational disruption for servers using these
certificates. ACME does not provide a way to reactivate a certificates. ACME does not provide a way to reactivate a
deactivated account. deactivated account.
7.4. Applying for Certificate Issuance 7.4. Applying for Certificate Issuance
The client requests certificate issuance by sending a POST request to The client begins the certificate issuance process by sending a POST
the server's new-order resource. The body of the POST is a JWS request to the server's new-order resource. The body of the POST is
object whose JSON payload is a subset of the order object defined in a JWS object whose JSON payload is a subset of the order object
Section 7.1.3, containing the fields that describe the certificate to defined in Section 7.1.3, containing the fields that describe the
be issued: certificate to be issued:
identifiers (required, array of object): An array of identifier identifiers (required, array of object): An array of identifier
objects that the client wishes to submit an order for. objects that the client wishes to submit an order for.
type (required, string): The type of identifier. type (required, string): The type of identifier.
value (required, string): The identifier itself. value (required, string): The identifier itself.
notBefore (optional, string): The requested value of the notBefore notBefore (optional, string): The requested value of the notBefore
field in the certificate, in the date format defined in [RFC3339]. field in the certificate, in the date format defined in [RFC3339].
skipping to change at page 43, line 24 skipping to change at page 44, line 24
"url": "https://example.com/acme/order/asdf/finalize" "url": "https://example.com/acme/order/asdf/finalize"
}), }),
"payload": base64url({ "payload": base64url({
"csr": "MIIBPTCBxAIBADBFMQ...FS6aKdZeGsysoCo4H9P", "csr": "MIIBPTCBxAIBADBFMQ...FS6aKdZeGsysoCo4H9P",
}), }),
"signature": "uOrUfIIk5RyQ...nw62Ay1cl6AB" "signature": "uOrUfIIk5RyQ...nw62Ay1cl6AB"
} }
The CSR encodes the client's requests with regard to the content of The CSR encodes the client's requests with regard to the content of
the certificate to be issued. The CSR MUST indicate the exact same the certificate to be issued. The CSR MUST indicate the exact same
set of requested identifiers as the initial new-order request, either set of requested identifiers as the initial new-order request.
in the commonName portion of the requested subject name, or in an Identifiers of type "dns" MUST appear either in the commonName
extensionRequest attribute [RFC2985] requesting a subjectAltName portion of the requested subject name, or in an extensionRequest
extension. attribute [RFC2985] requesting a subjectAltName extension. (These
identifiers may appear in any sort order.) Specifications that
define new identifier types must specify where in the certificate
signing request these identifiers can appear.
A request to finalize an order will result in error if the order A request to finalize an order will result in error if the CA is
indicated does not have status "ready", if the CSR and order unwilling to issue a certificate corresponding to the submitted CSR.
identifiers differ, or if the account is not authorized for the For example:
identifiers indicated in the CSR.
o If the order indicated does not have status "ready"
o If the CSR and order identifiers differ
o If the account is not authorized for the identifiers indicated in
the CSR
o If the CSR requests extensions that the CA is not willing to
include
In such cases, the problem document returned by the server SHOULD use
error code "badCSR", and describe specific reasons the CSR was
rejected in its "details" field. After returning such an error, the
server SHOULD leave the order in the "ready" state, to allow the
client to submit a new finalize request with an amended CSR.
A valid request to finalize an order will return the order to be A valid request to finalize an order will return the order to be
finalized. The client should begin polling the order by sending a finalized. The client should begin polling the order by sending a
GET request to the order resource to obtain its current state. The GET request to the order resource to obtain its current state. The
status of the order will indicate what action the client should take: status of the order will indicate what action the client should take:
o "invalid": The certificate will not be issued. Consider this o "invalid": The certificate will not be issued. Consider this
order process abandoned. order process abandoned.
o "pending": The server does not believe that the client has o "pending": The server does not believe that the client has
skipping to change at page 46, line 25 skipping to change at page 48, line 20
header field, and the JSON authorization object in the body. The header field, and the JSON authorization object in the body. The
client then follows the process described in Section 7.5 to complete client then follows the process described in Section 7.5 to complete
the authorization process. the authorization process.
