draft-ietf-oauth-jwt-bcp-07.txt   rfc8725.txt 
OAuth Working Group Y. Sheffer Internet Engineering Task Force (IETF) Y. Sheffer
Internet-Draft Intuit Request for Comments: 8725 Intuit
Updates: RFC 7519 (if approved) D. Hardt BCP: 225 D. Hardt
Intended status: Best Current Practice Updates: 7519
Expires: April 15, 2020 M. Jones Category: Best Current Practice M. Jones
Microsoft ISSN: 2070-1721 Microsoft
October 13, 2019 February 2020
JSON Web Token Best Current Practices JSON Web Token Best Current Practices
draft-ietf-oauth-jwt-bcp-07
Abstract Abstract
JSON Web Tokens, also known as JWTs, are URL-safe JSON-based security JSON Web Tokens, also known as JWTs, are URL-safe JSON-based security
tokens that contain a set of claims that can be signed and/or tokens that contain a set of claims that can be signed and/or
encrypted. JWTs are being widely used and deployed as a simple encrypted. JWTs are being widely used and deployed as a simple
security token format in numerous protocols and applications, both in security token format in numerous protocols and applications, both in
the area of digital identity, and in other application areas. The the area of digital identity and in other application areas. This
goal of this Best Current Practices document is to provide actionable Best Current Practices document updates RFC 7519 to provide
guidance leading to secure implementation and deployment of JWTs. actionable guidance leading to secure implementation and deployment
of JWTs.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This memo documents an Internet Best Current Practice.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 7841.
This Internet-Draft will expire on April 15, 2020. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8725.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. Target Audience . . . . . . . . . . . . . . . . . . . . . 4 1.1. Target Audience
1.2. Conventions used in this document . . . . . . . . . . . . 4 1.2. Conventions Used in this Document
2. Threats and Vulnerabilities . . . . . . . . . . . . . . . . . 4 2. Threats and Vulnerabilities
2.1. Weak Signatures and Insufficient Signature Validation . . 4 2.1. Weak Signatures and Insufficient Signature Validation
2.2. Weak Symmetric Keys . . . . . . . . . . . . . . . . . . . 5 2.2. Weak Symmetric Keys
2.3. Incorrect Composition of Encryption and Signature . . . . 5 2.3. Incorrect Composition of Encryption and Signature
2.4. Plaintext Leakage through Analysis of Ciphertext Length . 5 2.4. Plaintext Leakage through Analysis of Ciphertext Length
2.5. Insecure Use of Elliptic Curve Encryption . . . . . . . . 5 2.5. Insecure Use of Elliptic Curve Encryption
2.6. Multiplicity of JSON Encodings . . . . . . . . . . . . . 6 2.6. Multiplicity of JSON Encodings
2.7. Substitution Attacks . . . . . . . . . . . . . . . . . . 6 2.7. Substitution Attacks
2.8. Cross-JWT Confusion . . . . . . . . . . . . . . . . . . . 6 2.8. Cross-JWT Confusion
2.9. Indirect Attacks on the Server . . . . . . . . . . . . . 6 2.9. Indirect Attacks on the Server
3. Best Practices . . . . . . . . . . . . . . . . . . . . . . . 7 3. Best Practices
3.1. Perform Algorithm Verification . . . . . . . . . . . . . 7 3.1. Perform Algorithm Verification
3.2. Use Appropriate Algorithms . . . . . . . . . . . . . . . 7 3.2. Use Appropriate Algorithms
3.3. Validate All Cryptographic Operations . . . . . . . . . . 8 3.3. Validate All Cryptographic Operations
3.4. Validate Cryptographic Inputs . . . . . . . . . . . . . . 8 3.4. Validate Cryptographic Inputs
3.5. Ensure Cryptographic Keys have Sufficient Entropy . . . . 8 3.5. Ensure Cryptographic Keys Have Sufficient Entropy
3.6. Avoid Length-Dependent Encryption Inputs . . . . . . . . 9 3.6. Avoid Compression of Encryption Inputs
3.7. Use UTF-8 . . . . . . . . . . . . . . . . . . . . . . . . 9 3.7. Use UTF-8
3.8. Validate Issuer and Subject . . . . . . . . . . . . . . . 9 3.8. Validate Issuer and Subject
3.9. Use and Validate Audience . . . . . . . . . . . . . . . . 9 3.9. Use and Validate Audience
3.10. Do Not Trust Received Claims . . . . . . . . . . . . . . 10 3.10. Do Not Trust Received Claims
3.11. Use Explicit Typing . . . . . . . . . . . . . . . . . . . 10 3.11. Use Explicit Typing
3.12. Use Mutually Exclusive Validation Rules for Different 3.12. Use Mutually Exclusive Validation Rules for Different Kinds
Kinds of JWTs . . . . . . . . . . . . . . . . . . . . . . 11 of JWTs
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11 4. Security Considerations
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 5. IANA Considerations
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 6. References
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative References
7.1. Normative References . . . . . . . . . . . . . . . . . . 12 6.2. Informative References
7.2. Informative References . . . . . . . . . . . . . . . . . 13 Acknowledgements
Appendix A. Document History . . . . . . . . . . . . . . . . . . 15 Authors' Addresses
A.1. draft-ietf-oauth-jwt-bcp-07 . . . . . . . . . . . . . . . 15
A.2. draft-ietf-oauth-jwt-bcp-06 . . . . . . . . . . . . . . . 15
A.3. draft-ietf-oauth-jwt-bcp-05 . . . . . . . . . . . . . . . 15
A.4. draft-ietf-oauth-jwt-bcp-04 . . . . . . . . . . . . . . . 15
A.5. draft-ietf-oauth-jwt-bcp-03 . . . . . . . . . . . . . . . 15
A.6. draft-ietf-oauth-jwt-bcp-02 . . . . . . . . . . . . . . . 15
A.7. draft-ietf-oauth-jwt-bcp-01 . . . . . . . . . . . . . . . 15
A.8. draft-ietf-oauth-jwt-bcp-00 . . . . . . . . . . . . . . . 15
A.9. draft-sheffer-oauth-jwt-bcp-01 . . . . . . . . . . . . . 15
