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Security XMLSEC XMLDSIG XMLENC DigestMethod SigntureMethod EncryptionMethod AgreementMethod KeyDerivationMethod KeyInfo This document updates and corrects the IANA "XML Security URIs" registry that lists URIs intended for use with XML digital signatures, encryption, canonicalization, and key management. These URIs identify algorithms and types of information. This document also obsoletes RFC 9231.

Introduction XML digital signatures, canonicalization, and encryption were standardized by the W3C and by the joint IETF/W3C XMLDSIG working group . These are now W3C Recommendations and some are also RFCs. They are available as follows:

RFC Status	W3C REC	Topic
Draft Standard		XML Digital Signatures
Informational		Canonical XML
- - - - - -		XML Encryption 1.0
Informational		Exclusive XML Canonicalization 1.0

These documents and recommendations use URIs to identify algorithms and keying information types. The W3C has subsequently produced updated XML Signature 1.1 , Canonical XML 1.1 , and XML Encryption 1.1 versions, as well as a new XML Signature Properties specification . In addition, the XML Encryption recommendation has been augmented by , which defines algorithms, XML types, and elements necessary to use generic hybrid ciphers in XML security applications. also provides for a key encapsulation algorithm and a data encapsulation algorithm, with the combination of the two forming the generic hybrid cipher. All camel-case element names (names with both interior upper and lower case letters) herein, such as DigestValue, are from these documents. This document is an updated convenient reference list of URIs and corresponding algorithms in which there is expressed interest. It includes fixes for Errata [Err3597], [Err3965], and [Err4004], and obsoletes . All of the URIs for algorithms and data types herein are listed in the indexes in . Of these URIs, those that were added by earlier RFCs or by this document have a subsection in Section or . A few URIs defined elsewhere also have a subsection in Section or , but most such URIs do not. For example, use of SHA-256 as defined in has no subsection here but is included in the indexes in . Specification in this document of the URI representing an algorithm does not imply endorsement of the algorithm for any particular purpose. A protocol specification, which this is not, generally gives algorithm and implementation requirements for the protocol. Security considerations for algorithms are constantly evolving, as documented elsewhere. This specification simply provides some URIs and relevant formatting when those URIs are used. This document is not intended to change the algorithm implementation requirements of any IETF or W3C document. Use of terminology from and is intended to be only such as is already stated or implied by other authoritative documents. Progressing XML Digital Signature along the Standards Track required removal of any algorithms from the original version for which there was not demonstrated interoperability. This required removal of the Minimal Canonicalization algorithm, in which there was continued interest. The URI for Minimal Canonicalization was included in and is included here.

Terminology 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 BCP 14 when, and only when, they appear in all capitals, as shown here. "camel-case" refers to terms that are mostly lower case but have internal capital letters.

Acronyms The following acronyms are used in this document:

AAD -

Additional Authenticated Data

AEAD -

Authenticated Encryption with Associated Data

ASN.1 -

Abstract Syntax Notation 1

BER -

Basic Encoding Rules

DSA -

Digital Signature Algorithm

DSS -

Digital Signature Standard

ECDSA -

Elliptic Curve DSA

HMAC -

Hashed Message Authentication Code

IETF -

Internet Engineering Task Force

MAC -

Message Authentication Code

MD -

Message Digest

NIST -

United States National Institute of Standards and Technology

OID -

Object Identifier

PKCS -

Public Key Cryptography Standard

RSA -

Rivest, Shamir, and Adleman

SHA -

Secure Hash Algorithm

URI -

Uniform Resource Identifier

W3C -

World Wide Web Consortium

XML -

eXtensible Markup Language

Algorithms The URI that was dropped from the XML Digital Signature standard due to the transition from Proposed Standard to Draft Standard is included in with its original prefix so as to avoid changing the XMLDSIG standard's namespace. Additional algorithms in RFC 4051 were given URIs that start with Further algorithms added in RFC 6931 were given URIs that start with and algorithms added in this document are given URIs that start with In addition, for ease of reference, this document includes in the indexes in many cryptographic algorithm URIs from XML security documents using the namespaces with which they are defined in those documents as follows: for some URIs specified in , for some URIs specified in , and for some URIs specified in . See also .

