RFC 7518
JSON Web Algorithms (JWA)
Internet Engineering Task Force (IETF) M. Jones Request for Comments: 7518 Microsoft Category: Standards Track May 2015 ISSN: 2070-1721 JSON Web Algorithms (JWA)Abstract
This specification registers cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. 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/rfc7518. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Cryptographic Algorithms for Digital Signatures and MACs . . 6 3.1. "alg" (Algorithm) Header Parameter Values for JWS . . . . 6 3.2. HMAC with SHA-2 Functions . . . . . . . . . . . . . . . . 7 3.3. Digital Signature with RSASSA-PKCS1-v1_5 . . . . . . . . 8 3.4. Digital Signature with ECDSA . . . . . . . . . . . . . . 9 3.5. Digital Signature with RSASSA-PSS . . . . . . . . . . . . 10 3.6. Using the Algorithm "none" . . . . . . . . . . . . . . . 11 4. Cryptographic Algorithms for Key Management . . . . . . . . . 11 4.1. "alg" (Algorithm) Header Parameter Values for JWE . . . . 12 4.2. Key Encryption with RSAES-PKCS1-v1_5 . . . . . . . . . . 13 4.3. Key Encryption with RSAES OAEP . . . . . . . . . . . . . 14 4.4. Key Wrapping with AES Key Wrap . . . . . . . . . . . . . 14 4.5. Direct Encryption with a Shared Symmetric Key . . . . . . 15 4.6. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES) . . . . . . . . . . . . . . . 15 4.6.1. Header Parameters Used for ECDH Key Agreement . . . . 16 4.6.1.1. "epk" (Ephemeral Public Key) Header Parameter . . 16 4.6.1.2. "apu" (Agreement PartyUInfo) Header Parameter . . 17 4.6.1.3. "apv" (Agreement PartyVInfo) Header Parameter . . 17 4.6.2. Key Derivation for ECDH Key Agreement . . . . . . . . 17 4.7. Key Encryption with AES GCM . . . . . . . . . . . . . . . 18 4.7.1. Header Parameters Used for AES GCM Key Encryption . . 19 4.7.1.1. "iv" (Initialization Vector) Header Parameter . . 19 4.7.1.2. "tag" (Authentication Tag) Header Parameter . . . 19 4.8. Key Encryption with PBES2 . . . . . . . . . . . . . . . . 20 4.8.1. Header Parameters Used for PBES2 Key Encryption . . . 20 4.8.1.1. "p2s" (PBES2 Salt Input) Header Parameter . . . . 21 4.8.1.2. "p2c" (PBES2 Count) Header Parameter . . . . . . 21 5. Cryptographic Algorithms for Content Encryption . . . . . . . 21 5.1. "enc" (Encryption Algorithm) Header Parameter Values for JWE . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.2. AES_CBC_HMAC_SHA2 Algorithms . . . . . . . . . . . . . . 22 5.2.1. Conventions Used in Defining AES_CBC_HMAC_SHA2 . . . 23 5.2.2. Generic AES_CBC_HMAC_SHA2 Algorithm . . . . . . . . . 23 5.2.2.1. AES_CBC_HMAC_SHA2 Encryption . . . . . . . . . . 23 5.2.2.2. AES_CBC_HMAC_SHA2 Decryption . . . . . . . . . . 25 5.2.3. AES_128_CBC_HMAC_SHA_256 . . . . . . . . . . . . . . 25 5.2.4. AES_192_CBC_HMAC_SHA_384 . . . . . . . . . . . . . . 26 5.2.5. AES_256_CBC_HMAC_SHA_512 . . . . . . . . . . . . . . 26 5.2.6. Content Encryption with AES_CBC_HMAC_SHA2 . . . . . . 26 5.3. Content Encryption with AES GCM . . . . . . . . . . . . . 27 6. Cryptographic Algorithms for Keys . . . . . . . . . . . . . . 27 6.1. "kty" (Key Type) Parameter Values . . . . . . . . . . . . 28
6.2. Parameters for Elliptic Curve Keys . . . . . . . . . . . 28
6.2.1. Parameters for Elliptic Curve Public Keys . . . . . . 28
6.2.1.1. "crv" (Curve) Parameter . . . . . . . . . . . . . 28
6.2.1.2. "x" (X Coordinate) Parameter . . . . . . . . . . 29
6.2.1.3. "y" (Y Coordinate) Parameter . . . . . . . . . . 29
6.2.2. Parameters for Elliptic Curve Private Keys . . . . . 29