A.10. draft-sheffer-oauth-jwt-bcp-00 . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
JSON Web Tokens, also known as JWTs [RFC7519], are URL-safe JSON- JSON Web Tokens, also known as JWTs [RFC7519], are URL-safe JSON-
based security tokens that contain a set of claims that can be signed based security tokens that contain a set of claims that can be signed
and/or encrypted. The JWT specification has seen rapid adoption and/or encrypted. The JWT specification has seen rapid adoption
because it encapsulates security-relevant information in one easy-to- because it encapsulates security-relevant information in one easy-to-
protect location, and because it is easy to implement using widely- protect location, and because it is easy to implement using widely
available tools. One application area in which JWTs are commonly available tools. One application area in which JWTs are commonly
used is representing digital identity information, such as OpenID used is representing digital identity information, such as OpenID
Connect ID Tokens [OpenID.Core] and OAuth 2.0 [RFC6749] access tokens Connect ID Tokens [OpenID.Core] and OAuth 2.0 [RFC6749] access tokens
and refresh tokens, the details of which are deployment-specific. and refresh tokens, the details of which are deployment-specific.
Since the JWT specification was published, there have been several Since the JWT specification was published, there have been several
widely published attacks on implementations and deployments. Such widely published attacks on implementations and deployments. Such
attacks are the result of under-specified security mechanisms, as attacks are the result of under-specified security mechanisms, as
well as incomplete implementations and incorrect usage by well as incomplete implementations and incorrect usage by
applications. applications.
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importance of cryptographic strength vs. computational load). importance of cryptographic strength vs. computational load).
Community knowledge about the strength of various algorithms and Community knowledge about the strength of various algorithms and
feasible attacks can change quickly, and experience shows that a Best feasible attacks can change quickly, and experience shows that a Best
Current Practice (BCP) document about security is a point-in-time Current Practice (BCP) document about security is a point-in-time
statement. Readers are advised to seek out any errata or updates statement. Readers are advised to seek out any errata or updates
that apply to this document. that apply to this document.
1.1. Target Audience 1.1. Target Audience
The intended audience of this document is: The intended audiences of this document are:
- Implementers of JWT libraries (and the JWS and JWE libraries used * Implementers of JWT libraries (and the JWS and JWE libraries used
by those libraries), by those libraries),
- Implementers of code that uses such libraries (to the extent that * Implementers of code that uses such libraries (to the extent that
some mechanisms may not be provided by libraries, or until they some mechanisms may not be provided by libraries, or until they
are), and are), and
- Developers of specifications that rely on JWTs, both inside and * Developers of specifications that rely on JWTs, both inside and
outside the IETF. outside the IETF.
1.2. Conventions used in this document 1.2. Conventions Used in this Document
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 "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Threats and Vulnerabilities 2. Threats and Vulnerabilities
This section lists some known and possible problems with JWT This section lists some known and possible problems with JWT
implementations and deployments. Each problem description is implementations and deployments. Each problem description is
followed by references to one or more mitigations to those problems. followed by references to one or more mitigations to those problems.
2.1. Weak Signatures and Insufficient Signature Validation 2.1. Weak Signatures and Insufficient Signature Validation
Signed JSON Web Tokens carry an explicit indication of the signing Signed JSON Web Tokens carry an explicit indication of the signing
algorithm, in the form of the "alg" header parameter, to facilitate algorithm, in the form of the "alg" Header Parameter, to facilitate
cryptographic agility. This, in conjunction with design flaws in cryptographic agility. This, in conjunction with design flaws in
some libraries and applications, have led to several attacks: some libraries and applications, has led to several attacks:
- The algorithm can be changed to "none" by an attacker, and some * The algorithm can be changed to "none" by an attacker, and some
libraries would trust this value and "validate" the JWT without libraries would trust this value and "validate" the JWT without
checking any signature. checking any signature.
- An "RS256" (RSA, 2048 bit) parameter value can be changed into * An "RS256" (RSA, 2048 bit) parameter value can be changed into
"HS256" (HMAC, SHA-256), and some libraries would try to validate "HS256" (HMAC, SHA-256), and some libraries would try to validate
the signature using HMAC-SHA256 and using the RSA public key as the signature using HMAC-SHA256 and using the RSA public key as
the HMAC shared secret (see [McLean] and CVE-2015-9235). the HMAC shared secret (see [McLean] and [CVE-2015-9235]).
For mitigations, see Section 3.1 and Section 3.2. For mitigations, see Sections 3.1 and 3.2.