DigestMethod (Hash) Algorithms These algorithms are usable wherever a DigestMethod element occurs.

MD5 The MD5 algorithm takes no explicit parameters. An example of an MD5 DigestAlgorithm element is: ]]> An MD5 digest is a 128-bit string. The content of the DigestValue element SHALL be the base64 encoding of this bit string viewed as a 16-octet stream. See for MD5 security considerations.

SHA-224 The SHA-224 algorithm takes no explicit parameters. An example of a SHA-224 DigestAlgorithm element is: ]]> A SHA-224 digest is a 224-bit string. The content of the DigestValue element SHALL be the base64 encoding of this string viewed as a 28-octet stream.

SHA-384 The SHA-384 algorithm takes no explicit parameters. An example of a SHA-384 DigestAlgorithm element is: ]]> A SHA-384 digest is a 384-bit string. The content of the DigestValue element SHALL be the base64 encoding of this string viewed as a 48-octet stream.

Whirlpool The Whirlpool algorithm takes no explicit parameters. An example of a Whirlpool DigestAlgorithm element is: ]]> A Whirlpool digest is a 512-bit string. The content of the DigestValue element SHALL be the base64 encoding of this string viewed as a 64-octet stream.

SHA-3 Algorithms NIST conducted a hash function competition for an alternative to the SHA family. The Keccak-f[1600] algorithm was selected . This hash function is commonly referred to as "SHA-3" . A SHA-3 224, 256, 384, and 512 digest is a 224-, 256-, 384-, and 512-bit string, respectively. The content of the DigestValue element SHALL be the base64 encoding of this string viewed as a 28-, 32-, 48-, and 64-octet stream, respectively. An example of a SHA3-224 DigestAlgorithm element is: ]]>

SignatureMethod MAC Algorithms This section covers SignatureMethod Message Authentication Code (MAC) Algorithms. Note: Some text in this section is duplicated from for the convenience of the reader. is normative in case of conflict.

HMAC-MD5 The HMAC algorithm takes the truncation length in bits as a parameter; if the parameter is not specified, then all the bits of the hash are output. An example of an HMAC-MD5 SignatureMethod element is as follows: 112 ]]> The output of the HMAC algorithm is the output (possibly truncated) of the chosen digest algorithm. This value SHALL be base64 encoded in the same straightforward fashion as the output of the digest algorithms. Example: the SignatureValue element for the HMAC-MD5 digest 9294727A 3638BB1C 13F48EF8 158BFC9D from the test vectors in would be kpRyejY4uxwT9I74FYv8nQ== Schema Definition: ]]> DTD: ]]> The Schema Definition and DTD immediately above are copied from . See for HMAC-MD5 security considerations.

HMAC SHA Variations SHA-224, SHA-256, SHA-384, and SHA-512 can also be used in HMAC as described in for HMAC-MD5.

HMAC-RIPEMD160 RIPEMD-160 is a 160-bit hash that is used here in HMAC. The output can be optionally truncated. An example is as follows: 144 ]]>

Poly1305 Poly1305 is a high-speed message authentication code algorithm. It takes a 32-octet one-time key and a message and produces a 16-octet tag, which is used to authenticate the message. An example of a Poly1305 SignatureMethod element is as follows: ]]>

SipHash-2-4 SipHash computes a 64-bit MAC from a 128-bit secret key and a variable-length message. An example of a SipHash-2-4 SignatureMethod element is as follows: ]]>

