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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Sean Turner, IECA 2 Internet Draft November 9, 2009 3 Intended Status: Standard Track 4 Expires: March 9, 2010 6 Algorithms for Asymmetric Key Package Content Type 7 draft-turner-asymmetrickeyformat-algs-00.txt 9 Status of this Memo 11 This Internet-Draft is submitted to IETF in full conformance with the 12 provisions of BCP 78 and BCP 79. This document may contain material 13 from IETF Documents or IETF Contributions published or made publicly 14 available before November 10, 2008. The person(s) controlling the 15 copyright in some of this material may not have granted the IETF 16 Trust the right to allow modifications of such material outside the 17 IETF Standards Process. Without obtaining an adequate license from 18 the person(s) controlling the copyright in such materials, this 19 document may not be modified outside the IETF Standards Process, and 20 derivative works of it may not be created outside the IETF Standards 21 Process, except to format it for publication as an RFC or to 22 translate it into languages other than English. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF), its areas, and its working groups. Note that 26 other groups may also distribute working documents as Internet- 27 Drafts. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/1id-abstracts.txt 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html 40 This Internet-Draft will expire on November 9, 2009. 42 Copyright Notice 44 Copyright (c) 2009 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents in effect on the date of 49 publication of this document (http://trustee.ietf.org/license-info). 50 Please review these documents carefully, as they describe your rights 51 and restrictions with respect to this document. 53 Abstract 55 This document describes the conventions for using several 56 cryptographic algorithms with the EncryptedPrivateKeyInfo structure, 57 as defined in RFC 5208. It also includes conventions necessary to 58 protect the AsymmetricKeyPackage content type with SignedData, 59 EnvelopedData, EncryptedData, AuthenticatedData, and 60 AuthEnvelopedData. 62 1. Introduction 64 This document describes the conventions for using several 65 cryptographic algorithms with the EncryptedPrivateKeyInfo structure 66 [RFC5208]. The EncryptedPrivateKeyInfo is used by [P12] to encrypt 67 PrivateKeyInfo [RFCTBD1]. It is similar to EncryptedData [RFC3852] in 68 that it has no recipients, no originators, and no content encryption 69 keys and requires keys be managed by other means. 71 This document also includes conventions necessary to protect the 72 AsymmetricKeyPackage content type [RFCTBD1] with Cryptographic 73 Message Syntax (CMS) protecting content types: SignedData [RFC3852], 74 EnvelopedData [RFC3852], EncryptedData [RFC3852], AuthenticatedData 75 [RFC3852], and AuthEnvelopedData [RFC5083]. Implementations of 76 AsymmetricKeyPackage do not require support for any CMS protecting 77 content type; however, if the AsymmetricKeyPackage is CMS protected 78 it is RECOMMENDED that conventions defined herein be followed. 80 This document does not define any new algorithms instead it refers to 81 previously defined algorithms. 83 1.1. Terminology 85 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 86 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 87 document are to be interpreted as described in [RFC2119]. 89 2. EncryptedPrivateKeyInfo 91 The de facto standard used to encrypt the PrivateKeyInfo structure, 92 which is subsequently placed in the EncryptedPrivateKeyInfo 93 encryptedData field, is Password Based Encryption (PBE) based on 94 PKCS#5 [RFC2898] and PKCS#12 [P12]. The major difference between PKCS 95 #5 and PKCS #12 being the supported encoding for the password: ASCII 96 for PKCS #5 and Unicode for PKCS #12. [RFC2898] specifies two 97 mechanisms PBE Schemes (PBES) 1 and 2, the defacto is PBES 1. The 98 notation for the PBES 1 is: PBEWithAnd. The 99 following schemes are defined in PKCS #5: PBEWithMD2AndDES-CBC, 100 PBEWithMD2AndRC2, PBEWithMD5AndDES-CBC, PBEWithMD5AndRC2, 101 PBEWithSHA1AndDES-CBC, PBEWithSHA1AndRC2. The following schemes are 102 defined in PKCS #12: PBEWithSHAAnd3-KeyTripleDES-CBC, PBEWithSHAAnd2- 103 KeyTripleDES-CBC, PBEWithSHAAnd128BitRC2-CBC, PBEWithSHAAnd40BitRC2- 104 CBC, PBEWithSHAAnd128BitRC4, and PBEWithSHAAnd40BitRC4. 