RFC4051 - Additional XML Security Uniform Resource Identifiers (URIs)

Network Working Group D. Eastlake 3rd

Request for Comments: 4051 Motorola Laboratories

Category: Standards Track April 2005

Additional XML Security Uniform Resource Identifiers (URIs)

Status of This Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Abstract

A number of Uniform Resource Identifiers (URIs) intended for use with

XML Digital Signatures, Encryption, and Canonicalization are defined.

These URIs identify algorithms and types of keying information.

Table of Contents

1. IntrodUCtion.................................................. 2

2. Algorithms.................................................... 3

2.1. DigestMethod Algorithms................................. 3

2.1.1. MD5............................................. 3

2.1.2. SHA-224......................................... 3

2.1.3. SHA-384......................................... 4

2.2. SignatureMethod Message Authentication Code Algorithms.. 4

2.2.1. HMAC-MD5........................................ 4

2.2.2. HMAC SHA Variations............................. 5

2.2.3. HMAC-RIPEMD160.................................. 6

2.3. SignatureMethod Public Key Signature Algorithms......... 6

2.3.1. RSA-MD5......................................... 6

2.3.2. RSA-SHA256...................................... 7

2.3.3. RSA-SHA384...................................... 7

2.3.4. RSA-SHA512...................................... 7

2.3.5. RSA-RIPEMD160................................... 8

2.3.6. ECDSA-SHA*...................................... 8

2.3.7. ESIGN-SHA1...................................... 8

2.4. Minimal Canonicalization................................ 9

2.5. Transform Algorithms.................................... 9

2.5.1. XPointer........................................ 9

2.6. EncryptionMethod Algorithms............................. 10

2.6.1. ARCFOUR Encryption Algorithm.................... 10

2.6.2. Camellia Block Encryption....................... 10

2.6.3. Camellia Key Wrap............................... 11

2.6.4. PSEC-KEM........................................ 11

3. KeyInfo....................................................... 12

3.1. PKCS #7 Bag of Certificates and CRLs.................... 12

3.2. Additional RetrievalMethod Type Values.................. 12

4. IANA Considerations........................................... 13

5. Security Considerations....................................... 13

Acknowledgements.................................................. 13

Normative References.............................................. 13

Informative References............................................ 15

Author's Address.................................................. 16

Full Copyright Statement.......................................... 17

1. Introduction

XML Digital Signatures, Canonicalization, and Encryption have been

standardized by the W3C and the joint IETF/W3C XMLDSIG working group.

All of these are now W3C Recommendations and IETF Informational or

Standards Track documents. They are available as follows:

IETF level W3C REC Topic

----------- ------- -----

[RFC3275] Draft Std [XMLDSIG] XML Digital Signatures

[RFC3076] Info [CANON] Canonical XML

- - - - - - [XMLENC] XML Encryption

[RFC3741] Info [EXCANON] Exclusive XML Canonicalization

All of these standards and recommendations use URIs [RFC2396] to

identify algorithms and keying information types. This document

provides a convenient reference list of URIs and descriptions for

algorithms in which there is substantial interest, but which cannot

or have not been included in the main documents. Note that raising

XML digital signature to a Draft Standard in the IETF required

removal of any algorithms for which interoperability from the main

standards document has not been demonstrated. This required removal

of the Minimal Canonicalization algorithm, in which there appears to

be a continued interest, to be dropped from the standards track

specification. It is included here.

The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

document are to be interpreted as described in [RFC2119].

2. Algorithms

The URI [RFC2396] being dropped from the standard because of the

transition from Proposed Standard to Draft Standard is included in

Section 2.4 with its original prefix so as to avoid changing the

XMLDSIG standard's namespace.

http://www.w3.org/2000/09/xmldsig#

Additional algorithms are given URIs that start with:

http://www.w3.org/2001/04/xmldsig-more#

An "xmldsig-more" URI does not imply any official W3C status for

these algorithms or identifiers or that they are only useful in

digital signatures. Currently, dereferencing such URIs may or may

not produce a temporary placeholder document. Permission to use this

URI prefix has been given by the W3C.

2.1. DigestMethod Algorithms

These algorithms are usable wherever a DigestMethod element occurs.

