draft-ietf-oauth-proof-of-possession-11.txt   rfc7800.txt 
OAuth Working Group M. Jones Internet Engineering Task Force (IETF) M. Jones
Internet-Draft Microsoft Request for Comments: 7800 Microsoft
Intended status: Standards Track J. Bradley Category: Standards Track J. Bradley
Expires: June 20, 2016 Ping Identity ISSN: 2070-1721 Ping Identity
H. Tschofenig H. Tschofenig
ARM Limited ARM Limited
December 18, 2015 April 2016
Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs) Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)
draft-ietf-oauth-proof-of-possession-11
Abstract Abstract
This specification defines how to declare in a JSON Web Token (JWT) This specification describes how to declare in a JSON Web Token (JWT)
that the presenter of the JWT possesses a particular proof-of- that the presenter of the JWT possesses a particular proof-of-
possession key and that the recipient can cryptographically confirm possession key and how the recipient can cryptographically confirm
proof-of-possession of the key by the presenter. Being able to prove proof of possession of the key by the presenter. Being able to prove
possession of a key is also sometimes described as the presenter possession of a key is also sometimes described as the presenter
being a holder-of-key. being a holder-of-key.
Status of this Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
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 This document is a product of the Internet Engineering Task Force
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time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
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Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on June 20, 2016. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7800.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 5 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Representations for Proof-of-Possession Keys . . . . . . . . . 6 3. Representations for Proof-of-Possession Keys . . . . . . . . 5
3.1. Confirmation Claim . . . . . . . . . . . . . . . . . . . . 6 3.1. Confirmation Claim . . . . . . . . . . . . . . . . . . . 6
3.2. Representation of an Asymmetric Proof-of-Possession Key . 7 3.2. Representation of an Asymmetric Proof-of-Possession Key . 7
3.3. Representation of an Encrypted Symmetric 3.3. Representation of an Encrypted Symmetric Proof-of-
Proof-of-Possession Key . . . . . . . . . . . . . . . . . 8 Possession Key . . . . . . . . . . . . . . . . . . . . . 7
3.4. Representation of a Key ID for a Proof-of-Possession 3.4. Representation of a Key ID for a Proof-of-Possession Key 8
Key . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.5. Representation of a URL for a Proof-of-Possession Key . . 9
3.5. Representation of a URL for a Proof-of-Possession Key . . 9 3.6. Specifics Intentionally Not Specified . . . . . . . . . . 10
3.6. Specifics Intentionally Not Specified . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6.1. JSON Web Token Claims Registration . . . . . . . . . . . 12
6.1. JSON Web Token Claims Registration . . . . . . . . . . . . 12 6.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 12
6.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 12 6.2. JWT Confirmation Methods Registry . . . . . . . . . . . . 12
6.2. JWT Confirmation Methods Registry . . . . . . . . . . . . 12 6.2.1. Registration Template . . . . . . . . . . . . . . . . 12
6.2.1. Registration Template . . . . . . . . . . . . . . . . 12 6.2.2. Initial Registry Contents . . . . . . . . . . . . . . 13
6.2.2. Initial Registry Contents . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 13 7.2. Informative References . . . . . . . . . . . . . . . . . 14
7.2. Informative References . . . . . . . . . . . . . . . . . . 14 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
Appendix B. Document History . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
This specification defines how a JSON Web Token [JWT] can declare This specification describes how a JSON Web Token [JWT] can declare
that the presenter of the JWT possesses a particular proof-of- that the presenter of the JWT possesses a particular proof-of-
possession (PoP) key and that the recipient can cryptographically possession (PoP) key and how the recipient can cryptographically
confirm proof-of-possession of the key by the presenter. Proof-of- confirm proof of possession of the key by the presenter. Proof of
possession of a key is also sometimes described as the presenter possession of a key is also sometimes described as the presenter
being a holder-of-key. The [I-D.ietf-oauth-pop-architecture] being a holder-of-key. The [OAUTH-POP-ARCH] specification describes
specification describes key confirmation, among other confirmation key confirmation, among other confirmation mechanisms. This
mechanisms. This specification defines how to communicate key specification defines how to communicate confirmation key information
confirmation key information in JWTs. in JWTs.
Envision the following two use cases. The first use case employs a Envision the following two use cases. The first use case employs a
symmetric proof-of-possession key and the second use case employs an symmetric proof-of-possession key and the second use case employs an
asymmetric proof-of-possession key. asymmetric proof-of-possession key.