XMSS and XMSSMT XMSS (eXtended Merkle Signature Scheme) and XMSSMT (XMSS Multi-Tree) are stateful hash-based signature schemes . According to NIST, it is believed that the security of these schemes depends only on the security of the underlying hash functions, in particular the infeasibility of finding a preimage or a second preimage, and it is believed that the security of these hash functions will not be broken by the development of large-scale quantum computers. For further information on the intended usage of these signature schemes and the careful state management required to maintain their strength, see . IANA maintains a registry whose entries correspond to the XMSS Identifiers below (see ). The fragment part of the URIs is formed by replacing occurrences of underscore ("_") in the name appearing in the IANA registry with hyphen ("-"). The hash functions used in the XMSS signature schemes above are SHA2 or one of the two SHAKE extensible output functions as indicated by the second token of the URI extension (SHAKE means SHAKE128). The tree height for XMSS is 10, 16, or 20 as indicated by the third token of the URI extension. The SHA2 or SHAKE output size is 192, 256, or 512 bits as indicated by the final token of the URI extension. SHA2 with 192 bits of output means SHA2-256/192, that is, the most significant 192 bits of the SHA-256 hash as specified in . IANA maintains a registry whose entries correspond to the XMSSMT Identifiers below (see ). The fragment part of the URIs is formed by replacing occurrences of underscore ("_") and slash ("/") in the name appearing in the IANA registry with hyphen ("-"). The hash functions used in the XMSSMT signature schemes above are SHA2 or one of the two the SHAKE extensible output function as indicated by the second token of the URI extension (SHAKE means SHAKE128). The tree height for XMSSMT is 20, 40, or 60 as indicated by the third token of the URI extension. The number of layers is indicated by a fourth token. The SHA2, SHAKE, or SHAKE256 output size is 192, 256, or 512 bits as indicated by the final token of the URI extension. SHA2 with 192 bits of output means SHA2-256/192, that is, the most significant 192 bits of the SHA-256 hash as specified in . An example of an XMSS SignatureAlgorithm element is: ]]>

SignatureMethod Public Key Signature Algorithms These algorithms are distinguished from those in in that they use public key methods. That is to say, the signing key is different from and not feasibly derivable from the verification key.

RSA-MD5 This implies the PKCS #1 v1.5 padding algorithm described in . An example of use is: ]]> The SignatureValue content for an RSA-MD5 signature is the base64 encoding of the octet string computed as per , signature generation for the RSASSA-PKCS1-v1_5 signature scheme. As specified in the EMSA-PKCS1-V1_5-ENCODE function in , the value input to the signature function MUST contain a prepended algorithm object identifier for the hash function, but the availability of an ASN.1 parser and recognition of OIDs is not required of a signature verifier. The PKCS #1 v1.5 representation appears as: The padded ASN.1 will be of the following form: The vertical bar ("|") represents concatenation. "01", "FF", and "00" are fixed octets of the corresponding hexadecimal value, and the asterisk ("*") after "FF" indicates repetition. "hash" is the MD5 digest of the data. "prefix" is the ASN.1 BER MD5 algorithm designator prefix required in PKCS #1 , that is, This prefix is included to make it easier to use standard cryptographic libraries. The FF octet MUST be repeated enough times that the value of the quantity being CRYPTed is exactly one octet shorter than the RSA modulus. See for MD5 security considerations.

RSA-SHA256 This implies the PKCS #1 v1.5 padding algorithm as described in but with the ASN.1 BER SHA-256 algorithm designator prefix. An example of use is: ]]>

RSA-SHA384 This implies the PKCS #1 v1.5 padding algorithm as described in but with the ASN.1 BER SHA-384 algorithm designator prefix. An example of use is: ]]> Because it takes about the same effort to calculate a SHA-384 message digest as it does a SHA-512 message digest, it is suggested that RSA- SHA512 be used in preference to RSA-SHA384 where possible.

RSA-SHA512 This implies the PKCS #1 v1.5 padding algorithm as described in but with the ASN.1 BER SHA-512 algorithm designator prefix. An example of use is: ]]>

RSA-RIPEMD160 This implies the PKCS #1 v1.5 padding algorithm as described in but with the ASN.1 BER RIPEMD160 algorithm designator prefix. An example of use is: ]]>

ECDSA-SHA*, ECDSA-RIPEMD160, ECDSA-Whirlpool The Elliptic Curve Digital Signature Algorithm (ECDSA) is the elliptic curve analogue of the Digital Signature Algorithm (DSA) signature method, i.e., the Digital Signature Standard (DSS). It takes no explicit parameters. For some detailed specifications of how to use it with SHA hash functions and XML Digital Signature, please see and . The #sha3-*, #ecdsa-ripemd160, and #ecdsa-whirlpool fragments identify signature methods processed in the same way as specified by the #ecdsa-sha1 fragment, with the exception that a SHA3 function (see ), RIPEMD160, or Whirlpool (see ) is used instead of SHA-1. The output of the ECDSA algorithm consists of a pair of integers usually referred to as the pair (r, s). The signature value consists of the base64 encoding of the concatenation of two octet streams that respectively result from the octet encoding of the values r and s in that order. Conversion from integer to octet stream must be done according to the I2OSP operation defined in the specification with the l parameter equal to the size of the base point order of the curve in octets (e.g., 32 for the P-256 curve and 66 for the P-521 curve ). For an introduction to elliptic curve cryptographic algorithms, see and note the errata (Errata IDs 2773-2777).