7.4.2. Downloading the Certificate 7.4.2. Downloading the Certificate
To download the issued certificate, the client simply sends a GET To download the issued certificate, the client simply sends a GET
request to the certificate URL. request to the certificate URL.
The default format of the certificate is application/pem-certificate- The default format of the certificate is application/pem-certificate-
chain (see IANA Considerations). chain (see Section 9).
The server MAY provide one or more link relation header fields The server MAY provide one or more link relation header fields
[RFC5988] with relation "alternate". Each such field SHOULD express [RFC5988] with relation "alternate". Each such field SHOULD express
an alternative certificate chain starting with the same end-entity an alternative certificate chain starting with the same end-entity
certificate. This can be used to express paths to various trust certificate. This can be used to express paths to various trust
anchors. Clients can fetch these alternates and use their own anchors. Clients can fetch these alternates and use their own
heuristics to decide which is optimal. heuristics to decide which is optimal.
GET /acme/cert/asdf HTTP/1.1 GET /acme/cert/asdf HTTP/1.1
Host: example.com Host: example.com
skipping to change at page 54, line 32 skipping to change at page 56, line 32
of an identifier of an identifier
Challenge objects all contain the following basic fields: Challenge objects all contain the following basic fields:
type (required, string): The type of challenge encoded in the type (required, string): The type of challenge encoded in the
object. object.
url (required, string): The URL to which a response can be posted. url (required, string): The URL to which a response can be posted.
status (required, string): The status of this challenge. Possible status (required, string): The status of this challenge. Possible
values are: "pending", "processing", "valid", and "invalid". values are: "pending", "processing", "valid", and "invalid". (See
Section 7.1.6)
validated (optional, string): The time at which the server validated validated (optional, string): The time at which the server validated
this challenge, encoded in the format specified in RFC 3339 this challenge, encoded in the format specified in RFC 3339
[RFC3339]. This field is REQUIRED if the "status" field is [RFC3339]. This field is REQUIRED if the "status" field is
"valid". "valid".
error (optional, object): Error that occurred while the server was error (optional, object): Error that occurred while the server was
validating the challenge, if any, structured as a problem document validating the challenge, if any, structured as a problem document
[RFC7807]. Multiple errors can be indicated by using subproblems [RFC7807]. Multiple errors can be indicated by using subproblems
Section 6.6.1. Section 6.6.1.
skipping to change at page 69, line 36 skipping to change at page 71, line 36
| tls-sni-02 | RESERVED | N | RFC XXXX | | tls-sni-02 | RESERVED | N | RFC XXXX |
+------------+-----------------+------+-----------+ +------------+-----------------+------+-----------+
When evaluating a request for an assignment in this registry, the When evaluating a request for an assignment in this registry, the
designated expert should ensure that the method being registered has designated expert should ensure that the method being registered has
a clear, interoperable definition and does not overlap with existing a clear, interoperable definition and does not overlap with existing
validation methods. That is, it should not be possible for a client validation methods. That is, it should not be possible for a client
and server to follow the same set of actions to fulfill two different and server to follow the same set of actions to fulfill two different
validation methods. validation methods.
The values "tls-sni-01" and "tls-sni-02" are reserved because they
were used in pre-RFC versions of this specification to denote
validation methods that were removed because they were found not to
be secure in some cases.
Validation methods do not have to be compatible with ACME in order to Validation methods do not have to be compatible with ACME in order to
be registered. For example, a CA might wish to register a validation be registered. For example, a CA might wish to register a validation
method in order to support its use with the ACME extensions to CAA method in order to support its use with the ACME extensions to CAA
[I-D.ietf-acme-caa]. [I-D.ietf-acme-caa].
[[ RFC EDITOR: Please replace XXXX above with the RFC number assigned [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
to this document ]] to this document ]]
10. Security Considerations 10. Security Considerations
skipping to change at page 70, line 43 skipping to change at page 73, line 19
V V
+------------+ +------------+
| ACME | | ACME |
| Server | | Server |
+------------+ +------------+
+------------+ | +------------+ |
| Validation |<-------------------+ | Validation |<-------------------+
| Server | Validation Channel | Server | Validation Channel
+------------+ +------------+
Communications Channels Used by ACME
In practice, the risks to these channels are not entirely separate, In practice, the risks to these channels are not entirely separate,
but they are different in most cases. Each channel, for example, but they are different in most cases. Each channel, for example,
uses a different communications pattern: the ACME channel will uses a different communications pattern: the ACME channel will
comprise inbound HTTPS connections to the ACME server and the comprise inbound HTTPS connections to the ACME server and the
validation channel outbound HTTP or DNS requests. validation channel outbound HTTP or DNS requests.