+--------------+ +--------------+
| | +--------------+ | | +--------------+
| |--(3) Presentation of -->| | | |--(3) Presentation of -->| |
| | JWT w/ Encrypted | | | | JWT w/ Encrypted | |
| Presenter | PoP Key | | | Presenter | PoP Key | |
skipping to change at page 3, line 46 skipping to change at page 3, line 30
+--------------+ | | +--------------+ | |
| | | | | | | |
| | | | | | | |
| |<-(0) Key Exchange for ->| | | |<-(0) Key Exchange for ->| |
| Issuer | Key Encryption Key | | | Issuer | Key Encryption Key | |
| | | | | | | |
| | | | | | | |
| | +--------------+ | | +--------------+
+--------------+ +--------------+
Figure 1: Proof-of-Possession with a Symmetric Key Figure 1: Proof of Possession with a Symmetric Key
In the case illustrated in Figure 1, either the presenter generates a In the case illustrated in Figure 1, (1) either the presenter
symmetric key and privately sends it to the issuer (1) or the issuer generates a symmetric key and privately sends it to the issuer or the
generates a symmetric key and privately sends it to the presenter issuer generates a symmetric key and privately sends it to the
(1). The issuer generates a JWT with an encrypted copy of this presenter. The issuer generates a JWT with an encrypted copy of this
symmetric key in the confirmation claim. This symmetric key is symmetric key in the confirmation claim. This symmetric key is
encrypted with a key known only to the issuer and the recipient, encrypted with a key known only to the issuer and the recipient,
which was previously established in step (0). The entire JWT is which was previously established in step (0). The entire JWT is
integrity protected by the issuer. The JWT is then (2) sent to the integrity protected by the issuer. The JWT is then (2) sent to the
presenter. Now, the presenter is in possession of the symmetric key presenter. Now, the presenter is in possession of the symmetric key
as well as the JWT (which includes the confirmation claim). When the as well as the JWT (which includes the confirmation claim). When the
presenter (3) presents the JWT to the recipient, it also needs to presenter (3) presents the JWT to the recipient, it also needs to
demonstrate possession of the symmetric key; the presenter, for demonstrate possession of the symmetric key; the presenter, for
example, (4) uses the symmetric key in a challenge/response protocol example, (4) uses the symmetric key in a challenge/response protocol
with the recipient. The recipient is then able to verify that it is with the recipient. The recipient is then able to verify that it is
skipping to change at page 5, line 4 skipping to change at page 4, line 36
v | | | v | | |
+--------------+ | | +--------------+ | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| Issuer | | | | Issuer | | |
| | | | | | | |
| | | | | | | |
| | +--------------+ | | +--------------+
+--------------+ +--------------+
Figure 2: Proof-of-Possession with an Asymmetric Key
Figure 2: Proof of Possession with an Asymmetric Key
In the case illustrated in Figure 2, the presenter generates a In the case illustrated in Figure 2, the presenter generates a
public/private key pair and (1) sends the public key to the issuer, public/private key pair and (1) sends the public key to the issuer,
which creates a JWT that contains the public key (or an identifier which creates a JWT that contains the public key (or an identifier
for it) in the confirmation claim. The entire JWT is integrity for it) in the confirmation claim. The entire JWT is integrity
protected using a digital signature to protect it against protected using a digital signature to protect it against
modifications. The JWT is then (2) sent to the presenter. When the modifications. The JWT is then (2) sent to the presenter. When the
presenter (3) presents the JWT to the recipient, it also needs to presenter (3) presents the JWT to the recipient, it also needs to
demonstrate possession of the private key. The presenter, for demonstrate possession of the private key. The presenter, for
example, (4) uses the private key in a TLS exchange with the example, (4) uses the private key in a Transport Layer Security (TLS)
recipient or (4) signs a nonce with the private key. The recipient exchange with the recipient or (4) signs a nonce with the private
is able to verify that it is interacting with the genuine presenter key. The recipient is able to verify that it is interacting with the
by extracting the public key from the confirmation claim of the JWT genuine presenter by extracting the public key from the confirmation
(after verifying the digital signature of the JWT) and utilizing it claim of the JWT (after verifying the digital signature of the JWT)
with the private key in the TLS exchange or by checking the nonce and utilizing it with the private key in the TLS exchange or by
signature. checking the nonce signature.
In both cases, the JWT may contain other claims that are needed by In both cases, the JWT may contain other claims that are needed by
the application. the application.
1.1. Notational Conventions 1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
skipping to change at page 6, line 12 skipping to change at page 5, line 43
cryptography) or secret key (for symmetric key cryptography) to a cryptography) or secret key (for symmetric key cryptography) to a
recipient. recipient.
Recipient Recipient
Party that receives the JWT containing the proof-of-possession key Party that receives the JWT containing the proof-of-possession key
information from the presenter. information from the presenter.