2.1.1. MD5

Identifier:

http://www.w3.org/2001/04/xmldsig-more#md5

The MD5 algorithm [RFC1321] 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 [RFC2405] encoding of this bit string

viewed as a 16-octet octet stream.

2.1.2. SHA-224

Identifier:

http://www.w3.org/2001/04/xmldsig-more#sha224

The SHA-224 algorithm [FIPS-180-2change, RFC3874] 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 [RFC2405] encoding of this string viewed

as a 28-octet stream. Because it takes roughly the same amount of

effort to compute a SHA-224 message digest as a SHA-256 digest, and

terseness is usually not a criteria in an XML application,

consideration should be given to the use of SHA-256 as an

alternative.

2.1.3. SHA-384

Identifier:

http://www.w3.org/2001/04/xmldsig-more#sha384

The SHA-384 algorithm [FIPS-180-2] 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 [RFC2405] encoding of this string viewed

as a 48-octet stream. Because it takes roughly the same amount of

effort to compute a SHA-384 message digest as a SHA-512 digest and

terseness is usually not a criteria in XML application, consideration

should be given to the use of SHA-512 as an alternative.

2.2. SignatureMethod Message Authentication Code Algorithms

Note: Some text in this section is duplicated from [RFC3275] for the

convenience of the reader. RFC 3275 is normative in case of

conflict.

2.2.1. HMAC-MD5

Identifier:

http://www.w3.org/2001/04/xmldsig-more#hmac-md5

The HMAC algorithm [RFC2104] 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 ultimately the output (possibly

truncated) of the chosen digest algorithm. This value shall be

base64 [RFC2405] encoded in the same straightforward fashion as the

output of the digest algorithms. For example, the SignatureValue

element for the HMAC-MD5 digest

9294727A 3638BB1C 13F48EF8 158BFC9D

from the test vectors in [RFC2104] would be

kpRyejY4uxwT9I74FYv8nQ==

Schema Definition:

DTD:

The Schema Definition and DTD immediately shown above are taken from

[RFC3275].

Although some cryptographic suspicions have recently been cast on MD5

for use in signatures such as RSA-MD5 below, this does not effect use

of MD5 in HMAC.

2.2.2. HMAC SHA Variations

Identifiers:

http://www.w3.org/2001/04/xmldsig-more#hmac-sha224

http://www.w3.org/2001/04/xmldsig-more#hmac-sha256

http://www.w3.org/2001/04/xmldsig-more#hmac-sha384

http://www.w3.org/2001/04/xmldsig-more#hmac-sha512

SHA-224, SHA-256, SHA-384, and SHA-512 [FIPS-180-2, FIPS-180-2change,

RFC3874] can also be used in HMAC as described in section 2.2.1 for

HMAC-MD5.

2.2.3. HMAC-RIPEMD160

Identifier:

http://www.w3.org/2001/04/xmldsig-more#hmac-ripemd160

RIPEMD-160 [RIPEMD-160] can also be used in HMAC as described in

section 2.2.1 for HMAC-MD5.

2.3. SignatureMethod Public Key Signature Algorithms

These algorithms are distinguished from those in Section 2.2 in that

they use public key methods. The verification key is different from

and not feasibly derivable from the signing key.

2.3.1. RSA-MD5

Identifier:

http://www.w3.org/2001/04/xmldsig-more#rsa-md5

RSA-MD5 implies the PKCS#1 v1.5 padding algorithm described in

[RFC3447]. An example of use is

The SignatureValue content for an RSA-MD5 signature is the base64

[RFC2405] encoding of the octet string computed as per [RFC3447],

section 8.1.1, signature generation for the RSASSA-PKCS1-v1_5

signature scheme. As specified in the EMSA-PKCS1-V1_5-ENCODE

function in [RFC3447, section 9.2.1], the value input to the

signature function MUST contain a pre-pended algorithm object

identifier for the hash function, but the availability of an ASN.1

parser and recognition of OIDs are not required of a signature

verifier. The PKCS#1 v1.5 representation appears as:

CRYPT (PAD (ASN.1 (OID, DIGEST (data))))

Note that the padded ASN.1 will be of the following form:

01 FF* 00 prefix hash

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 [RFC3447], that is:

hex 30 20 30 0c 06 08 2a 86 48 86 f7 0d 02 05 05 00 04 10

This prefix is included to facilitate the use of 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.