2.2. Weak Symmetric Keys 2.2. Weak Symmetric Keys
In addition, some applications use a keyed MAC algorithm such as In addition, some applications use a keyed Message Authentication
"HS256" to sign tokens, but supply a weak symmetric key with Code (MAC) algorithm, such as "HS256", to sign tokens but supply a
insufficient entropy (such as a human memorable password). Such keys weak symmetric key with insufficient entropy (such as a human-
are vulnerable to offline brute-force or dictionary attacks once an memorable password). Such keys are vulnerable to offline brute-force
attacker gets hold of such a token [Langkemper]. or dictionary attacks once an attacker gets hold of such a token
[Langkemper].
For mitigations, see Section 3.5. For mitigations, see Section 3.5.
2.3. Incorrect Composition of Encryption and Signature 2.3. Incorrect Composition of Encryption and Signature
Some libraries that decrypt a JWE-encrypted JWT to obtain a JWS- Some libraries that decrypt a JWE-encrypted JWT to obtain a JWS-
signed object do not always validate the internal signature. signed object do not always validate the internal signature.
For mitigations, see Section 3.3. For mitigations, see Section 3.3.
2.4. Plaintext Leakage through Analysis of Ciphertext Length 2.4. Plaintext Leakage through Analysis of Ciphertext Length
Many encryption algorithms leak information about the length of the Many encryption algorithms leak information about the length of the
plaintext, with a varying amount of leakage depending on the plaintext, with a varying amount of leakage depending on the
algorithm and mode of operation. This problem is exacerbated when algorithm and mode of operation. This problem is exacerbated when
the plaintext is initially compressed, because the length of the the plaintext is initially compressed, because the length of the
compressed plaintext and, thus, the ciphertext depend not only on the compressed plaintext and, thus, the ciphertext depends not only on
length of the original plaintext but also on its content. the length of the original plaintext but also on its content.
Compression attacks are particularly powerful when there is attacker- Compression attacks are particularly powerful when there is attacker-
controlled data in the same compression space as secret data, as is controlled data in the same compression space as secret data, which
the case for some attacks on HTTPS. is the case for some attacks on HTTPS.
See [Kelsey] for general background on compression and encryption, See [Kelsey] for general background on compression and encryption and
and [Alawatugoda] for a specific example of attacks on HTTP cookies. [Alawatugoda] for a specific example of attacks on HTTP cookies.
For mitigations, see Section 3.6. For mitigations, see Section 3.6.
2.5. Insecure Use of Elliptic Curve Encryption 2.5. Insecure Use of Elliptic Curve Encryption
Per [Sanso], several JOSE libraries fail to validate their inputs Per [Sanso], several Javascript Object Signing and Encryption (JOSE)
correctly when performing elliptic curve key agreement (the "ECDH-ES" libraries fail to validate their inputs correctly when performing
algorithm). An attacker that is able to send JWEs of its choosing elliptic curve key agreement (the "ECDH-ES" algorithm). An attacker
that use invalid curve points and observe the cleartext outputs that is able to send JWEs of its choosing that use invalid curve
resulting from decryption with the invalid curve points can use this points and observe the cleartext outputs resulting from decryption
vulnerability to recover the recipient's private key. with the invalid curve points can use this vulnerability to recover
the recipient's private key.
For mitigations, see Section 3.4. For mitigations, see Section 3.4.
2.6. Multiplicity of JSON Encodings 2.6. Multiplicity of JSON Encodings
Previous versions of the JSON format such as the obsoleted [RFC7159] Previous versions of the JSON format, such as the obsoleted
allowed several different character encodings: UTF-8, UTF-16 and UTF- [RFC7159], allowed several different character encodings: UTF-8, UTF-
32. This is not the case anymore, with the latest standard [RFC8259] 16, and UTF-32. This is not the case anymore, with the latest
only allowing UTF-8 except for internal use within a "closed standard [RFC8259] only allowing UTF-8 except for internal use within
ecosystem". This ambiguity where older implementations and those a "closed ecosystem". This ambiguity, where older implementations
used within closed environments may generate non-standard encodings, and those used within closed environments may generate non-standard
may result in the JWT being misinterpreted by its recipient. This in encodings, may result in the JWT being misinterpreted by its
turn could be used by a malicious sender to bypass the recipient's recipient. This, in turn, could be used by a malicious sender to
validation checks. bypass the recipient's validation checks.
For mitigations, see Section 3.7. For mitigations, see Section 3.7.
2.7. Substitution Attacks 2.7. Substitution Attacks
There are attacks in which one recipient will be given a JWT that was There are attacks in which one recipient will be given a JWT that was
intended for it, and will attempt to use it at a different recipient intended for it and will attempt to use it at a different recipient
for which that JWT was not intended. For instance, if an OAuth 2.0 for which that JWT was not intended. For instance, if an OAuth 2.0
[RFC6749] access token is legitimately presented to an OAuth 2.0 [RFC6749] access token is legitimately presented to an OAuth 2.0
protected resource for which it is intended, that protected resource protected resource for which it is intended, that protected resource
might then present that same access token to a different protected might then present that same access token to a different protected
resource for which the access token is not intended, in an attempt to resource for which the access token is not intended, in an attempt to
gain access. If such situations are not caught, this can result in gain access. If such situations are not caught, this can result in
the attacker gaining access to resources that it is not entitled to the attacker gaining access to resources that it is not entitled to
access. access.
For mitigations, see Section 3.8 and Section 3.9. For mitigations, see Sections 3.8 and 3.9.