ESIGN-SHA* The ESIGN algorithm specified in is a signature scheme based on the integer factorization problem. An example of use is: ]]>

RSA-Whirlpool As in the definition of the RSA-SHA1 algorithm in , the designator "RSA" means the RSASSA-PKCS1-v1_5 algorithm as defined in . When identified through the #rsa-whirlpool fragment identifier, Whirlpool is used as the hash algorithm instead. Use of the ASN.1 BER Whirlpool algorithm designator is implied. That designator is: as an explicit octet sequence. This corresponds to OID 1.0.10118.3.0.55 defined in . An example of use is: ]]>

RSASSA-PSS with Parameters These identifiers use the PKCS #1 EMSA-PSS encoding algorithm . The RSASSA-PSS algorithm takes the digest method (hash function), a mask generation function, the salt length in octets (SaltLength), and the trailer field as explicit parameters. Algorithm identifiers for hash functions specified in XML encryption , , and in are considered to be valid algorithm identifiers for hash functions. According to , the default value for the digest function is SHA-1, but due to the discovered weakness of SHA-1 , it is recommended that SHA-256 or a stronger hash function be used. Notwithstanding , SHA-256 is the default to be used with these SignatureMethod identifiers if no hash function has been specified. The default salt length for these SignatureMethod identifiers, if the SaltLength is not specified, SHALL be the number of octets in the hash value of the digest method as recommended in . In a parameterized RSASSA-PSS signature, the ds:DigestMethod and the SaltLength parameters usually appear. If they do not, the defaults make this equivalent to (see ). The TrailerField defaults to 1 (0xBC) when omitted. Schema Definition (target namespace ): Top level element that can be used in xs:any namespace="#other" wildcard of ds:SignatureMethod content. ]]>

RSASSA-PSS without Parameters currently specifies only one mask generation function MGF1 based on a hash function. Although allows for parameterization, the default is to use the same hash function as the digest method function. Only this default approach is supported by this section; therefore, the definition of a mask generation function type is not needed yet. The same applies to the trailer field. There is only one value (0xBC) specified in . Hence, this default parameter must be used for signature generation. The default salt length is the length of the hash function. An example of use is: ]]>

RSA-SHA224 This implies the PKCS #1 v1.5 padding algorithm as described in but with the ASN.1 BER SHA-224 algorithm designator prefix. An example of use is: ]]> Because it takes about the same effort to calculate a SHA-224 message digest as it does a SHA-256 message digest, it is suggested that RSA-SHA256 be used in preference to RSA-SHA224 where possible. See also concerning an erroneous version of this URI that appeared in RFC 6931.

Edwards-Curve The Edwards-curve Digital Signature Algorithm (EdDSA) is a variant of Schnorr's signature system with Edwards curves. A specification is provided and some advantages listed in . The general EdDSA takes 11 parameters that must be carefully chosen for secure and efficient operation. Identifiers for two variants, Ed25519 and Ed448, are given below. Ed25519 uses 32-octet public keys and produces 64-octet signatures. It provides about 128 bits of security and uses SHA-512 internally as part of signature generation. Ed448 uses 57-octet public keys and produces 114-octet signatures. It provides about 224 bits of security and uses "SHAKE256" internally as part of signature generation. (SHAKE256 is specified by NIST as an "Extensible Output Function" and not specified or approved by NIST as a secure hash function.) For further information on the variants of EdDSA identified below, see . An example of use is: ]]>

Minimal Canonicalization Thus far, two independent interoperable implementations of Minimal Canonicalization have not been announced. Therefore, when "XML-Signature Syntax and Processing" was advanced along the Standards Track from to , Minimal Canonicalization was dropped. However, there was still interest. For its definition, see .

Transform Algorithms The XPointer Transform algorithm syntax is described below. All CanonicalizationMethod algorithms can also be used as Transform algorithms.