6.2.2.1. "d" (ECC Private Key) Parameter . . . . . . . . . 29
6.3. Parameters for RSA Keys . . . . . . . . . . . . . . . . . 30
6.3.1. Parameters for RSA Public Keys . . . . . . . . . . . 30
6.3.1.1. "n" (Modulus) Parameter . . . . . . . . . . . . . 30
6.3.1.2. "e" (Exponent) Parameter . . . . . . . . . . . . 30
6.3.2. Parameters for RSA Private Keys . . . . . . . . . . . 30
6.3.2.1. "d" (Private Exponent) Parameter . . . . . . . . 30
6.3.2.2. "p" (First Prime Factor) Parameter . . . . . . . 31
6.3.2.3. "q" (Second Prime Factor) Parameter . . . . . . . 31
6.3.2.4. "dp" (First Factor CRT Exponent) Parameter . . . 31
6.3.2.5. "dq" (Second Factor CRT Exponent) Parameter . . . 31
6.3.2.6. "qi" (First CRT Coefficient) Parameter . . . . . 31
6.3.2.7. "oth" (Other Primes Info) Parameter . . . . . . . 31
6.4. Parameters for Symmetric Keys . . . . . . . . . . . . . . 32
6.4.1. "k" (Key Value) Parameter . . . . . . . . . . . . . . 32
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
7.1. JSON Web Signature and Encryption Algorithms Registry . . 33
7.1.1. Registration Template . . . . . . . . . . . . . . . . 34
7.1.2. Initial Registry Contents . . . . . . . . . . . . . . 35
7.2. Header Parameter Names Registration . . . . . . . . . . . 42
7.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 42
7.3. JSON Web Encryption Compression Algorithms Registry . . . 43
7.3.1. Registration Template . . . . . . . . . . . . . . . . 43
7.3.2. Initial Registry Contents . . . . . . . . . . . . . . 44
7.4. JSON Web Key Types Registry . . . . . . . . . . . . . . . 44
7.4.1. Registration Template . . . . . . . . . . . . . . . . 44
7.4.2. Initial Registry Contents . . . . . . . . . . . . . . 45
7.5. JSON Web Key Parameters Registration . . . . . . . . . . 45
7.5.1. Registry Contents . . . . . . . . . . . . . . . . . . 46
7.6. JSON Web Key Elliptic Curve Registry . . . . . . . . . . 48
7.6.1. Registration Template . . . . . . . . . . . . . . . . 48
7.6.2. Initial Registry Contents . . . . . . . . . . . . . . 49
8. Security Considerations . . . . . . . . . . . . . . . . . . . 49
8.1. Cryptographic Agility . . . . . . . . . . . . . . . . . . 50
8.2. Key Lifetimes . . . . . . . . . . . . . . . . . . . . . . 50
8.3. RSAES-PKCS1-v1_5 Security Considerations . . . . . . . . 50
8.4. AES GCM Security Considerations . . . . . . . . . . . . . 50
8.5. Unsecured JWS Security Considerations . . . . . . . . . . 51
8.6. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 51
8.7. Reusing Key Material when Encrypting Keys . . . . . . . . 51
8.8. Password Considerations . . . . . . . . . . . . . . . . . 52
8.9. Key Entropy and Random Values . . . . . . . . . . . . . . 52
8.10. Differences between Digital Signatures and MACs . . . . . 52
8.11. Using Matching Algorithm Strengths . . . . . . . . . . . 53
8.12. Adaptive Chosen-Ciphertext Attacks . . . . . . . . . . . 53
8.13. Timing Attacks . . . . . . . . . . . . . . . . . . . . . 53
8.14. RSA Private Key Representations and Blinding . . . . . . 53
9. Internationalization Considerations . . . . . . . . . . . . . 53
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
10.1. Normative References . . . . . . . . . . . . . . . . . . 53
10.2. Informative References . . . . . . . . . . . . . . . . . 56
Appendix A. Algorithm Identifier Cross-Reference . . . . . . . . 59
A.1. Digital Signature/MAC Algorithm Identifier Cross-
Reference . . . . . . . . . . . . . . . . . . . . . . . . 60