2.8. Cross-JWT Confusion 2.8. Cross-JWT Confusion
As JWTs are being used by more different protocols in diverse As JWTs are being used by more different protocols in diverse
application areas, it becomes increasingly important to prevent cases application areas, it becomes increasingly important to prevent cases
of JWT tokens that have been issued for one purpose being subverted of JWT tokens that have been issued for one purpose being subverted
and used for another. Note that this is a specific type of and used for another. Note that this is a specific type of
substitution attack. If the JWT could be used in an application substitution attack. If the JWT could be used in an application
context in which it could be confused with other kinds of JWTs, then context in which it could be confused with other kinds of JWTs, then
mitigations MUST be employed to prevent these substitution attacks. mitigations MUST be employed to prevent these substitution attacks.
For mitigations, see Section 3.8, Section 3.9, Section 3.11, and For mitigations, see Sections 3.8, 3.9, 3.11, and 3.12.
Section 3.12.
2.9. Indirect Attacks on the Server 2.9. Indirect Attacks on the Server
Various JWT claims are used by the recipient to perform lookup Various JWT claims are used by the recipient to perform lookup
operations, such as database and LDAP searches. Others include URLs operations, such as database and Lightweight Directory Access
that are similarly looked up by the server. Any of these claims can Protocol (LDAP) searches. Others include URLs that are similarly
be used by an attacker as vectors for injection attacks or server- looked up by the server. Any of these claims can be used by an
side request forgery (SSRF) attacks. attacker as vectors for injection attacks or server-side request
forgery (SSRF) attacks.
For mitigations, see Section 3.10. For mitigations, see Section 3.10.
3. Best Practices 3. Best Practices
The best practices listed below should be applied by practitioners to The best practices listed below should be applied by practitioners to
mitigate the threats listed in the preceding section. mitigate the threats listed in the preceding section.
3.1. Perform Algorithm Verification 3.1. Perform Algorithm Verification
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cryptographic weaknesses. Applications MUST therefore be designed to cryptographic weaknesses. Applications MUST therefore be designed to
enable cryptographic agility. enable cryptographic agility.
That said, if a JWT is cryptographically protected end-to-end by a That said, if a JWT is cryptographically protected end-to-end by a
transport layer, such as TLS using cryptographically current transport layer, such as TLS using cryptographically current
algorithms, there may be no need to apply another layer of algorithms, there may be no need to apply another layer of
cryptographic protections to the JWT. In such cases, the use of the cryptographic protections to the JWT. In such cases, the use of the
"none" algorithm can be perfectly acceptable. The "none" algorithm "none" algorithm can be perfectly acceptable. The "none" algorithm
should only be used when the JWT is cryptographically protected by should only be used when the JWT is cryptographically protected by
other means. JWTs using "none" are often used in application other means. JWTs using "none" are often used in application
contexts in which the content is optionally signed; then the URL-safe contexts in which the content is optionally signed; then, the URL-
claims representation and processing can be the same in both the safe claims representation and processing can be the same in both the
signed and unsigned cases. JWT libraries SHOULD NOT generate JWTs signed and unsigned cases. JWT libraries SHOULD NOT generate JWTs
using "none" unless explicitly requested to do by the caller. using "none" unless explicitly requested to do so by the caller.
Similarly, JWT libraries SHOULD NOT consume JWTs using "none" unless Similarly, JWT libraries SHOULD NOT consume JWTs using "none" unless
explicitly requested by the caller. explicitly requested by the caller.
Applications SHOULD follow these algorithm-specific recommendations: Applications SHOULD follow these algorithm-specific recommendations:
- Avoid all RSA-PKCS1 v1.5 encryption algorithms ([RFC8017], Sec. * Avoid all RSA-PKCS1 v1.5 encryption algorithms ([RFC8017],
7.2}, preferring RSA-OAEP ([RFC8017], Sec. 7.1). Section 7.2), preferring RSAES-OAEP ([RFC8017], Section 7.1).
- ECDSA signatures [ANSI-X962-2005] require a unique random value * Elliptic Curve Digital Signature Algorithm (ECDSA) signatures
for every message that is signed. If even just a few bits of the [ANSI-X962-2005] require a unique random value for every message
random value are predictable across multiple messages then the that is signed. If even just a few bits of the random value are
security of the signature scheme may be compromised. In the worst predictable across multiple messages, then the security of the
case, the private key may be recoverable by an attacker. To signature scheme may be compromised. In the worst case, the
counter these attacks, JWT libraries SHOULD implement ECDSA using private key may be recoverable by an attacker. To counter these
the deterministic approach defined in [RFC6979]. This approach is attacks, JWT libraries SHOULD implement ECDSA using the
deterministic approach defined in [RFC6979]. This approach is
completely compatible with existing ECDSA verifiers and so can be completely compatible with existing ECDSA verifiers and so can be
implemented without new algorithm identifiers being required. implemented without new algorithm identifiers being required.
3.3. Validate All Cryptographic Operations 3.3. Validate All Cryptographic Operations
All cryptographic operations used in the JWT MUST be validated and All cryptographic operations used in the JWT MUST be validated and
the entire JWT MUST be rejected if any of them fail to validate. the entire JWT MUST be rejected if any of them fail to validate.
This is true not only of JWTs with a single set of Header Parameters This is true not only of JWTs with a single set of Header Parameters
but also for Nested JWTs, in which both outer and inner operations but also for Nested JWTs in which both outer and inner operations
MUST be validated using the keys and algorithms supplied by the MUST be validated using the keys and algorithms supplied by the
application. application.