105 Implementation defaults vary. 107 The PBES 1 algorithms require salt and iteration count values. The 108 salt length in PKCS #5 is 8-octets while there is no restriction on 109 the length of the salt in PKCS #12, but PKCS #12 recommends the salt 110 be as long as the digest algorithms output (e.g., 20-octets for SHA- 111 1). The iteration count in PKCS #5 is recommended to be at least 112 1000 and PKCS #12 recommends at least 1024. 114 It is RECOMMENDED that implementations support AES-128 Key Wrap with 115 Padding [RFC5649] or AES-256 Key Wrap with Padding [RFC5649]. 117 3. AsymmetricKeyPackage 119 As noted in Asymmetric Key Packages [RFCTBD1], CMS can be used to 120 protect the AsymmetricKeyPackage. The following provides guidance 121 for SignedData [RFC3852], EnvelopedData [RFC3852], EncryptedData 122 [RFC3852], AuthenticatedData [RFC3852], and AuthEnvelopedData 123 [RFC5083]. 125 3.1. SignedData 127 If an implementation supports SignedData, then it MUST support RSA 128 [RFC3370], SHOULD support RSASSA-PSS [RFC4056], and SHOULD support 129 DSA [RFC3370]. Additionally, implementations MUST support SHA-256 130 [RFCTBD3] and SHOULD support SHA-1 [RFC3370]. 132 3.2. EnvelopedData 134 If an implementation supports EnvelopedData, then it MUST implement 135 the key transport and it MAY implement the key agreement mechanism. 137 When key transport is used, RSA encryption [RFC3370] MUST be 138 supported and RSAES-OAEP [RFC3560] SHOULD be supported. 140 When key agreement is used, Diffie-Hellman ephemeral-static [RFC3370] 141 SHOULD be supported. 143 Regardless of the key management technique choice, implementations 144 MUST support AES-128 Key Wrap with Padding [RFC5649]. 145 Implementations SHOULD support AES-256 Key Wrap with Padding 146 [RFC5649]. 148 When key agreement is used, a key wrap algorithm is also specified to 149 wrap the content encryption key. If the content encryption algorithm 150 is AES-128 Key Wrap with Padding, then key wrap algorithm MUST be 151 AES-128 Key Wrap with Padding [RFC5649]. If the content encryption 152 algorithm is AES-256 Key Wrap with Padding, then the key wrap 153 algorithm MUST be AES-256 Key Wrap with Padding [RFC5649]. 155 3.3. EncryptedData 157 If an implementation supports EncryptedData, then it MUST implement 158 AES-128 Key Wrap with Padding [RFC5649] and MAY implement AES-256 Key 159 Wrap with Padding [RFC5649]. 161 NOTE: EncryptedData requires that keys be managed by means other than 162 EncryptedData; therefore, the only algorithm specified is the content 163 encryption algorithm. 165 3.4. AuthenticatedData 167 If an implementation supports AuthenticatedData, then it MUST 168 implement SHA-256 [RFCTBD3] and SHOULD support SHA-1 [RFC3370] as the 169 message digest algorithm. Additionally, HMAC with SHA-256 [RFC4231] 170 MUST be supported and HMAC with SHA-1 [RFC3370] SHOULD be supported. 172 3.5. AuthEnvelopedData 174 If an implementation supports AuthenticatedData, then it MUST 175 implement the EnvelopedData recommendations except for the content 176 encryption algorithm, which in this case is MUST be either 128-bit 177 AES-CCM or AES-GCM [RFC5084] or SHOULD BE 256-bit AES-CCM or AES-GCM 178 [RFC5084]. 180 4. Public Key Sizes 182 The easiest way to implement the key transport requirement for 183 EnvelopedData and AuthenticatedData is with public key certificates 184 [RFC5280]. If an implementation support RSA, RSAES-OAEP, or DH, then 185 it MUST support key lengths from 1024-bit to 2048-bit, inclusive. 187 5. SMIMECapabilities Attribute 189 [RFCTBD4] defines the SMIMECapabilities attribute as a mechanism for 190 recipients to indicate their supported capabilities including the 191 algorithms they support. The following are values for the 192 SMIMECapabilities attribute for AES Key Wrap with Padding [RFC5649] 193 when used as a content encryption algorithm: 195 AES-128 KW with Padding: 30 0d 06 09 60 86 48 01 65 03 04 01 08 196 AES-192 KW with Padding: 30 0d 06 09 60 86 48 01 65 03 04 01 1C 197 AES-256 KW with Padding: 30 0d 06 09 60 86 48 01 65 03 04 01 30 199 6. Security Considerations 201 The security considerations from [RFC3370], [RFC3394], [RFC3560], 202 [RFC3852], [RFC4056], [RFC4231], [RFC5083], [RFC5084], [RFC5649], 203 [RFCTBD1], and [RFCTBD3] apply. 205 The strength of any encryption scheme is only as good as its weakest 206 link, which in the case of a PBES is the password. Passwords need to 207 provide sufficient entropy to ensure they cannot be easily guessed. 