3. Representations for Proof-of-Possession Keys 3. Representations for Proof-of-Possession Keys
By including a "cnf" (confirmation) claim in a JWT, the issuer of the By including a "cnf" (confirmation) claim in a JWT, the issuer of the
JWT declares that the presenter possesses a particular key, and that JWT declares that the presenter possesses a particular key and that
the recipient can cryptographically confirm that the presenter has the recipient can cryptographically confirm that the presenter has
possession of that key. The value of the "cnf" claim is a JSON possession of that key. The value of the "cnf" claim is a JSON
object and the members of that object identify the proof-of- object and the members of that object identify the proof-of-
possession key. possession key.
The presenter can be identified in one of several ways by the JWT, The presenter can be identified in one of several ways by the JWT
depending upon the application requirements. If the JWT contains a depending upon the application requirements. If the JWT contains a
"sub" (subject) claim [JWT], the presenter is normally the subject "sub" (subject) claim [JWT], the presenter is normally the subject
identified by the JWT. (In some applications, the subject identifier identified by the JWT. (In some applications, the subject identifier
will be relative to the issuer identified by the "iss" (issuer) claim will be relative to the issuer identified by the "iss" (issuer) claim
[JWT].) If the JWT contains no "sub" (subject) claim, the presenter [JWT].) If the JWT contains no "sub" claim, the presenter is
is normally the issuer identified by the JWT using the "iss" (issuer) normally the issuer identified by the JWT using the "iss" claim. The
claim. The case in which the presenter is the subject of the JWT is case in which the presenter is the subject of the JWT is analogous to
analogous to SAML 2.0 [OASIS.saml-core-2.0-os] SubjectConfirmation Security Assertion Markup Language (SAML) 2.0
usage. At least one of the "sub" and "iss" claims MUST be present in [OASIS.saml-core-2.0-os] SubjectConfirmation usage. At least one of
the JWT. Some use cases may require that both be present. the "sub" and "iss" claims MUST be present in the JWT. Some use
cases may require that both be present.
Another means used by some applications to identify the presenter is Another means used by some applications to identify the presenter is
an explicit claim, such as the "azp" (authorized party) claim defined an explicit claim, such as the "azp" (authorized party) claim defined
by OpenID Connect [OpenID.Core]. Ultimately, the means of by OpenID Connect [OpenID.Core]. Ultimately, the means of
identifying the presenter is application-specific, as is the means of identifying the presenter is application specific, as is the means of
confirming possession of the key that is communicated. confirming possession of the key that is communicated.
3.1. Confirmation Claim 3.1. Confirmation Claim
The "cnf" (confirmation) claim is used in the JWT to contain members The "cnf" claim is used in the JWT to contain members used to
used to identify the proof-of-possession key. Other members of the identify the proof-of-possession key. Other members of the "cnf"
"cnf" object may be defined because a proof-of-possession key may not object may be defined because a proof-of-possession key may not be
be the only means of confirming the authenticity of the token. This the only means of confirming the authenticity of the token. This is
is analogous to the SAML 2.0 [OASIS.saml-core-2.0-os] analogous to the SAML 2.0 [OASIS.saml-core-2.0-os]
SubjectConfirmation element, in which a number of different subject SubjectConfirmation element in which a number of different subject
confirmation methods can be included, including proof-of-possession confirmation methods can be included (including proof-of-possession
key information. key information).
The set of confirmation members that a JWT must contain to be The set of confirmation members that a JWT must contain to be
considered valid is context dependent and is outside the scope of considered valid is context dependent and is outside the scope of
this specification. Specific applications of JWTs will require this specification. Specific applications of JWTs will require
implementations to understand and process some confirmation members implementations to understand and process some confirmation members
in particular ways. However, in the absence of such requirements, in particular ways. However, in the absence of such requirements,
all confirmation members that are not understood by implementations all confirmation members that are not understood by implementations
MUST be ignored. MUST be ignored.
This specification establishes the IANA "JWT Confirmation Methods" This specification establishes the IANA "JWT Confirmation Methods"
registry for these members in Section 6.2 and registers the members registry for these members in Section 6.2 and registers the members
defined by this specification. Other specifications can register defined by this specification. Other specifications can register
other members used for confirmation, including other members for other members used for confirmation, including other members for
conveying proof-of-possession keys, possibly using different key conveying proof-of-possession keys using different key
representations. representations.
The "cnf" claim value MUST represent only a single proof-of- The "cnf" claim value MUST represent only a single proof-of-
possession key; thus, at most one of the "jwk", "jwe", and "jku" possession key; thus, at most one of the "jwk", "jwe", and "jku" (JWK
confirmation values defined below may be present. Note that if an Set URL) confirmation values defined below may be present. Note that
application needs to represent multiple proof-of-possession keys in if an application needs to represent multiple proof-of-possession
the same JWT, one way for it to achieve this is to use other claim keys in the same JWT, one way for it to achieve this is to use other
names, in addition to "cnf", to hold the additional proof-of- claim names, in addition to "cnf", to hold the additional proof-of-
possession key information. These claims could use the same syntax possession key information. These claims could use the same syntax
and semantics as the "cnf" claim. Those claims would be defined by and semantics as the "cnf" claim. Those claims would be defined by
applications or other specifications and could be registered in the applications or other specifications and could be registered in the
IANA "JSON Web Token Claims" registry [IANA.JWT.Claims]. IANA "JSON Web Token Claims" registry [IANA.JWT.Claims].