3.4. Validate Cryptographic Inputs 3.4. Validate Cryptographic Inputs
Some cryptographic operations, such as Elliptic Curve Diffie-Hellman Some cryptographic operations, such as Elliptic Curve Diffie-Hellman
key agreement ("ECDH-ES") take inputs that may contain invalid key agreement ("ECDH-ES"), take inputs that may contain invalid
values, such as points not on the specified elliptic curve or other values. This includes points not on the specified elliptic curve or
invalid points (see, e.g. [Valenta], Sec. 7.1). The JWS/JWE library other invalid points (e.g., [Valenta], Section 7.1). The JWS/JWE
itself must validate these inputs before using them or it must use library itself must validate these inputs before using them, or it
underlying cryptographic libraries that do so (or both!). must use underlying cryptographic libraries that do so (or both!).
ECDH-ES ephemeral public key (epk) inputs should be validated Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES) ephemeral
according to the recipient's chosen elliptic curve. For the NIST public key (epk) inputs should be validated according to the
prime-order curves P-256, P-384 and P-521, validation MUST be recipient's chosen elliptic curve. For the NIST prime-order curves
performed according to Section 5.6.2.3.4 "ECC Partial Public-Key P-256, P-384, and P-521, validation MUST be performed according to
Validation Routine" of NIST Special Publication 800-56A revision 3 Section 5.6.2.3.4 (ECC Partial Public-Key Validation Routine) of
[nist-sp-800-56a-r3]. Likewise, if the "X25519" or "X448" [RFC8037] "Recommendation for Pair-Wise Key-Establishment Schemes Using
algorithms are used, then the security considerations in [RFC8037] Discrete Logarithm Cryptography" [nist-sp-800-56a-r3]. If the
apply. "X25519" or "X448" [RFC8037] algorithms are used, then the security
considerations in [RFC8037] apply.
3.5. Ensure Cryptographic Keys have Sufficient Entropy 3.5. Ensure Cryptographic Keys Have Sufficient Entropy
The Key Entropy and Random Values advice in Section 10.1 of [RFC7515] The Key Entropy and Random Values advice in Section 10.1 of [RFC7515]
and the Password Considerations in Section 8.8 of [RFC7518] MUST be and the Password Considerations in Section 8.8 of [RFC7518] MUST be
followed. In particular, human-memorizable passwords MUST NOT be followed. In particular, human-memorizable passwords MUST NOT be
directly used as the key to a keyed-MAC algorithm such as "HS256". directly used as the key to a keyed-MAC algorithm such as "HS256".
Moreover, passwords should only be used to perform key encryption,
rather than content encryption, as described in Section 4.8 of
[RFC7518]. Note that even when used for key encryption, password-
based encryption is still subject to brute-force attacks.
In particular, passwords should only be used to perform key 3.6. Avoid Compression of Encryption Inputs
encryption, rather than content encryption, as described in
Section 4.8 of [RFC7518]. Note that even when used for key
encryption, password-based encryption is still subject to brute-force
attacks.
3.6. Avoid Length-Dependent Encryption Inputs
Compression of data SHOULD NOT be done before encryption, because Compression of data SHOULD NOT be done before encryption, because
such compressed data often reveals information about the plaintext. such compressed data often reveals information about the plaintext.
3.7. Use UTF-8 3.7. Use UTF-8
[RFC7515], [RFC7516], and [RFC7519] all specify that UTF-8 be used [RFC7515], [RFC7516], and [RFC7519] all specify that UTF-8 be used
for encoding and decoding JSON used in Header Parameters and JWT for encoding and decoding JSON used in Header Parameters and JWT
Claims Sets. This is also in line with the latest JSON specification Claims Sets. This is also in line with the latest JSON specification
[RFC8259]. Implementations and applications MUST do this, and not [RFC8259]. Implementations and applications MUST do this and not use
use or admit the use of other Unicode encodings for these purposes. or admit the use of other Unicode encodings for these purposes.
3.8. Validate Issuer and Subject 3.8. Validate Issuer and Subject
When a JWT contains an "iss" (issuer) claim, the application MUST When a JWT contains an "iss" (issuer) claim, the application MUST
validate that the cryptographic keys used for the cryptographic validate that the cryptographic keys used for the cryptographic
operations in the JWT belong to the issuer. If they do not, the operations in the JWT belong to the issuer. If they do not, the
application MUST reject the JWT. application MUST reject the JWT.
The means of determining the keys owned by an issuer is application- The means of determining the keys owned by an issuer is application-
specific. As one example, OpenID Connect [OpenID.Core] issuer values specific. As one example, OpenID Connect [OpenID.Core] issuer values
are "https" URLs that reference a JSON metadata document that are "https" URLs that reference a JSON metadata document that
contains a "jwks_uri" value that is an "https" URL from which the contains a "jwks_uri" value that is an "https" URL from which the
issuer's keys are retrieved as a JWK Set [RFC7517]. This same issuer's keys are retrieved as a JWK Set [RFC7517]. This same
mechanism is used by [RFC8414]. Other applications may use different mechanism is used by [RFC8414]. Other applications may use different
means of binding keys to issuers. means of binding keys to issuers.