Due to increases in computer processor power and advances in

cryptography, use of RSA-MD5 is NOT RECOMMENDED.

2.3.2. RSA-SHA256

Identifier:

http://www.w3.org/2001/04/xmldsig-more#rsa-sha256

This implies the PKCS#1 v1.5 padding algorithm [RFC3447] as described

in section 2.3.1, but with the ASN.1 BER SHA-256 algorithm designator

prefix. An example of use is:

2.3.3 RSA-SHA384

Identifier:

http://www.w3.org/2001/04/xmldsig-more#rsa-sha384

This implies the PKCS#1 v1.5 padding algorithm [RFC3447] as described

in section 2.3.1, 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 a SHA-512 message digest, it is suggested that RSA-SHA512

be used in preference to RSA-SHA384 where possible.

2.3.4. RSA-SHA512

Identifier:

http://www.w3.org/2001/04/xmldsig-more#rsa-sha512

This implies the PKCS#1 v1.5 padding algorithm [RFC3447] as described

in section 2.3.1, but with the ASN.1 BER SHA-512 algorithm designator

prefix. An example of use is:

2.3.5. RSA-RIPEMD160

Identifier:

http://www.w3.org/2001/04/xmldsig-more/rsa-ripemd160

This implies the PKCS#1 v1.5 padding algorithm [RFC3447], as

described in section 2.3.1, but with the ASN.1 BER RIPEMD160

algorithm designator prefix. An example of use is:

2.3.6. ECDSA-SHA*

Identifiers

http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha1

http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha224

http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha256

http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha384

http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha512

The Elliptic Curve Digital Signature Algorithm (ECDSA) [FIPS-186-2]

is the elliptic curve analogue of the DSA (DSS) signature method.

For detailed specifications on how to use it with SHA hash functions

and XML Digital Signature, please see [X9.62] and [ECDSA].

2.3.7. ESIGN-SHA1

Identifier

http://www.w3.org/2001/04/xmldsig-more#esign-sha1

http://www.w3.org/2001/04/xmldsig-more#esign-sha224

http://www.w3.org/2001/04/xmldsig-more#esign-sha256

http://www.w3.org/2001/04/xmldsig-more#esign-sha384

http://www.w3.org/2001/04/xmldsig-more#esign-sha512

The ESIGN algorithm specified in [IEEE-P1363a] is a signature scheme

based on the integer factorization problem. It is much faster than

previous digital signature schemes so ESIGN can be implemented on

smart cards without special co-processors.

An example of use is:

2.4. Minimal Canonicalization

Thus far two independent interoperable implementations of Minimal

Canonicalization have not been announced. Therefore, when XML

Digital Signature was advanced from Proposed Standard [RFC3075] to

Draft Standard [RFC3275], Minimal Canonicalization was dropped from

the standards track documents. However, there is still interest in

Minimal Canonicalization, indicating its possible future use. For

its definition, see [RFC3075], Section 6.5.1.

For reference, its identifier remains:

http://www.w3.org/2000/09/xmldsig#minimal

2.5. Transform Algorithms

Note that all CanonicalizationMethod algorithms can also be used as

transform algorithms.

2.5.1. XPointer

Identifier:

http://www.w3.org/2001/04/xmldsig-more/xptr

This transform algorithm takes an [XPointer] as an explicit

parameter. An example of use is [RFC3092]:

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 [RFC3275] for a

same document XPointer.

2.6. EncryptionMethod Algorithms

This subsection gives identifiers and information for several

EncryptionMethod Algorithms.

2.6.1. ARCFOUR Encryption Algorithm

Identifier:

http://www.w3.org/2001/04/xmldsig-more#arcfour

ARCFOUR is a fast, simple stream encryption algorithm that is

compatible with RSA Security's RC4 algorithm. An example of the

EncryptionMethod element using ARCFOUR is

Note that Arcfour makes use of the generic KeySize parameter

specified and defined in [XMLENC].