3.2. Representation of an Asymmetric Proof-of-Possession Key 3.2. Representation of an Asymmetric Proof-of-Possession Key
When the key held by the presenter is an asymmetric private key, the When the key held by the presenter is an asymmetric private key, the
"jwk" member is a JSON Web Key [JWK] representing the corresponding "jwk" member is a JSON Web Key [JWK] representing the corresponding
asymmetric public key. The following example demonstrates such a asymmetric public key. The following example demonstrates such a
skipping to change at page 7, line 48 skipping to change at page 7, line 32
"kty": "EC", "kty": "EC",
"use": "sig", "use": "sig",
"crv": "P-256", "crv": "P-256",
"x": "18wHLeIgW9wVN6VD1Txgpqy2LszYkMf6J8njVAibvhM", "x": "18wHLeIgW9wVN6VD1Txgpqy2LszYkMf6J8njVAibvhM",
"y": "-V4dS4UaLMgP_4fY4j8ir7cl1TXlFdAgcx55o7TkcSA" "y": "-V4dS4UaLMgP_4fY4j8ir7cl1TXlFdAgcx55o7TkcSA"
} }
} }
} }
The JWK MUST contain the required key members for a JWK of that key The JWK MUST contain the required key members for a JWK of that key
type and MAY contain other JWK members, including the "kid" (key ID) type and MAY contain other JWK members, including the "kid" (Key ID)
member. member.
The "jwk" member MAY also be used for a JWK representing a symmetric The "jwk" member MAY also be used for a JWK representing a symmetric
key, provided that the JWT is encrypted so that the key is not key, provided that the JWT is encrypted so that the key is not
revealed to unintended parties. If the JWT is not encrypted, the revealed to unintended parties. The means of encrypting a JWT is
symmetric key MUST be encrypted as described below. explained in [JWT]. If the JWT is not encrypted, the symmetric key
MUST be encrypted as described below.
3.3. Representation of an Encrypted Symmetric Proof-of-Possession Key 3.3. Representation of an Encrypted Symmetric Proof-of-Possession Key
When the key held by the presenter is a symmetric key, the "jwe" When the key held by the presenter is a symmetric key, the "jwe"
member is an encrypted JSON Web Key [JWK] encrypted to a key known to member is an encrypted JSON Web Key [JWK] encrypted to a key known to
the recipient using the JWE Compact Serialization containing the the recipient using the JWE Compact Serialization containing the
symmetric key. The rules for encrypting a JWK are found in Section 7 symmetric key. The rules for encrypting a JWK are found in Section 7
of the JSON Web Key [JWK] specification. of the JSON Web Key [JWK] specification.
The following example illustrates a symmetric key that could The following example illustrates a symmetric key that could
skipping to change at page 9, line 12 skipping to change at page 8, line 49
} }
} }
3.4. Representation of a Key ID for a Proof-of-Possession Key 3.4. Representation of a Key ID for a Proof-of-Possession Key
The proof-of-possession key can also be identified by the use of a The proof-of-possession key can also be identified by the use of a
Key ID instead of communicating the actual key, provided the Key ID instead of communicating the actual key, provided the
recipient is able to obtain the identified key using the Key ID. In recipient is able to obtain the identified key using the Key ID. In
this case, the issuer of a JWT declares that the presenter possesses this case, the issuer of a JWT declares that the presenter possesses
a particular key and that the recipient can cryptographically confirm a particular key and that the recipient can cryptographically confirm
proof-of-possession of the key by the presenter by including a "cnf" proof of possession of the key by the presenter by including a "cnf"
(confirmation) claim in the JWT whose value is a JSON object, with claim in the JWT whose value is a JSON object with the JSON object
the JSON object containing a "kid" (key ID) member identifying the containing a "kid" member identifying the key.
key.
The following example demonstrates such a declaration in the JWT The following example demonstrates such a declaration in the JWT
Claims Set of a JWT: Claims Set of a JWT:
{ {
"iss": "https://server.example.com", "iss": "https://server.example.com",
"aud": "https://client.example.org", "aud": "https://client.example.org",
"exp": 1361398824, "exp": 1361398824,
"cnf":{ "cnf":{
"kid": "dfd1aa97-6d8d-4575-a0fe-34b96de2bfad" "kid": "dfd1aa97-6d8d-4575-a0fe-34b96de2bfad"
} }
} }
The content of the "kid" value is application specific. For The content of the "kid" value is application specific. For
instance, some applications may choose to use a JWK Thumbprint instance, some applications may choose to use a JWK Thumbprint
[JWK.Thumbprint] value as the "kid" value. [JWK.Thumbprint] value as the "kid" value.