Similarly, when the JWT contains a "sub" (subject) claim, the Similarly, when the JWT contains a "sub" (subject) claim, the
application MUST validate that the subject value corresponds to a application MUST validate that the subject value corresponds to a
valid subject and/or issuer/subject pair at the application. This valid subject and/or issuer-subject pair at the application. This
may include confirming that the issuer is trusted by the application. may include confirming that the issuer is trusted by the application.
If the issuer, subject, or the pair are invalid, the application MUST If the issuer, subject, or the pair are invalid, the application MUST
reject the JWT. reject the JWT.
3.9. Use and Validate Audience 3.9. Use and Validate Audience
If the same issuer can issue JWTs that are intended for use by more If the same issuer can issue JWTs that are intended for use by more
than one relying party or application, the JWT MUST contain an "aud" than one relying party or application, the JWT MUST contain an "aud"
(audience) claim that can be used to determine whether the JWT is (audience) claim that can be used to determine whether the JWT is
being used by an intended party or was substituted by an attacker at being used by an intended party or was substituted by an attacker at
an unintended party. an unintended party.
In such cases, the relying party or application MUST validate the In such cases, the relying party or application MUST validate the
audience value and if the audience value is not present or not audience value, and if the audience value is not present or not
associated with the recipient, it MUST reject the JWT. associated with the recipient, it MUST reject the JWT.
3.10. Do Not Trust Received Claims 3.10. Do Not Trust Received Claims
The "kid" (key ID) header is used by the relying application to The "kid" (key ID) header is used by the relying application to
perform key lookup. Applications should ensure that this does not perform key lookup. Applications should ensure that this does not
create SQL or LDAP injection vulnerabilities, by validating and/or create SQL or LDAP injection vulnerabilities by validating and/or
sanitizing the received value. sanitizing the received value.
Similarly, blindly following a "jku" (JWK set URL) or "x5u" (X.509 Similarly, blindly following a "jku" (JWK set URL) or "x5u" (X.509
URL) header, which may contain an arbitrary URL, could result in URL) header, which may contain an arbitrary URL, could result in
server-side request forgery (SSRF) attacks. Applications SHOULD server-side request forgery (SSRF) attacks. Applications SHOULD
protect against such attacks, e.g., by matching the URL to a protect against such attacks, e.g., by matching the URL to a
whitelist of allowed locations, and ensuring no cookies are sent in whitelist of allowed locations and ensuring no cookies are sent in
the GET request. the GET request.
3.11. Use Explicit Typing 3.11. Use Explicit Typing
Sometimes, one kind of JWT can be confused for another. If a Sometimes, one kind of JWT can be confused for another. If a
particular kind of JWT is subject to such confusion, that JWT can particular kind of JWT is subject to such confusion, that JWT can
include an explicit JWT type value, and the validation rules can include an explicit JWT type value, and the validation rules can
specify checking the type. This mechanism can prevent such specify checking the type. This mechanism can prevent such
confusion. Explicit JWT typing is accomplished by using the "typ" confusion. Explicit JWT typing is accomplished by using the "typ"
header parameter. For instance, the [RFC8417] specification uses the Header Parameter. For instance, the [RFC8417] specification uses the
"application/secevent+jwt" media type to perform explicit typing of "application/secevent+jwt" media type to perform explicit typing of
Security Event Tokens (SETs). Security Event Tokens (SETs).
Per the definition of "typ" in Section 4.1.9 of [RFC7515], it is Per the definition of "typ" in Section 4.1.9 of [RFC7515], it is
RECOMMENDED that the "application/" prefix be omitted from the "typ" RECOMMENDED that the "application/" prefix be omitted from the "typ"
value. Therefore, for example, the "typ" value used to explicitly value. Therefore, for example, the "typ" value used to explicitly
include a type for a SET SHOULD be "secevent+jwt". When explicit include a type for a SET SHOULD be "secevent+jwt". When explicit
typing is employed for a JWT, it is RECOMMENDED that a media type typing is employed for a JWT, it is RECOMMENDED that a media type
name of the format "application/example+jwt" be used, where "example" name of the format "application/example+jwt" be used, where "example"
is replaced by the identifier for the specific kind of JWT. is replaced by the identifier for the specific kind of JWT.
When applying explicit typing to a Nested JWT, the "typ" header When applying explicit typing to a Nested JWT, the "typ" Header
parameter containing the explicit type value MUST be present in the Parameter containing the explicit type value MUST be present in the
inner JWT of the Nested JWT (the JWT whose payload is the JWT Claims inner JWT of the Nested JWT (the JWT whose payload is the JWT Claims
Set). In some cases the same "typ" header parameter value will be Set). In some cases, the same "typ" Header Parameter value will be
present in the outer JWT as well, to explicitly type the entire present in the outer JWT as well, to explicitly type the entire
Nested JWT. Nested JWT.
Note that the use of explicit typing may not achieve disambiguation Note that the use of explicit typing may not achieve disambiguation
from existing kinds of JWTs, as the validation rules for existing from existing kinds of JWTs, as the validation rules for existing
kinds JWTs often do not use the "typ" header parameter value. kinds of JWTs often do not use the "typ" Header Parameter value.
Explicit typing is RECOMMENDED for new uses of JWTs. Explicit typing is RECOMMENDED for new uses of JWTs.