Broadly speaking, ACME aims to be secure against active and passive Broadly speaking, ACME aims to be secure against active and passive
attackers on any individual channel. Some vulnerabilities arise attackers on any individual channel. Some vulnerabilities arise
(noted below) when an attacker can exploit both the ACME channel and (noted below) when an attacker can exploit both the ACME channel and
one of the others. one of the others.
skipping to change at page 71, line 25 skipping to change at page 73, line 52
10.2. Integrity of Authorizations 10.2. Integrity of Authorizations
ACME allows anyone to request challenges for an identifier by ACME allows anyone to request challenges for an identifier by
registering an account key and sending a new-order request using that registering an account key and sending a new-order request using that
account key. The integrity of the authorization process thus depends account key. The integrity of the authorization process thus depends
on the identifier validation challenges to ensure that the challenge on the identifier validation challenges to ensure that the challenge
can only be completed by someone who both (1) holds the private key can only be completed by someone who both (1) holds the private key
of the account key pair, and (2) controls the identifier in question. of the account key pair, and (2) controls the identifier in question.
Validation responses need to be bound to an account key pair in order Validation responses need to be bound to an account key pair in order
to avoid situations where an ACME MitM can switch out a legitimate to avoid situations where a MitM on ACME HTTPS requests can switch
domain holder's account key for one of his choosing, e.g.: out a legitimate domain holder's account key for one of his choosing,
e.g.:
o Legitimate domain holder registers account key pair A o Legitimate domain holder registers account key pair A
o MitM registers account key pair B o MitM registers account key pair B
o Legitimate domain holder sends a new-order request signed using o Legitimate domain holder sends a new-order request signed using
account key A account key A
o MitM suppresses the legitimate request but sends the same request o MitM suppresses the legitimate request but sends the same request
signed using account key B signed using account key B
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o Legitimate domain holder provisions the validation response o Legitimate domain holder provisions the validation response
o ACME server performs validation query and sees the response o ACME server performs validation query and sees the response
provisioned by the legitimate domain holder provisioned by the legitimate domain holder
o Because the challenges were issued in response to a message signed o Because the challenges were issued in response to a message signed
account key B, the ACME server grants authorization to account key account key B, the ACME server grants authorization to account key
B (the MitM) instead of account key A (the legitimate domain B (the MitM) instead of account key A (the legitimate domain
holder) holder)
Domain ACME
Holder MitM Server
| | |
| newAccount(A) | |
|--------------------->|--------------------->|
| | |
| | newAccount(B) |
| |--------------------->|
| newOrder(domain, A) | |
|--------------------->| |
| | newOrder(domain, B) |
| |--------------------->|
| | |
| authz, challenges | authz, challenges |
|<---------------------|<---------------------|
| | |
| response(chall, A) | response(chall, B) |
|--------------------->|--------------------->|
| | |
| validation request | |
|<--------------------------------------------|
| | |
| validation response | |
|-------------------------------------------->|
| | |
| | | Considers challenge
| | | fulfilled by B.
| | |
Man-in-the-Middle Attack Exploiting a Validation Method without
Account Key Binding
All of the challenges above have a binding between the account All of the challenges above have a binding between the account
private key and the validation query made by the server, via the key private key and the validation query made by the server, via the key
authorization. The key authorization reflects the account public authorization. The key authorization reflects the account public
key, is provided to the server in the validation response over the key, is provided to the server in the validation response over the
validation channel and signed afterwards by the corresponding private validation channel and signed afterwards by the corresponding private
key in the challenge response over the ACME channel. key in the challenge response over the ACME channel.