3.5. Representation of a URL for a Proof-of-Possession Key 3.5. Representation of a URL for a Proof-of-Possession Key
The proof-of-possession key can be passed by reference instead of The proof-of-possession key can be passed by reference instead of
being passed by value. This is done using the "jku" (JWK Set URL) being passed by value. This is done using the "jku" member. Its
member. Its value is a URI [RFC3986] that refers to a resource for a value is a URI [RFC3986] that refers to a resource for a set of JSON-
set of JSON-encoded public keys represented as a JWK Set [JWK], one encoded public keys represented as a JWK Set [JWK], one of which is
of which is the proof-of-possession key. If there are multiple keys the proof-of-possession key. If there are multiple keys in the
in the referenced JWK Set document, a "kid" member MUST also be referenced JWK Set document, a "kid" member MUST also be included
included, with the referenced key's JWK also containing the same with the referenced key's JWK also containing the same "kid" value.
"kid" value.
The protocol used to acquire the resource MUST provide integrity The protocol used to acquire the resource MUST provide integrity
protection. An HTTP GET request to retrieve the JWK Set MUST use protection. An HTTP GET request to retrieve the JWK Set MUST use TLS
Transport Layer Security (TLS) [RFC5246] and the identity of the [RFC5246] and the identity of the server MUST be validated, as per
server MUST be validated, as per Section 6 of RFC 6125 [RFC6125]. Section 6 of RFC 6125 [RFC6125].
The following example demonstrates such a declaration in the JWT The following example demonstrates such a declaration in the JWT
Claims Set of a JWT: Claims Set of a JWT:
{ {
"iss": "https://server.example.com", "iss": "https://server.example.com",
"sub": "17760704", "sub": "17760704",
"aud": "https://client.example.org", "aud": "https://client.example.org",
"exp": 1440804813, "exp": 1440804813,
"cnf":{ "cnf":{
"jku": "https://keys.example.net/pop-keys.json", "jku": "https://keys.example.net/pop-keys.json",
"kid": "2015-08-28" "kid": "2015-08-28"
} }
} }
3.6. Specifics Intentionally Not Specified 3.6. Specifics Intentionally Not Specified
Proof-of-possession is typically demonstrated by having the presenter Proof of possession is typically demonstrated by having the presenter
sign a value determined by the recipient using the key possessed by sign a value determined by the recipient using the key possessed by
the presenter. This value is sometimes called a "nonce" or a the presenter. This value is sometimes called a "nonce" or a
"challenge". "challenge".
The means of communicating the nonce and the nature of its contents The means of communicating the nonce and the nature of its contents
are intentionally not described in this specification, as different are intentionally not described in this specification, as different
protocols will communicate this information in different ways. protocols will communicate this information in different ways.
Likewise, the means of communicating the signed nonce is also not Likewise, the means of communicating the signed nonce is also not
specified, as this is also protocol-specific. specified, as this is also protocol specific.
Note that another means of proving possession of the key when it is a Note that another means of proving possession of the key when it is a
symmetric key is to encrypt the key to the recipient. The means of symmetric key is to encrypt the key to the recipient. The means of
obtaining a key for the recipient is likewise protocol-specific. obtaining a key for the recipient is likewise protocol specific.
For examples using the mechanisms defined in this specification, see For examples using the mechanisms defined in this specification, see
[I-D.ietf-oauth-pop-architecture]. [OAUTH-POP-ARCH].
4. Security Considerations 4. Security Considerations
All of the security considerations that are discussed in [JWT] also All of the security considerations that are discussed in [JWT] also
apply here. In addition, proof-of-possession introduces its own apply here. In addition, proof of possession introduces its own
unique security issues. Possessing a key is only valuable if it is unique security issues. Possessing a key is only valuable if it is
kept secret. Appropriate means must be used to ensure that kept secret. Appropriate means must be used to ensure that
unintended parties do not learn private key or symmetric key values. unintended parties do not learn private key or symmetric key values.
Applications utilizing proof-of-possession should also utilize Applications utilizing proof of possession should also utilize
audience restriction, as described in Section 4.1.3 of [JWT], as it audience restriction, as described in Section 4.1.3 of [JWT], as it
provides different protections. Proof-of-possession can be used by provides different protections. Proof of possession can be used by
recipients to reject messages from unauthorized senders. Audience recipients to reject messages from unauthorized senders. Audience
restriction can be used by recipients to reject messages intended for restriction can be used by recipients to reject messages intended for
different recipients. different recipients.