3.12. Use Mutually Exclusive Validation Rules for Different Kinds of 3.12. Use Mutually Exclusive Validation Rules for Different Kinds of
JWTs JWTs
Each application of JWTs defines a profile specifying the required Each application of JWTs defines a profile specifying the required
and optional JWT claims and the validation rules associated with and optional JWT claims and the validation rules associated with
them. If more than one kind of JWT can be issued by the same issuer, them. If more than one kind of JWT can be issued by the same issuer,
the validation rules for those JWTs MUST be written such that they the validation rules for those JWTs MUST be written such that they
are mutually exclusive, rejecting JWTs of the wrong kind. To prevent are mutually exclusive, rejecting JWTs of the wrong kind. To prevent
substitution of JWTs from one context into another, application substitution of JWTs from one context into another, application
developers may employ a number of strategies: developers may employ a number of strategies:
- Use explicit typing for different kinds of JWTs. Then the * Use explicit typing for different kinds of JWTs. Then the
distinct "typ" values can be used to differentiate between the distinct "typ" values can be used to differentiate between the
different kinds of JWTs. different kinds of JWTs.
- Use different sets of required claims or different required claim * Use different sets of required claims or different required claim
values. Then the validation rules for one kind of JWT will reject values. Then the validation rules for one kind of JWT will reject
those with different claims or values. those with different claims or values.
- Use different sets of required header parameters or different * Use different sets of required Header Parameters or different
required header parameter values. Then the validation rules for required Header Parameter values. Then the validation rules for
one kind of JWT will reject those with different header parameters one kind of JWT will reject those with different Header Parameters
or values. or values.
- Use different keys for different kinds of JWTs. Then the keys * Use different keys for different kinds of JWTs. Then the keys
used to validate one kind of JWT will fail to validate other kinds used to validate one kind of JWT will fail to validate other kinds
of JWTs. of JWTs.
- Use different "aud" values for different uses of JWTs from the * Use different "aud" values for different uses of JWTs from the
same issuer. Then audience validation will reject JWTs same issuer. Then audience validation will reject JWTs
substituted into inappropriate contexts. substituted into inappropriate contexts.
- Use different issuers for different kinds of JWTs. Then the * Use different issuers for different kinds of JWTs. Then the
distinct "iss" values can be used to segregate the different kinds distinct "iss" values can be used to segregate the different kinds
of JWTs. of JWTs.
Given the broad diversity of JWT usage and applications, the best Given the broad diversity of JWT usage and applications, the best
combination of types, required claims, values, header parameters, key combination of types, required claims, values, Header Parameters, key
usages, and issuers to differentiate among different kinds of JWTs usages, and issuers to differentiate among different kinds of JWTs
will, in general, be application specific. As discussed in will, in general, be application-specific. As discussed in
Section 3.11, for new JWT applications, the use of explicit typing is Section 3.11, for new JWT applications, the use of explicit typing is
RECOMMENDED. RECOMMENDED.
4. Security Considerations 4. Security Considerations
This entire document is about security considerations when This entire document is about security considerations when
implementing and deploying JSON Web Tokens. implementing and deploying JSON Web Tokens.
5. IANA Considerations 5. IANA Considerations
This document requires no IANA actions. This document has no IANA actions.
6. Acknowledgements
Thanks to Antonio Sanso for bringing the "ECDH-ES" invalid point
attack to the attention of JWE and JWT implementers. Tim McLean
[McLean] published the RSA/HMAC confusion attack. Thanks to Nat
Sakimura for advocating the use of explicit typing. Thanks to Neil
Madden for his numerous comments, and to Carsten Bormann, Brian
Campbell, Brian Carpenter, Alissa Cooper, Roman Danyliw, Ben Kaduk,
Mirja Kuehlewind, Barry Leiba, Eric Rescorla, Adam Roach, Martin
Vigoureux, and Eric Vyncke for their reviews.
7. References 6. References
7.1. Normative References 6.1. Normative References
[nist-sp-800-56a-r3] [nist-sp-800-56a-r3]
Barker, E., Chen, L., Keller, S., Roginsky, A., Vassilev, Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
A., and R. Davis, "Recommendation for Pair-Wise Key Davis, "Recommendation for Pair-Wise Key-Establishment
Establishment Schemes Using Discrete Logarithm Schemes Using Discrete Logarithm Cryptography", NIST
Cryptography, Draft NIST Special Publication 800-56A Special Publication 800-56A Revision 3,
Revision 3", April 2018, DOI 10.6028/NIST.SP.800-56Ar3, April 2018,
<https://doi.org/10.6028/NIST.SP.800-56Ar3>. <https://doi.org/10.6028/NIST.SP.800-56Ar3>.
[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>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature [RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
skipping to change at page 13, line 28 skipping to change at line 576
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259, Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017, DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>. <https://www.rfc-editor.org/info/rfc8259>.
7.2. Informative References 6.2. Informative References
[Alawatugoda] [Alawatugoda]
Alawatugoda, J., Stebila, D., and C. Boyd, "Protecting Alawatugoda, J., Stebila, D., and C. Boyd, "Protecting
Encrypted Cookies from Compression Side-Channel Attacks", Encrypted Cookies from Compression Side-Channel Attacks",
Financial Cryptography and Data Security pp. 86-106, Financial Cryptography and Data Security, pp. 86-106,
DOI 10.1007/978-3-662-47854-7_6, 2015. DOI 10.1007/978-3-662-47854-7_6, July 2015,
<https://doi.org/10.1007/978-3-662-47854-7_6>.