A.2. Key Management Algorithm Identifier Cross-Reference . . . 61
A.3. Content Encryption Algorithm Identifier Cross-Reference . 62
Appendix B. Test Cases for AES_CBC_HMAC_SHA2 Algorithms . . . . 62
B.1. Test Cases for AES_128_CBC_HMAC_SHA_256 . . . . . . . . . 63
B.2. Test Cases for AES_192_CBC_HMAC_SHA_384 . . . . . . . . . 64
B.3. Test Cases for AES_256_CBC_HMAC_SHA_512 . . . . . . . . . 65
Appendix C. Example ECDH-ES Key Agreement Computation . . . . . 66
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 69
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 69
1. Introduction
This specification registers cryptographic algorithms and identifiers
to be used with the JSON Web Signature (JWS) [JWS], JSON Web
Encryption (JWE) [JWE], and JSON Web Key (JWK) [JWK] specifications.
It defines several IANA registries for these identifiers. All these
specifications utilize JSON-based [RFC7159] data structures. This
specification also describes the semantics and operations that are
specific to these algorithms and key types.
Registering the algorithms and identifiers here, rather than in the
JWS, JWE, and JWK specifications, is intended to allow them to remain
unchanged in the face of changes in the set of Required, Recommended,
Optional, and Deprecated algorithms over time. This also allows
changes to the JWS, JWE, and JWK specifications without changing this
document.
Names defined by this specification are short because a core goal is
for the resulting representations to be compact.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
"Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
The interpretation should only be applied when the terms appear in all capital letters. BASE64URL(OCTETS) denotes the base64url encoding of OCTETS, per Section 2 of [JWS]. UTF8(STRING) denotes the octets of the UTF-8 [RFC3629] representation of STRING, where STRING is a sequence of zero or more Unicode [UNICODE] characters. ASCII(STRING) denotes the octets of the ASCII [RFC20] representation of STRING, where STRING is a sequence of zero or more ASCII characters. The concatenation of two values A and B is denoted as A || B.2. Terminology
The terms "JSON Web Signature (JWS)", "Base64url Encoding", "Header Parameter", "JOSE Header", "JWS Payload", "JWS Protected Header", "JWS Signature", "JWS Signing Input", and "Unsecured JWS" are defined by the JWS specification [JWS]. The terms "JSON Web Encryption (JWE)", "Additional Authenticated Data (AAD)", "Authentication Tag", "Content Encryption Key (CEK)", "Direct Encryption", "Direct Key Agreement", "JWE Authentication Tag", "JWE Ciphertext", "JWE Encrypted Key", "JWE Initialization Vector", "JWE Protected Header", "Key Agreement with Key Wrapping", "Key Encryption", "Key Management Mode", and "Key Wrapping" are defined by the JWE specification [JWE]. The terms "JSON Web Key (JWK)" and "JWK Set" are defined by the JWK specification [JWK]. The terms "Ciphertext", "Digital Signature", "Initialization Vector", "Message Authentication Code (MAC)", and "Plaintext" are defined by the "Internet Security Glossary, Version 2" [RFC4949]. This term is defined by this specification: Base64urlUInt The representation of a positive or zero integer value as the base64url encoding of the value's unsigned big-endian representation as an octet sequence. The octet sequence MUST utilize the minimum number of octets needed to represent the value. Zero is represented as BASE64URL(single zero-valued octet), which is "AA".