XPointer This transform algorithm takes an as an explicit parameter. An example of use is: xpointer(id("foo")) xmlns(bar=http://foobar.example) xpointer(//bar:Zab[@Id="foo"]) Schema Definition: DTD: ]]> Input to this transform is an octet stream (which is then parsed into XML). Output from this transform is a node set; the results of the XPointer are processed as defined in the XMLDSIG specification for a same-document XPointer.

EncryptionMethod Algorithms This subsection gives identifiers and information for several EncryptionMethod Algorithms.

ARCFOUR Encryption Algorithm ARCFOUR is a fast, simple stream encryption algorithm that is compatible with RSA Security's RC4 algorithm (Rivest Cipher 4); however, RC4 has been found to have a number of weaknesses and its use is prohibited in several IETF protocols, for example TLS . An example EncryptionMethod element using ARCFOUR is: 40 ]]> ARCFOUR makes use of the generic KeySize parameter specified and defined in .

Camellia Block Encryption Camellia is a block cipher with the same interface as the AES ; it has a 128-bit block size and 128-, 192-, and 256-bit key sizes. In XML Encryption, Camellia is used in the same way as the AES: It is used in the Cipher Block Chaining (CBC) mode with a 128-bit initialization vector (IV). The resulting cipher text is prefixed by the IV. If included in XML output, it is then base64 encoded. An example Camellia EncryptionMethod is as follows: ]]>

Camellia Key Wrap Camellia key wrap is identical to the AES key wrap algorithm specified in the XML Encryption standard with "AES" replaced by "Camellia". As with AES key wrap, the check value is 0xA6A6A6A6A6A6A6A6. The algorithm is the same regardless of the size of the Camellia key used in wrapping, called the "key encrypting key" or "KEK". If Camellia is supported, it is particularly suggested that wrapping 128-bit keys with a 128-bit KEK and wrapping 256-bit keys with a 256-bit KEK be supported. An example of use is: ]]>

PSEC-KEM, RSAES-KEM, and ECIES-KEM These algorithms, specified in , are key encapsulation mechanisms using elliptic curve or RSA encryption. RSAEA-KEM and ECIES-KEM are also specified in . An example of use of PSEC-KEM is: version id curve base order cofactor ]]> See for information on the parameters above.

SEED Block Encryption SEED is a block cipher with a 128-bit block size and 128-bit key size. In XML Encryption, SEED can be used in the Cipher Block Chaining (CBC) mode with a 128-bit initialization vector (IV). The resulting cipher text is prefixed by the IV. If included in XML output, it is then base64 encoded. An example SEED EncryptionMethod is as follows: ]]>

SEED Key Wrap Key wrapping with SEED is identical to with "AES" replaced by "SEED". The algorithm is specified in . The implementation of SEED is optional. The default initial value is 0xA6A6A6A6A6A6A6A6. An example of use is: ]]>

ChaCha20 ChaCha20 , a stream cipher, is a variant of Salsa20 . It is considerably faster than AES in software-only implementations. In addition to a 256-bit key and the plain text to be encrypted, ChaCha20 takes a 96-bit Nonce and an initial 32-bit Counter. The Nonce and Counter are represented as hex in nested elements as shown below. An example of use is: 0123456789abcdef01234567 fedcba09 ]]>

ChaCha20+Poly1305 ChaCha20+Poly1305 is an Authenticated Encryption with Associated Data (AEAD) algorithm. In addition to a 256-bit key and plain text to be encrypted and authenticated, ChaCha20+Poly1305 takes a 96-bit Nonce and variable-length Additional Authenticated Data (AAD). The Nonce is represented as a child element of the EncryptionMethod element with a hex value. The AAD is a string, which may be null. The AAD element may be absent, in which case the AAD is null. The CipherData, either present in the CipherValue or by reference, is the concatenation of the encrypted ChaCha20 output and the Poly1305 128-bit tag. An example of use is: 0123456789abcdef01234567 The quick brown fox jumps over the lazy dog. ]]>

Key AgreementMethod Algorithm This subsection gives identifiers and information for an additional key AgreementMethod Algorithm .

X25519 and X448 Key Agreement The X25519 and X448 key agreement algorithms are specified in .