[ANSI-X962-2005] [ANSI-X962-2005]
"American National Standard X9.62: The Elliptic Curve American National Standards Institute, "Public Key
Digital Signature Algorithm (ECDSA)", November 2005. Cryptography for the Financial Services Industry: the
Elliptic Curve Digital Signature Algorithm (ECDSA)",
ANSI X9.62-2005, November 2005.
[CVE-2015-9235]
NIST, "CVE-2015-9235 Detail", National Vulnerability
Database, May 2018,
<https://nvd.nist.gov/vuln/detail/CVE-2015-9235>.
[Kelsey] Kelsey, J., "Compression and Information Leakage of [Kelsey] Kelsey, J., "Compression and Information Leakage of
Plaintext", Fast Software Encryption pp. 263-276, Plaintext", Fast Software Encryption, pp. 263-276,
DOI 10.1007/3-540-45661-9_21, 2002. DOI 10.1007/3-540-45661-9_21, July 2002,
<https://doi.org/10.1007/3-540-45661-9_21>.
[Langkemper] [Langkemper]
Langkemper, S., "Attacking JWT Authentication", September Langkemper, S., "Attacking JWT authentication", September
2016, <https://www.sjoerdlangkemper.nl/2016/09/28/ 2016, <https://www.sjoerdlangkemper.nl/2016/09/28/
attacking-jwt-authentication/>. attacking-jwt-authentication/>.
[McLean] McLean, T., "Critical vulnerabilities in JSON Web Token [McLean] McLean, T., "Critical vulnerabilities in JSON Web Token
libraries", March 2015, <https://auth0.com/blog/critical- libraries", March 2015, <https://auth0.com/blog/critical-
vulnerabilities-in-json-web-token-libraries//>. vulnerabilities-in-json-web-token-libraries/>.
[OpenID.Core] [OpenID.Core]
Sakimura, N., Bradley, J., Jones, M., Medeiros, B., and C. Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
Mortimore, "OpenID Connect Core 1.0", November 2014, C. Mortimore, "OpenID Connect Core 1.0 incorporating
<http://openid.net/specs/openid-connect-core-1_0.html>. errata set 1", November 2014,
<https://openid.net/specs/openid-connect-core-1_0.html>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012, RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>. <https://www.rfc-editor.org/info/rfc6749>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>. 2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
skipping to change at page 15, line 5 skipping to change at line 648
[Sanso] Sanso, A., "Critical Vulnerability Uncovered in JSON [Sanso] Sanso, A., "Critical Vulnerability Uncovered in JSON
Encryption", March 2017, Encryption", March 2017,
<https://blogs.adobe.com/security/2017/03/critical- <https://blogs.adobe.com/security/2017/03/critical-
vulnerability-uncovered-in-json-encryption.html>. vulnerability-uncovered-in-json-encryption.html>.
[Valenta] Valenta, L., Sullivan, N., Sanso, A., and N. Heninger, "In [Valenta] Valenta, L., Sullivan, N., Sanso, A., and N. Heninger, "In
search of CurveSwap: Measuring elliptic curve search of CurveSwap: Measuring elliptic curve
implementations in the wild", March 2018, implementations in the wild", March 2018,
<https://ia.cr/2018/298>. <https://ia.cr/2018/298>.
Appendix A. Document History Acknowledgements
[[ to be removed by the RFC editor before publication as an RFC ]]
A.1. draft-ietf-oauth-jwt-bcp-07
- IESG review comments.
A.2. draft-ietf-oauth-jwt-bcp-06
- Second AD review.
- Removed unworkable recommendation to pad encrypted passwords.
A.3. draft-ietf-oauth-jwt-bcp-05
- Genart review comments.
A.4. draft-ietf-oauth-jwt-bcp-04
- AD review comments.
A.5. draft-ietf-oauth-jwt-bcp-03
- Acknowledgements.
A.6. draft-ietf-oauth-jwt-bcp-02
- Implemented WGLC feedback.
A.7. draft-ietf-oauth-jwt-bcp-01
- Feedback from Brian Campbell.
A.8. draft-ietf-oauth-jwt-bcp-00
- Initial WG draft. No change from the latest individual version.
A.9. draft-sheffer-oauth-jwt-bcp-01
- Added explicit typing.
A.10. draft-sheffer-oauth-jwt-bcp-00
- Initial version. Thanks to Antonio Sanso for bringing the "ECDH-ES" invalid point
attack to the attention of JWE and JWT implementers. Tim McLean
published the RSA/HMAC confusion attack [McLean]. Thanks to Nat
Sakimura for advocating the use of explicit typing. Thanks to Neil
Madden for his numerous comments, and to Carsten Bormann, Brian
Campbell, Brian Carpenter, Alissa Cooper, Roman Danyliw, Ben Kaduk,
Mirja Kühlewind, Barry Leiba, Eric Rescorla, Adam Roach, Martin
Vigoureux, and Éric Vyncke for their reviews.
Authors' Addresses Authors' Addresses
Yaron Sheffer Yaron Sheffer
Intuit Intuit
EMail: yaronf.ietf@gmail.com Email: yaronf.ietf@gmail.com
Dick Hardt Dick Hardt
EMail: dick.hardt@gmail.com Email: dick.hardt@gmail.com
Michael B. Jones Michael B. Jones
Microsoft Microsoft
EMail: mbj@microsoft.com Email: mbj@microsoft.com
URI: http://self-issued.info/ URI: https://self-issued.info/
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