208 The National Institute of Standards and Technology (NIST) Electronic 209 Authentication Guidance [SP800-63] provides some information on 210 password entropy. [SP800-63] indicates that a user chosen 20- 211 character password from a 94-character keyboard with no checks 212 provides 36 bits of entropy. If the 20-character password is 213 randomly chosen, then the amount of entropy is increased to roughly 214 131 bits of entropy. The amount of entropy in the password does not 215 correlate directly to bits of security but in general the more than 216 the better. 218 The choice of content encryption algorithms for this document was 219 based on [RFC5649]: "In the design of some high assurance 220 cryptographic modules, it is desirable to segregate cryptographic 221 keying material from other data. The use of a specific cryptographic 222 mechanism solely for the protection of cryptographic keying material 223 can assist in this goal." Unfortunately, there is no AES-CCM or AES- 224 GCM mode that provides the same properties. If an AES-CCM and AES- 225 GCM mode that provides the same properties is defined, then this 226 document will be updated to adopt that algorithm. 228 [SP800-57] provides comparable bits of security for some algorithms 229 and key sizes. [SP800-57] also provides time frames during which 230 certain numbers of bits of security are appropriate and some 231 environments may find these time frames useful. 233 7. IANA Considerations 235 None. Please remove this section prior to publication as an RFC. 237 8. References 239 8.1. Normative References 241 [P12] RSA Laboratories, "PKCS #12 v1.0: Personal Information 242 Exchange Syntax", June 1999. 244 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 245 Requirement Levels", BCP 14, RFC 2119, March 1997. 247 [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography 248 Specification Version 2.0", RFC 2898, September 2000. 250 [RFC3370] Housley, R., "Cryptographic Message Syntax (CMS) 251 Algorithms", RFC 3370, August 2002. 253 [RFC3394] Housley, R., and J. Schaad, "Advanced Encryption Standard 254 (AES) Key Wrap Algorithm", RFC 3394, September 2002. 256 [RFC3560] Housley, R., "Use of the RSAES-OAEP Key Transport 257 Algorithm in the Cryptographic Message Syntax (CMS)", RFC 258 3560, July 2003. 260 [RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 261 3852, July 2004. 263 [RFC4056] Schaad, J., "Use of RSASSA-PSS Signature Algorithm in 264 Cryptographic Message Syntax (CMS)", RFC 4056, June 2005. 266 [RFC4231] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA- 267 224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC 268 4231, December 2005 270 [RFC5083] Housley, R., "Cryptographic Message Syntax (CMS) 271 Authenticated-Enveloped-Data Content Type", RFC 5083, 272 November 2007. 274 [RFC5084] Housley, R., "Using AES-CCM and AES-GCM Authenticated 275 Encryption in the Cryptographic Message Syntax (CMS)", 276 RFC 5084, November 2007. 278 [RFC5208] Kaliski, B., "Public-Key Cryptography Standards (PKCS) 279 #8: Private-Key Information Syntax Specification Version 280 1.2", RFC 5208, May 2008. 282 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 283 Housley, R., and W. Polk, "Internet X.509 Public Key 284 Infrastructure Certificate and Certificate Revocation 285 List (CRL) Profile", RFC 5280, May 2008. 287 [RFC5649] Housley, R., and M. Dworkin, "Advanced Encryption 288 Standard (AES) Key Wrap with Padding Algorithm", RFC 289 5649, August 2009. 291 [RFCTBD1] Turners, S., "Asymmetric Key Packages", draft-turner- 292 asymmetrickeyformat-02.txt, work-in-progress. 294 [RFCTBD3] Turner, S., "Using SHA2 Algorithms with Cryptographic 295 Message Syntax", draft-ietf-smime-sha2-11.txt, work-in- 296 progress. 298 [RFCTBD4] Turner, S., and B. Ramsdell, "Secure/Multipurpose 299 Internet Mail Extensions (S/MIME) Version 3.2 Message 300 Specification", draft-ietf-smime-3851bis-11.txt, work-in- 301 progress. 303 8.2. Informative References 305 [SP800-57] National Institute of Standards and Technology (NIST), 306 Special Publication 800-57: Recommendation for Key 307 Management - Part 1 (Revised), March 2007. 309 [SP800-63] National Institute of Standards and Technology (NIST), 310 Special Publication 800-63: Electronic Authentication 311 Guidance, April 2006. 313 Authors' Addresses 315 Sean Turner 316 IECA, Inc. 317 3057 Nutley Street, Suite 106 318 Fairfax, VA 22031 319 USA 321 EMail: turners@ieca.com