3. Cryptographic Algorithms for Digital Signatures and MACs
JWS uses cryptographic algorithms to digitally sign or create a MAC of the contents of the JWS Protected Header and the JWS Payload.3.1. "alg" (Algorithm) Header Parameter Values for JWS
The table below is the set of "alg" (algorithm) Header Parameter values defined by this specification for use with JWS, each of which is explained in more detail in the following sections: +--------------+-------------------------------+--------------------+ | "alg" Param | Digital Signature or MAC | Implementation | | Value | Algorithm | Requirements | +--------------+-------------------------------+--------------------+ | HS256 | HMAC using SHA-256 | Required | | HS384 | HMAC using SHA-384 | Optional | | HS512 | HMAC using SHA-512 | Optional | | RS256 | RSASSA-PKCS1-v1_5 using | Recommended | | | SHA-256 | | | RS384 | RSASSA-PKCS1-v1_5 using | Optional | | | SHA-384 | | | RS512 | RSASSA-PKCS1-v1_5 using | Optional | | | SHA-512 | | | ES256 | ECDSA using P-256 and SHA-256 | Recommended+ | | ES384 | ECDSA using P-384 and SHA-384 | Optional | | ES512 | ECDSA using P-521 and SHA-512 | Optional | | PS256 | RSASSA-PSS using SHA-256 and | Optional | | | MGF1 with SHA-256 | | | PS384 | RSASSA-PSS using SHA-384 and | Optional | | | MGF1 with SHA-384 | | | PS512 | RSASSA-PSS using SHA-512 and | Optional | | | MGF1 with SHA-512 | | | none | No digital signature or MAC | Optional | | | performed | | +--------------+-------------------------------+--------------------+ The use of "+" in the Implementation Requirements column indicates that the requirement strength is likely to be increased in a future version of the specification. See Appendix A.1 for a table cross-referencing the JWS digital signature and MAC "alg" (algorithm) values defined in this specification with the equivalent identifiers used by other standards and software packages.
3.2. HMAC with SHA-2 Functions
Hash-based Message Authentication Codes (HMACs) enable one to use a secret plus a cryptographic hash function to generate a MAC. This can be used to demonstrate that whoever generated the MAC was in possession of the MAC key. The algorithm for implementing and validating HMACs is provided in RFC 2104 [RFC2104]. A key of the same size as the hash output (for instance, 256 bits for "HS256") or larger MUST be used with this algorithm. (This requirement is based on Section 5.3.4 (Security Effect of the HMAC Key) of NIST SP 800-117 [NIST.800-107], which states that the effective security strength is the minimum of the security strength of the key and two times the size of the internal hash value.) The HMAC SHA-256 MAC is generated per RFC 2104, using SHA-256 as the hash algorithm "H", using the JWS Signing Input as the "text" value, and using the shared key. The HMAC output value is the JWS Signature. The following "alg" (algorithm) Header Parameter values are used to indicate that the JWS Signature is an HMAC value computed using the corresponding algorithm: +-------------------+--------------------+ | "alg" Param Value | MAC Algorithm | +-------------------+--------------------+ | HS256 | HMAC using SHA-256 | | HS384 | HMAC using SHA-384 | | HS512 | HMAC using SHA-512 | +-------------------+--------------------+ The HMAC SHA-256 MAC for a JWS is validated by computing an HMAC value per RFC 2104, using SHA-256 as the hash algorithm "H", using the received JWS Signing Input as the "text" value, and using the shared key. This computed HMAC value is then compared to the result of base64url decoding the received encoded JWS Signature value. The comparison of the computed HMAC value to the JWS Signature value MUST be done in a constant-time manner to thwart timing attacks. Alternatively, the computed HMAC value can be base64url encoded and compared to the received encoded JWS Signature value (also in a constant-time manner), as this comparison produces the same result as comparing the unencoded values. In either case, if the values match, the HMAC has been validated.