A recipient might not understand the "cnf" claim. Applications that A recipient might not understand the "cnf" claim. Applications that
require the proof-of-possession keys communicated with it to be require the proof-of-possession keys communicated with it to be
understood and processed must ensure that the parts of this understood and processed must ensure that the parts of this
specification that they use are implemented. specification that they use are implemented.
Proof-of-possession via encrypted symmetric secrets is subject to Proof of possession via encrypted symmetric secrets is subject to
replay attacks. This attack can be avoided when a signed nonce or replay attacks. This attack can, for example, be avoided when a
challenge is used, since the recipient can use a distinct nonce or signed nonce or challenge is used since the recipient can use a
challenge for each interaction. Replay can also be avoided if a sub- distinct nonce or challenge for each interaction. Replay can also be
key is derived from a shared secret that is specific to the instance avoided if a sub-key is derived from a shared secret that is specific
of the PoP demonstration. to the instance of the PoP demonstration.
Similarly to other information included in a JWT, it is necessary to As is the case with other information included in a JWT, it is
apply data origin authentication and integrity protection (via a necessary to apply data origin authentication and integrity
keyed message digest or a digital signature). Data origin protection (via a keyed message digest or a digital signature). Data
authentication ensures that the recipient of the JWT learns about the origin authentication ensures that the recipient of the JWT learns
entity that created the JWT, since this will be important for any about the entity that created the JWT since this will be important
policy decisions. Integrity protection prevents an adversary from for any policy decisions. Integrity protection prevents an adversary
changing any elements conveyed within the JWT payload. Special care from changing any elements conveyed within the JWT payload. Special
has to be applied when carrying symmetric keys inside the JWT, since care has to be applied when carrying symmetric keys inside the JWT
those not only require integrity protection, but also confidentiality since those not only require integrity protection but also
protection. confidentiality protection.
5. Privacy Considerations 5. Privacy Considerations
A proof-of-possession key can be used as a correlation handle if the A proof-of-possession key can be used as a correlation handle if the
same key is used with multiple parties. Thus, for privacy reasons, same key is used with multiple parties. Thus, for privacy reasons,
it is recommended that different proof-of-possession keys be used it is recommended that different proof-of-possession keys be used
when interacting with different parties. when interacting with different parties.
6. IANA Considerations 6. IANA Considerations
The following registration procedure is used for all the registries The following registration procedure is used for all the registries
established by this specification. established by this specification.
Values are registered on a Specification Required [RFC5226] basis Values are registered on a Specification Required [RFC5226] basis
after a three-week review period on the oauth-pop-reg-review@ietf.org after a three-week review period on the jwt-reg-review@ietf.org
mailing list, on the advice of one or more Designated Experts. mailing list, on the advice of one or more Designated Experts.
However, to allow for the allocation of values prior to publication, However, to allow for the allocation of values prior to publication,
the Designated Experts may approve registration once they are the Designated Experts may approve registration once they are
satisfied that such a specification will be published. [[ Note to the satisfied that such a specification will be published.
RFC Editor: The name of the mailing list should be determined in
consultation with the IESG and IANA. Suggested name:
oauth-pop-reg-review@ietf.org. ]]
Registration requests sent to the mailing list for review should use Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register JWT Confirmation an appropriate subject (e.g., "Request to Register JWT Confirmation
Method: example"). Registration requests that are undetermined for a Method: example"). Registration requests that are undetermined for a
period longer than 21 days can be brought to the IESG's attention period longer than 21 days can be brought to the IESG's attention
(using the iesg@ietf.org mailing list) for resolution. (using the iesg@ietf.org mailing list) for resolution.
Criteria that should be applied by the Designated Experts include Criteria that should be applied by the Designated Experts include
determining whether the proposed registration duplicates existing determining whether the proposed registration duplicates existing
functionality, determining whether it is likely to be of general functionality, determining whether it is likely to be of general
applicability or whether it is useful only for a single application, applicability or whether it is useful only for a single application,
evaluating the security properties of the item being registered, and and evaluating the security properties of the item being registered
whether the registration makes sense. and whether the registration makes sense.
It is suggested that multiple Designated Experts be appointed who are It is suggested that multiple Designated Experts be appointed who are
able to represent the perspectives of different applications using able to represent the perspectives of different applications using
this specification, in order to enable broadly-informed review of this specification in order to enable broadly informed review of
registration decisions. In cases where a registration decision could registration decisions. In cases where a registration decision could
be perceived as creating a conflict of interest for a particular be perceived as creating a conflict of interest for a particular
Expert, that Expert should defer to the judgment of the other Expert, that Expert should defer to the judgment of the other
Experts. Experts.
6.1. JSON Web Token Claims Registration 6.1. JSON Web Token Claims Registration
This specification registers the "cnf" claim in the IANA "JSON Web This specification registers the "cnf" claim in the IANA "JSON Web
Token Claims" registry [IANA.JWT.Claims] established by [JWT]. Token Claims" registry [IANA.JWT.Claims] established by [JWT].