2.6.2. Camellia Block Encryption

Identifiers:

http://www.w3.org/2001/04/xmldsig-more#camellia128-cbc

http://www.w3.org/2001/04/xmldsig-more#camellia192-cbc

http://www.w3.org/2001/04/xmldsig-more#camellia256-cbc

Camellia is an efficient and secure block cipher with the same

interface as the AES [Camellia, RFC3713], that is 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:

2.6.3. Camellia Key Wrap

Identifiers:

http://www.w3.org/2001/04/xmldsig-more#kw-camellia128

http://www.w3.org/2001/04/xmldsig-more#kw-camellia192

http://www.w3.org/2001/04/xmldsig-more#kw-camellia256

The Camellia [Camellia, RFC3713] key wrap is identical to the AES key

wrap algorithm [RFC3394] 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). The

implementation of Camellia is OPTIONAL. However, if it is supported,

the same implementation guidelines of which combinations of KEK size

and wrapped key size should be required to be supported and which are

optional to be supported should be followed as for AES. That is to

say, if Camellia key wrap is supported, then wrapping 128-bit keys

with a 128-bit KEK and wrapping 256-bit keys with a 256-bit KEK are

REQUIRED and all other combinations are OPTIONAL.

An example of use is:

2.6.4. PSEC-KEM

Identifier:

http://www.w3.org/2001/04/xmldsig-more#psec-kem

The PSEC-KEM algorithm, specified in [ISO/IEC-18033-2], is a key

encapsulation mechanism using elliptic curve encryption.

An example of use is:

version

curve

base

order

cofactor

See [ISO/IEC-18033-2] for information on the parameters above.

3. KeyInfo

In section 3.1 a new KeyInfo element child is specified, while in

section 3.2 additional KeyInfo Type values for use in RetrievalMethod

are specified.

3.1. PKCS #7 Bag of Certificates and CRLs

A PKCS #7 [RFC2315] "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 [RFC2405]

encoded. Any signer information present is ignored. The following

is an example, eliding the base64 data [RFC3092]:

...

3.2. 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

parseable.

Identifiers:

http://www.w3.org/2001/04/xmldsig-more#KeyValue

http://www.w3.org/2001/04/xmldsig-more#RetrievalMethod

http://www.w3.org/2001/04/xmldsig-more#KeyName

http://www.w3.org/2001/04/xmldsig-more#rawX509CRL

http://www.w3.org/2001/04/xmldsig-more#rawPGPKeyPacket

http://www.w3.org/2001/04/xmldsig-more#rawSPKISexp

http://www.w3.org/2001/04/xmldsig-more#PKCS7signedData

http://www.w3.org/2001/04/xmldsig-more#rawPKCS7signedData

4. IANA Considerations

As it is easy for people to construct their own unique URIs [RFC2396]

and possibly oBTain a URI from the W3C if appropriate, it is not

intended that any additional "http://www.w3.org/2001/04/xmldsig-

more#" URIs be created beyond those enumerated in this document.

(W3C Namespace stability rules prohibit the creation of new URIs

under "http://www.w3.org/2000/09/xmldsig#".)

5. Security Considerations

Due to computer speed and cryptographic advances, the use of MD5 as a

DigestMethod and the use of MD5 in the RSA-MD5 SignatureMethod is NOT

RECOMMENDED. The concerned cryptographic advances do not effect the

security of HMAC-MD5; however, there is little reason not to use one

of the SHA series of algorithms.

Acknowledgements

Glenn Adams, Merlin Hughs, Gregor Karlinger, Brian LaMachia, Shiho

Moriai, Joseph Reagle, Russ Housley, and Joel Halpern.

Normative References

[Camellia] "Camellia: A 128-bit Block Cipher Suitable for

Multiple Platforms - Design and Analysis -", K.

Aoki, T. Ichikawa, M. Matsui, S. Moriai, J.

Nakajima, T. Tokita, In Selected Areas in

Cryptography, 7th Annual International Workshop,

SAC 2000, August 2000, Proceedings, Lecture Notes

in Computer Science 2012, pp. 39-56, Springer-

Verlag, 2001.

[ECDSA] Blake-Wilson, S., Karlinger, G., Kobayashi, T.,

and Y. Wang, "Using the Elliptic Curve Signature

Algorithm (ECDSA) for XML Digital Signatures", RFC

4050, April 2005.