The association of challenges to identifiers is typically done by The association of challenges to identifiers is typically done by
requiring the client to perform some action that only someone who requiring the client to perform some action that only someone who
effectively controls the identifier can perform. For the challenges effectively controls the identifier can perform. For the challenges
skipping to change at page 74, line 24 skipping to change at page 78, line 11
URL. In the ACME HTTP challenge validation process, the ACME server URL. In the ACME HTTP challenge validation process, the ACME server
performs an HTTP GET request to a URL in which the attacker can performs an HTTP GET request to a URL in which the attacker can
choose the domain. This request is made before the server has choose the domain. This request is made before the server has
verified that the client controls the domain, so any client can cause verified that the client controls the domain, so any client can cause
a query to any domain. a query to any domain.
Some server implementations include information from the validation Some server implementations include information from the validation
server's response (in order to facilitate debugging). Such server's response (in order to facilitate debugging). Such
implementations enable an attacker to extract this information from implementations enable an attacker to extract this information from
any web server that is accessible to the ACME server, even if it is any web server that is accessible to the ACME server, even if it is
not accessible to the ACME client. not accessible to the ACME client. For example, the ACME server
might be able to access servers behind a firewall that would prevent
access by the ACME client.
It might seem that the risk of SSRF through this channel is limited It might seem that the risk of SSRF through this channel is limited
by the fact that the attacker can only control the domain of the URL, by the fact that the attacker can only control the domain of the URL,
not the path. However, if the attacker first sets the domain to one not the path. However, if the attacker first sets the domain to one
they control, then they can send the server an HTTP redirect (e.g., a they control, then they can send the server an HTTP redirect (e.g., a
302 response) which will cause the server to query an arbitrary URL. 302 response) which will cause the server to query an arbitrary URL.
In order to further limit the SSRF risk, ACME server operators should In order to further limit the SSRF risk, ACME server operators should
ensure that validation queries can only be sent to servers on the ensure that validation queries can only be sent to servers on the
public Internet, and not, say, web services within the server public Internet, and not, say, web services within the server
skipping to change at page 76, line 19 skipping to change at page 80, line 9
legitimate account holder legitimate account holder
For this reason, it is RECOMMENDED that account key pairs be used for For this reason, it is RECOMMENDED that account key pairs be used for
no other purpose besides ACME authentication. For example, the no other purpose besides ACME authentication. For example, the
public key of an account key pair SHOULD NOT be included in a public key of an account key pair SHOULD NOT be included in a
certificate. ACME clients and servers SHOULD verify that a CSR certificate. ACME clients and servers SHOULD verify that a CSR
submitted in a finalize request does not contain a public key for any submitted in a finalize request does not contain a public key for any
known account key pair. In particular, when a server receives a known account key pair. In particular, when a server receives a
finalize request, it MUST verify that the public key in a CSR is not finalize request, it MUST verify that the public key in a CSR is not
the same as the public key of the account key pair used to the same as the public key of the account key pair used to
authenticate that request. authenticate that request. This assures that vulnerabilities in the
protocols with which the certificate is used (e.g., signing oracles
in TLS [JSS15]) do not result in compromise of the ACME account.
11.2. DNS security 11.2. DNS security
As noted above, DNS forgery attacks against the ACME server can As noted above, DNS forgery attacks against the ACME server can
result in the server making incorrect decisions about domain control result in the server making incorrect decisions about domain control
and thus mis-issuing certificates. Servers SHOULD perform DNS and thus mis-issuing certificates. Servers SHOULD perform DNS
queries over TCP, which provides better resistance to some forgery queries over TCP, which provides better resistance to some forgery
attacks than DNS over UDP. attacks than DNS over UDP.
An ACME-based CA will often need to make DNS queries, e.g., to An ACME-based CA will often need to make DNS queries, e.g., to
skipping to change at page 77, line 35 skipping to change at page 81, line 30
certificates. If anything other than a certificate is found (i.e., certificates. If anything other than a certificate is found (i.e.,
if the string "-----BEGIN" is ever followed by anything other than if the string "-----BEGIN" is ever followed by anything other than
"CERTIFICATE"), then the client MUST reject the file as invalid. "CERTIFICATE"), then the client MUST reject the file as invalid.