Securing content and validation with the HMAC SHA-384 and HMAC SHA-512 algorithms is performed identically to the procedure for HMAC SHA-256 -- just using the corresponding hash algorithms with correspondingly larger minimum key sizes and result values: 384 bits each for HMAC SHA-384 and 512 bits each for HMAC SHA-512. An example using this algorithm is shown in Appendix A.1 of [JWS].3.3. Digital Signature with RSASSA-PKCS1-v1_5
This section defines the use of the RSASSA-PKCS1-v1_5 digital signature algorithm as defined in Section 8.2 of RFC 3447 [RFC3447] (commonly known as PKCS #1), using SHA-2 [SHS] hash functions. A key of size 2048 bits or larger MUST be used with these algorithms. The RSASSA-PKCS1-v1_5 SHA-256 digital signature is generated as follows: generate a digital signature of the JWS Signing Input using RSASSA-PKCS1-v1_5-SIGN and the SHA-256 hash function with the desired private key. This is the JWS Signature value. The following "alg" (algorithm) Header Parameter values are used to indicate that the JWS Signature is a digital signature value computed using the corresponding algorithm: +-------------------+---------------------------------+ | "alg" Param Value | Digital Signature Algorithm | +-------------------+---------------------------------+ | RS256 | RSASSA-PKCS1-v1_5 using SHA-256 | | RS384 | RSASSA-PKCS1-v1_5 using SHA-384 | | RS512 | RSASSA-PKCS1-v1_5 using SHA-512 | +-------------------+---------------------------------+ The RSASSA-PKCS1-v1_5 SHA-256 digital signature for a JWS is validated as follows: submit the JWS Signing Input, the JWS Signature, and the public key corresponding to the private key used by the signer to the RSASSA-PKCS1-v1_5-VERIFY algorithm using SHA-256 as the hash function. Signing and validation with the RSASSA-PKCS1-v1_5 SHA-384 and RSASSA- PKCS1-v1_5 SHA-512 algorithms is performed identically to the procedure for RSASSA-PKCS1-v1_5 SHA-256 -- just using the corresponding hash algorithms instead of SHA-256. An example using this algorithm is shown in Appendix A.2 of [JWS].
3.4. Digital Signature with ECDSA
The Elliptic Curve Digital Signature Algorithm (ECDSA) [DSS] provides for the use of Elliptic Curve Cryptography, which is able to provide equivalent security to RSA cryptography but using shorter key sizes and with greater processing speed for many operations. This means that ECDSA digital signatures will be substantially smaller in terms of length than equivalently strong RSA digital signatures. This specification defines the use of ECDSA with the P-256 curve and the SHA-256 cryptographic hash function, ECDSA with the P-384 curve and the SHA-384 hash function, and ECDSA with the P-521 curve and the SHA-512 hash function. The P-256, P-384, and P-521 curves are defined in [DSS]. The ECDSA P-256 SHA-256 digital signature is generated as follows: 1. Generate a digital signature of the JWS Signing Input using ECDSA P-256 SHA-256 with the desired private key. The output will be the pair (R, S), where R and S are 256-bit unsigned integers. 2. Turn R and S into octet sequences in big-endian order, with each array being be 32 octets long. The octet sequence representations MUST NOT be shortened to omit any leading zero octets contained in the values. 3. Concatenate the two octet sequences in the order R and then S. (Note that many ECDSA implementations will directly produce this concatenation as their output.) 4. The resulting 64-octet sequence is the JWS Signature value. The following "alg" (algorithm) Header Parameter values are used to indicate that the JWS Signature is a digital signature value computed using the corresponding algorithm: +-------------------+-------------------------------+ | "alg" Param Value | Digital Signature Algorithm | +-------------------+-------------------------------+ | ES256 | ECDSA using P-256 and SHA-256 | | ES384 | ECDSA using P-384 and SHA-384 | | ES512 | ECDSA using P-521 and SHA-512 | +-------------------+-------------------------------+
The ECDSA P-256 SHA-256 digital signature for a JWS is validated as
follows:
1. The JWS Signature value MUST be a 64-octet sequence. If it is
not a 64-octet sequence, the validation has failed.