KeyDerivationMethod Algorithm This subsection gives identifiers and information for an additional KeyDerivationMethod Algorithm .

HKDF Key Derivation This section covers the HMAC-based Extract-and-Expand Key Derivation Function (HKDF ). HKDF takes as inputs a hash function, an optional non-secret "salt", initial keying material (IKM), optional context and application-specific "info", and the required output keying size. Note that these strictly determine the output so, for example, invoking HKDF at different times but with the same salt, info, initial keying material, and output key size will produce identical output keying material. The inputs can be supplied to HKDF as follows:

hash function:

The algorithm attribute of a child DigestMethod element.

salt:

The content of a Salt child element of AgreementMethod in hex. If not provided, a string of zero octets as long as the hash function output is used as specified in .

IKM:

The content of an OriginatorKeyInfo child element of AgreementMethod in hex. May be absent in some applications where this is known through some other method.

info:

The content of the KA-Nonce child element of AgreementMethod in hex.

size:

The content of a KeySize child element of AgreementMethod as a decimal number.

Here is the test case from as an example: 000102030405060708090a0b0c 0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b f0f1f2f3f4f5f6f7f8f9 42 ]]>

KeyInfo In , a KeyInfo element child is specified, while in , additional KeyInfo Type values for use in RetrievalMethod are specified.

PKCS #7 Bag of Certificates and CRLs A PKCS #7 "signedData" can also be used as a bag of certificates and/or certificate revocation lists (CRLs). The PKCS7signedData element is defined to accommodate such structures within KeyInfo. The binary PKCS #7 structure is base64 encoded. Any signer information present is ignored. The following is an example , eliding the base64 data: ... ]]>

Additional RetrievalMethod Type Values The Type attribute of RetrievalMethod is an optional identifier for the type of data to be retrieved. The result of dereferencing a RetrievalMethod reference for all KeyInfo types with an XML structure is an XML element or document with that element as the root. The various "raw" key information types return a binary value. Thus, they require a Type attribute because they are not unambiguously parsable.

Indexes The following subsections provide an index by URI and by fragment identifier (the portion of the URI after "#") of the algorithm and KeyInfo URIs defined in this document and in the standards plus the one KeyInfo child element name defined in this document. The "Sec/Doc" column has the section of this document or, if not specified in this document, the standards document where the item is specified. See also .

Index by Fragment Index The initial "http://www.w3.org/" part of the URI is not included below. The first six entries have a null fragment identifier or no fragment identifier. "{Bad}" indicates a bad value that was accidentally included in RFC 6931. Implementations SHOULD only generate the correct URI but SHOULD understand both the correct and erroneous URI. See also . The initial "http://www.w3.org/" part of the URI is not included above.

Index by URI The initial "http://www.w3.org/" part of the URI is not included below. "{Bad}" indicates a Bad value that was accidentally included in RFC 6931. Implementations SHOULD only generate the correct URI but SHOULD understand both the correct and erroneous URI. See also . The initial "http://www.w3.org/" part of the URI is not included above. "{Bad}" indicates a Bad value that was accidentally included in RFC 6931. Implementations SHOULD only generate the correct URI but SHOULD understand both the correct and erroneous URI. See also .

Allocation Considerations W3C and IANA allocation considerations are given below.

W3C Allocation Considerations As it is easy for people to construct their own unique URIs and, if appropriate, to obtain a URI from the W3C, additional URI specification under the following XMLSEC URI prefixes is prohibited as shown:

URI	Status
	Frozen by W3C.
	Frozen with RFC 4051.
	Frozen with RFC 6931.

The W3C has assigned for additional new URIs specified in this document. There are also occurrences in this document of due to the inclusion of some algorithms from for convenience. An "xmldsig-more" URI does not imply any official W3C or IETF status for these algorithms or identifiers nor does it imply that they are only useful in digital signatures. Currently, dereferencing such URIs may or may not produce a temporary placeholder document. Permission to use these URI prefixes has been given by the W3C.