12. Acknowledgements 12. Acknowledgements
In addition to the editors listed on the front page, this document In addition to the editors listed on the front page, this document
has benefited from contributions from a broad set of contributors, has benefited from contributions from a broad set of contributors,
all the way back to its inception. all the way back to its inception.
o Andrew Ayer, SSLMate
o Karthik Bhargavan, INRIA
o Peter Eckersley, EFF o Peter Eckersley, EFF
o Alex Halderman, University of Michigan
o Sophie Herold, Hemio
o Eric Rescorla, Mozilla o Eric Rescorla, Mozilla
o Seth Schoen, EFF o Seth Schoen, EFF
o Alex Halderman, University of Michigan
o Martin Thomson, Mozilla o Martin Thomson, Mozilla
o Jakub Warmuz, University of Oxford o Jakub Warmuz, University of Oxford
o Sophie Herold, Hemio
This document draws on many concepts established by Eric Rescorla's This document draws on many concepts established by Eric Rescorla's
"Automated Certificate Issuance Protocol" draft. Martin Thomson "Automated Certificate Issuance Protocol" draft. Martin Thomson
provided helpful guidance in the use of HTTP. provided helpful guidance in the use of HTTP.
13. References 13. References
13.1. Normative References 13.1. Normative References
[FIPS180-4] [FIPS180-4]
Department of Commerce, National., "NIST FIPS 180-4, Department of Commerce, National., "NIST FIPS 180-4,
Secure Hash Standard", March 2012, Secure Hash Standard", March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/ <http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>. fips-180-4.pdf>.
[JSS15] Somorovsky, J., "On the Security of TLS 1.3 and QUIC
Against Weaknesses in PKCS#1 v1.5 Encryption", n.d.,
<https://dl.acm.org/citation.cfm?id=2813657>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key [RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP", Infrastructure Operational Protocols: FTP and HTTP",
RFC 2585, DOI 10.17487/RFC2585, May 1999, RFC 2585, DOI 10.17487/RFC2585, May 1999,
<https://www.rfc-editor.org/info/rfc2585>. <https://www.rfc-editor.org/info/rfc2585>.
skipping to change at page 80, line 34 skipping to change at page 84, line 38
2015, <https://www.rfc-editor.org/info/rfc7638>. 2015, <https://www.rfc-editor.org/info/rfc7638>.
[RFC7797] Jones, M., "JSON Web Signature (JWS) Unencoded Payload [RFC7797] Jones, M., "JSON Web Signature (JWS) Unencoded Payload
Option", RFC 7797, DOI 10.17487/RFC7797, February 2016, Option", RFC 7797, DOI 10.17487/RFC7797, February 2016,
<https://www.rfc-editor.org/info/rfc7797>. <https://www.rfc-editor.org/info/rfc7797>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/info/rfc7807>. <https://www.rfc-editor.org/info/rfc7807>.
[RFC8037] Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH)
and Signatures in JSON Object Signing and Encryption
(JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017,
<https://www.rfc-editor.org/info/rfc8037>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[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>.
13.2. Informative References 13.2. Informative References
[I-D.ietf-acme-caa] [I-D.ietf-acme-caa]
Landau, H., "CAA Record Extensions for Account URI and Landau, H., "CAA Record Extensions for Account URI and
ACME Method Binding", draft-ietf-acme-caa-03 (work in ACME Method Binding", draft-ietf-acme-caa-05 (work in
progress), August 2017. progress), June 2018.
[I-D.ietf-acme-ip] [I-D.ietf-acme-ip]
Shoemaker, R., "ACME IP Identifier Validation Extension", Shoemaker, R., "ACME IP Identifier Validation Extension",
draft-ietf-acme-ip-01 (work in progress), September 2017. draft-ietf-acme-ip-02 (work in progress), May 2018.
[I-D.ietf-acme-telephone] [I-D.ietf-acme-telephone]
Peterson, J. and R. Barnes, "ACME Identifiers and Peterson, J. and R. Barnes, "ACME Identifiers and
Challenges for Telephone Numbers", draft-ietf-acme- Challenges for Telephone Numbers", draft-ietf-acme-
telephone-01 (work in progress), October 2017. telephone-01 (work in progress), October 2017.
[I-D.vixie-dnsext-dns0x20] [I-D.vixie-dnsext-dns0x20]
Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to
Improve Transaction Identity", draft-vixie-dnsext- Improve Transaction Identity", draft-vixie-dnsext-
dns0x20-00 (work in progress), March 2008. dns0x20-00 (work in progress), March 2008.
 End of changes. 79 change blocks. 
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