6.1.1. Registry Contents 6.1.1. Registry Contents
o Claim Name: "cnf" o Claim Name: "cnf"
o Claim Description: Confirmation o Claim Description: Confirmation
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.1 of [[ this document ]] o Specification Document(s): Section 3.1 of [RFC7800]
6.2. JWT Confirmation Methods Registry 6.2. JWT Confirmation Methods Registry
This specification establishes the IANA "JWT Confirmation Methods" This specification establishes the IANA "JWT Confirmation Methods"
registry for JWT "cnf" member values. The registry records the registry for JWT "cnf" member values. The registry records the
confirmation method member and a reference to the specification that confirmation method member and a reference to the specification that
defines it. defines it.
6.2.1. Registration Template 6.2.1. Registration Template
Confirmation Method Value: Confirmation Method Value:
The name requested (e.g., "kid"). Because a core goal of this The name requested (e.g., "kid"). Because a core goal of this
specification is for the resulting representations to be compact, specification is for the resulting representations to be compact,
it is RECOMMENDED that the name be short -- not to exceed 8 it is RECOMMENDED that the name be short -- not to exceed eight
characters without a compelling reason to do so. This name is characters without a compelling reason to do so. This name is
case-sensitive. Names may not match other registered names in a case sensitive. Names may not match other registered names in a
case-insensitive manner unless the Designated Experts state that case-insensitive manner unless the Designated Experts state that
there is a compelling reason to allow an exception. there is a compelling reason to allow an exception.
Confirmation Method Description: Confirmation Method Description:
Brief description of the confirmation method (e.g., "Key Brief description of the confirmation method (e.g., "Key
Identifier"). Identifier").
Change Controller: Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal name of the responsible party. Other details (e.g., postal
skipping to change at page 13, line 26 skipping to change at page 13, line 11
preferably including URIs that can be used to retrieve copies of preferably including URIs that can be used to retrieve copies of
the documents. An indication of the relevant sections may also be the documents. An indication of the relevant sections may also be
included but is not required. included but is not required.
6.2.2. Initial Registry Contents 6.2.2. Initial Registry Contents
o Confirmation Method Value: "jwk" o Confirmation Method Value: "jwk"
o Confirmation Method Description: JSON Web Key Representing Public o Confirmation Method Description: JSON Web Key Representing Public
Key Key
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.2 of [[ this document ]] o Specification Document(s): Section 3.2 of [RFC7800]
o Confirmation Method Value: "jwe" o Confirmation Method Value: "jwe"
o Confirmation Method Description: Encrypted JSON Web Key o Confirmation Method Description: Encrypted JSON Web Key
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.3 of [[ this document ]] o Specification Document(s): Section 3.3 of [RFC7800]
o Confirmation Method Value: "kid" o Confirmation Method Value: "kid"
o Confirmation Method Description: Key Identifier o Confirmation Method Description: Key Identifier
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.4 of [[ this document ]] o Specification Document(s): Section 3.4 of [RFC7800]
o Confirmation Method Value: "jku" o Confirmation Method Value: "jku"
o Confirmation Method Description: JWK Set URL o Confirmation Method Description: JWK Set URL
o Change Controller: IESG o Change Controller: IESG
o Specification Document(s): Section 3.5 of [[ this document ]] o Specification Document(s): Section 3.5 of [RFC7800]
7. References 7. References
7.1. Normative References 7.1. Normative References
[IANA.JWT.Claims] [IANA.JWT.Claims]
IANA, "JSON Web Token Claims", IANA, "JSON Web Token Claims",
<http://www.iana.org/assignments/jwt>. <http://www.iana.org/assignments/jwt>.
[JWE] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", [JWE] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7156, May 2015, RFC 7516, DOI 10.17487/RFC7156, May 2015,
<http://www.rfc-editor.org/info/rfc7516>. <http://www.rfc-editor.org/info/rfc7516>.
[JWK] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/ [JWK] Jones, M., "JSON Web Key (JWK)", RFC 7517,
RFC7157, May 2015, DOI 10.17487/RFC7157, May 2015,
<http://www.rfc-editor.org/info/rfc7517>. <http://www.rfc-editor.org/info/rfc7517>.
[JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token [JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7159, May 2015, (JWT)", RFC 7519, DOI 10.17487/RFC7159, May 2015,
<http://www.rfc-editor.org/info/rfc7519>. <http://www.rfc-editor.org/info/rfc7519>.