IANA Considerations IANA has established a registry entitled "XML Security URIs". IANA is requested to update its contents to correspond to of this document with each section number in the "Sec/Doc" column augmented with a reference to this RFC (for example, "2.6.4" means "[this document], Section 2.6.4"). IANA is requested to update all references to in that registry to [this document]. New entries, including new Types, will be added based on Specification Required . Criteria for the designated expert for inclusion are (1) documentation sufficient for interoperability of the algorithm or data type and the XML syntax for its representation and use and (2) sufficient importance as normally indicated by inclusion in (2a) an approved W3C Note, Proposed Recommendation, or Recommendation, or (2b) an approved RFC. Typically, the registry will reference a W3C or IETF document specifying such XML syntax; that document will either contain a more detailed description of the algorithm or data type or reference another document with a more detailed description.

Security Considerations This RFC is concerned with documenting the URIs that designate algorithms and some data types used in connection with XML security. The security considerations vary widely with the particular algorithms, and the general security considerations for XML security are outside of the scope of this document but appear in , , , , and . should be consulted before considering the use of MD5 as a DigestMethod or the use of HMAC-MD5 or RSA-MD5 as a SignatureMethod. See for SHA-1 security considerations. Additional security considerations are given in connection with the description of some algorithms in the body of this document. Implementers should be aware that cryptographic algorithms become weaker with time. As new cryptoanalysis techniques are developed and computing performance improves, the work factor to break a particular cryptographic algorithm will decrease. Therefore, cryptographic implementations should be modular, allowing new algorithms to be readily inserted. That is, implementers should be prepared for the set of mandatory-to-implement algorithms for any particular use to change over time. This is sometimes referred to as "algorithm agility" .

Normative References ISO ISO National Institute of Standards and Technology (NIST) National Institute of Standards and Technology (NIST) National Institute of Standards and Technology (NIST) Institute of Electrical and Electronics Engineers National Institute of Standards and Technology (NIST) American National Standards Institute, Accredited Standards Committee X9 Informative References ITU-T ITU-T In Selected Areas in Cryptography 7th Annual International Workshop SAC 2000 RFC Errata RFC 6931 RFC Errata RFC 6931 RFC Errata RFC 6931 Version 2.1 Department of Computer Science, University of Illinois at Chicago W3C Recommendation W3C Recommendation W3C Proposed Recommendation W3C Recommendation W3C Working Group Note IANA W3C Recommendation Second Edition

Changes from RFC 9231 The following changes have been made in to produce this document.

• Deleted Appendix on Changes from RFC 6931, since they were already included in , and remove reference to RFC 6931 and to the Errata against RFC 6931.
• Corrected URIs as follows: OLD => CORRECTED 2001/06/xml-exc-c14n# => 2001/10/xml-exc-c14n# 2001/06/xml-exc-c14n#WithComments => 2001/10/xml-exc-c14n#WithComments 2006/12/xmlc14n11# => 2006/12/xml-c14n11$ 2006/12/xmlc14n11#WithComments => 2006/12/xml-c14n11#WithComments
• Added the following algorithms:

Section	Algorithm(s)
tbd	tbd

• Fixed minor typos and added editorial changes.

Bad URIs RFC 6931 included two bad URIs as shown below. "{Bad}" in the indexes (Sections and ) indicates such a bad value. Implementations SHOULD only generate the correct URI but SHOULD understand both the correct and erroneous URI. 2006/12/xmlc12n11#

• Appears in the indices (Sections 4.1 and 4.2) of RFC 6931 when it should be "2006/12/xml-c14n11#" (i.e., the "12" inside "xmlc12n11" should have been "14"). This is and in addition there should be a hyphen after "xml". These errors are corrected in this document.

2007/05/xmldsig-more#rsa-sha224

• Appears in the indices (Sections 4.1 and 4.2) of RFC 6931 when it should be "2001/04/xmldsig-more#rsa-sha224". This is and is corrected in this document.

Acknowledgements The contributions of the following, listed in alphabetic order, by contributing to this document, are gratefully acknowledged: Andrey Kislyuk The contributions of the following, listed in alphabetic order, by reporting errata against RFC 6931 or contributing to this document, are gratefully acknowledged: , , , , , , , , , and . The contributions of the following, listed in alphabetic order, to RFC 6931, on which this document is based, are gratefully acknowledged: , , , , , , , , , , , , , , , , , and . The following contributors to RFC 4051 are gratefully acknowledged: , , , , , , , and .