2. Split the 64-octet sequence into two 32-octet sequences. The
first octet sequence represents R and the second S. The values R
and S are represented as octet sequences using the Integer-to-
OctetString Conversion defined in Section 2.3.7 of SEC1 [SEC1]
(in big-endian octet order).
3. Submit the JWS Signing Input, R, S, and the public key (x, y) to
the ECDSA P-256 SHA-256 validator.
Signing and validation with the ECDSA P-384 SHA-384 and ECDSA P-521
SHA-512 algorithms is performed identically to the procedure for
ECDSA P-256 SHA-256 -- just using the corresponding hash algorithms
with correspondingly larger result values. For ECDSA P-384 SHA-384,
R and S will be 384 bits each, resulting in a 96-octet sequence. For
ECDSA P-521 SHA-512, R and S will be 521 bits each, resulting in a
132-octet sequence. (Note that the Integer-to-OctetString Conversion
defined in Section 2.3.7 of SEC1 [SEC1] used to represent R and S as
octet sequences adds zero-valued high-order padding bits when needed
to round the size up to a multiple of 8 bits; thus, each 521-bit
integer is represented using 528 bits in 66 octets.)
Examples using these algorithms are shown in Appendices A.3 and A.4
of [JWS].
3.5. Digital Signature with RSASSA-PSS
This section defines the use of the RSASSA-PSS digital signature
algorithm as defined in Section 8.1 of RFC 3447 [RFC3447] with the
MGF1 mask generation function and SHA-2 hash functions, always using
the same hash function for both the RSASSA-PSS hash function and the
MGF1 hash function. The size of the salt value is the same size as
the hash function output. All other algorithm parameters use the
defaults specified in Appendix A.2.3 of RFC 3447.
A key of size 2048 bits or larger MUST be used with this algorithm.
The RSASSA-PSS SHA-256 digital signature is generated as follows:
generate a digital signature of the JWS Signing Input using RSASSA-
PSS-SIGN, the SHA-256 hash function, and the MGF1 mask generation
function with SHA-256 with the desired private key. This is the JWS
Signature value.
The following "alg" (algorithm) Header Parameter values are used to indicate that the JWS Signature is a digital signature value computed using the corresponding algorithm: +-------------------+-----------------------------------------------+ | "alg" Param Value | Digital Signature Algorithm | +-------------------+-----------------------------------------------+ | PS256 | RSASSA-PSS using SHA-256 and MGF1 with | | | SHA-256 | | PS384 | RSASSA-PSS using SHA-384 and MGF1 with | | | SHA-384 | | PS512 | RSASSA-PSS using SHA-512 and MGF1 with | | | SHA-512 | +-------------------+-----------------------------------------------+ The RSASSA-PSS SHA-256 digital signature for a JWS is validated as follows: submit the JWS Signing Input, the JWS Signature, and the public key corresponding to the private key used by the signer to the RSASSA-PSS-VERIFY algorithm using SHA-256 as the hash function and using MGF1 as the mask generation function with SHA-256. Signing and validation with the RSASSA-PSS SHA-384 and RSASSA-PSS SHA-512 algorithms is performed identically to the procedure for RSASSA-PSS SHA-256 -- just using the alternative hash algorithm in both roles.3.6. Using the Algorithm "none"
JWSs MAY also be created that do not provide integrity protection. Such a JWS is called an Unsecured JWS. An Unsecured JWS uses the "alg" value "none" and is formatted identically to other JWSs, but MUST use the empty octet sequence as its JWS Signature value. Recipients MUST verify that the JWS Signature value is the empty octet sequence. Implementations that support Unsecured JWSs MUST NOT accept such objects as valid unless the application specifies that it is acceptable for a specific object to not be integrity protected. Implementations MUST NOT accept Unsecured JWSs by default. In order to mitigate downgrade attacks, applications MUST NOT signal acceptance of Unsecured JWSs at a global level, and SHOULD signal acceptance on a per-object basis. See Section 8.5 for security considerations associated with using this algorithm.
(page 11 continued on part 2)