[FIPS-180-2] "Secure Hash Standard", (SHA-1/256/384/512) US

Federal Information Processing Standard, 1 August

2002.

[FIPS-180-2change] "FIPS 180-2, Secure Hash Standard Change Notice

1", adds SHA-224 to [FIPS 180-2], 25 February

2004.

[FIPS-186-2] "Digital Signature Standard", National Institute

of Standards and Technology, 2000.

[IEEE-P1363a] "Standard Specifications for Public Key

Cryptography: Additional Techniques", October

2002.

[ISO/IEC-18033-2] "Information technology -- Security techniques --

Encryption algorithms -- Part 3: Asymmetric

ciphers", CD, October 2002.

[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm ",

RFC 1321, April 1992.

[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:

Keyed-Hashing for Message Authentication", RFC

2104, February 1997.

[RFC2119] Bradner, S., "Key words for use in RFCs to

Indicate Requirement Levels", BCP 14, RFC 2119,

March 1997.

[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter,

"Uniform Resource Identifiers (URI): Generic

Syntax", RFC 2396, August 1998.

[RFC2405] Madson, C. and N. Doraswamy, "The ESP DES-CBC

Cipher Algorithm With Explicit IV", RFC 2405,

November 1998.

[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message

Syntax Version 1.5", RFC 2315, March 1998.

[RFC3075] Eastlake 3rd, D., Reagle, J., and D. Solo, "XML-

Signature Syntax and Processing", RFC 3075, March

2001. (RFC 3075 was obsoleted by RFC 3275 but is

referenced in this document for its description of

Minimal Canonicalization which was dropped in RFC

3275.)

[RFC3275] Eastlake 3rd, D., Reagle, J., and D. Solo,

"(Extensible Markup Language) XML-Signature Syntax

and Processing", RFC 3275, March 2002.

[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption

Standard (AES) Key Wrap Algorithm", RFC 3394,

September 2002.

[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key

Cryptography Standards (PKCS) #1: RSA Cryptography

Specifications Version 2.1", RFC 3447, February

2003.

[RFC3713] Matsui, M., Nakajima, J., and S. Moriai, "A

Description of the Camellia Encryption Algorithm",

RFC 3713, April 2004.

[RFC3874] Housley, R., "A 224-bit One-way Hash Function:

SHA-224", RFC 3874, September 2004.

[RIPEMD-160] ISO/IEC 10118-3:1998, "Information Technology -

Security techniques - Hash-functions - Part3:

Dedicated hash- functions", ISO, 1998.

[X9.62] X9.62-200X, "Public Key Cryptography for the

Financial Services Industry: The Elliptic Curve

Digital Signature Algorithm (ECDSA)", Accredited

Standards Committee X9, American National

Standards Institute.

[XMLDSIG] "XML-Signature Syntax and Processing", D. Eastlake

3rd, J. Reagle, & D. Solo, 12 February 2002.

[XMLENC] "XML Encryption Syntax and Processing", J. Reagle,

D. Eastlake, December 2002.

[XPointer] "XML Pointer Language (XPointer) Version 1.0", W3C

working draft, Steve DeRose, Eve Maler, Ron Daniel

Jr., January 2001.

Informative References

[CANON] "Canonical XML Version 1.0", John Boyer.

[EXCANON] "Exclusive XML Canonicalization Version 1.0", D.

Eastlake, J. Reagle, 18 July 2002.

[RFC3076] Boyer, J., "Canonical XML Version 1.0", RFC 3076,

March 2001.

[RFC3092] Eastlake 3rd, D., Manros, C., and E. Raymond,

"Etymology of "Foo"", RFC 3092, 2001.

[RFC3741] Boyer, J., Eastlake 3rd, D., and J. Reagle,

"Exclusive XML Canonicalization, Version 1.0", RFC

3741, March 2004.

Author's Address

Donald E. Eastlake 3rd

Motorola Laboratories

155 Beaver Street

Milford, MA 01757 USA

Phone: +1-508-786-7554 (w)

+1-508-634-2066 (h)

EMail: Donald.Eastlake@motorola.com

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