[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, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
November 2003, <http://www.rfc-editor.org/info/rfc3629>. 2003, <http://www.rfc-editor.org/info/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>. <http://www.rfc-editor.org/info/rfc3986>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008, DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>. <http://www.rfc-editor.org/info/rfc5226>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ (TLS) Protocol Version 1.2", RFC 5246,
RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://www.rfc-editor.org/info/rfc5246>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
March 2011, <http://www.rfc-editor.org/info/rfc6125>. 2011, <http://www.rfc-editor.org/info/rfc6125>.
7.2. Informative References 7.2. Informative References
[I-D.ietf-oauth-pop-architecture]
Hunt, P., Richer, J., Mills, W., Mishra, P., and H.
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
Architecture", draft-ietf-oauth-pop-architecture-05 (work
in progress), October 2015.
[JWK.Thumbprint] [JWK.Thumbprint]
Jones, M. and N. Sakimura, "JSON Web Key (JWK) Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
September 2015, <http://www.rfc-editor.org/info/rfc7638>. 2015, <http://www.rfc-editor.org/info/rfc7638>.
[OASIS.saml-core-2.0-os] [OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler, Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion "Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core- Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005. 2.0-os, March 2005,
<http://docs.oasis-open.org/security/saml/v2.0/>.
[OAUTH-POP-ARCH]
Hunt, P., Ed, Richer, J., Mills, W., Mishra, P., and H.
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
Architecture", Work in Progress, draft-ietf-oauth-pop-
architecture-07, December 2015.
[OpenID.Core] [OpenID.Core]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", November 2014, C. Mortimore, "OpenID Connect Core 1.0", November 2014,
<http://openid.net/specs/openid-connect-core-1_0.html>. <http://openid.net/specs/openid-connect-core-1_0.html>.
Appendix A. Acknowledgements Acknowledgements
The authors wish to thank Brian Campbell, Stephen Farrell, Barry The authors wish to thank Brian Campbell, Stephen Farrell, Barry
Leiba, Kepeng Li, Chris Lonvick, James Manger, Kathleen Moriarty, Leiba, Kepeng Li, Chris Lonvick, James Manger, Kathleen Moriarty,
Justin Richer, and Nat Sakimura for their reviews of the Justin Richer, and Nat Sakimura for their reviews of the
specification. specification.
Appendix B. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-11
o Addressed Sec-Dir review comments by Chris Lonvick and ballot
comments by Stephen Farrell.
-10
o Addressed ballot comments by Barry Leiba.
-09
o Removed erroneous quotation marks around numeric "exp" claim
values in examples.
-08
o Added security consideration about also utilizing audience
restriction.
-07
o Addressed review comments by Hannes Tschofenig, Kathleen Moriarty,
and Justin Richer. Changes were:
o Clarified that symmetric proof-of-possession keys can be generated
by either the presenter or the issuer.
o Clarified that confirmation members that are not understood must
be ignored unless otherwise specified by the application.
-06
o Added diagrams to the introduction.
-05
o Addressed review comments by Kepeng Li.
-04
o Allowed the use of "jwk" for symmetric keys when the JWT is
encrypted.
o Added the "jku" (JWK Set URL) member.
o Added privacy considerations.
o Reordered sections so that the "cnf" (confirmation) claim is
defined before it is used.
o Noted that applications can define new claim names, in addition to
"cnf", to represent additional proof-of-possession keys, using the
same representation as "cnf".
o Applied wording clarifications suggested by Nat Sakimura.
-03
o Separated the "jwk" and "jwe" confirmation members; the former
represents a public key as a JWK and the latter represents a
symmetric key as a JWE encrypted JWK.
o Changed the title to indicate that a proof-of-possession key is
being communicated.
o Updated language that formerly assumed that the issuer was an
OAuth 2.0 authorization server.
o Described ways that applications can choose to identify the
presenter, including use of the "iss", "sub", and "azp" claims.
o Harmonized the registry language with that used in JWT [RFC 7519].
o Addressed other issues identified during working group last call.
o Referenced the JWT and JOSE RFCs.
-02
o Defined the terms Issuer, Presenter, and Recipient and updated
their usage within the document.
o Added a description of a use case using an asymmetric proof-of-
possession key to the introduction.
o Added the "kid" (key ID) confirmation method.
o These changes address the open issues identified in the previous
draft.
-01
o Updated references.
-00
o Created the initial working group draft from
draft-jones-oauth-proof-of-possession-02.
Authors' Addresses Authors' Addresses
Michael B. Jones Michael B. Jones
Microsoft Microsoft
Email: mbj@microsoft.com Email: mbj@microsoft.com
URI: http://self-issued.info/ URI: http://self-issued.info/
John Bradley John Bradley
Ping Identity Ping Identity
Email: ve7jtb@ve7jtb.com Email: ve7jtb@ve7jtb.com
URI: http://www.thread-safe.com/ URI: http://www.thread-safe.com/
Hannes Tschofenig Hannes Tschofenig
ARM Limited ARM Limited
Austria Austria
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