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'UNICODE' ** Obsolete normative reference: RFC 2279 (ref. 'UTF-8') (Obsoleted by RFC 3629) ** Obsolete normative reference: RFC 2246 (ref. 'TLS') (Obsoleted by RFC 4346) -- Obsolete informational reference (is this intentional?): RFC 2831 (ref. 'DIGEST-MD5') (Obsoleted by RFC 6331) Summary: 9 errors (**), 0 flaws (~~), 4 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT Editor: Kurt D. Zeilenga 3 Intended Category: Standards Track OpenLDAP Foundation 4 Expires in six months 4 November 2002 5 Updates: RFC 2595 7 Plain SASL Mechanism 8 10 Status of Memo 12 This document is an Internet-Draft and is in full conformance with all 13 provisions of Section 10 of RFC2026. 15 This document is intended to be, after appropriate review and 16 revision, submitted to the RFC Editor as a Standards Track document. 17 Distribution of this memo is unlimited. Technical discussion of this 18 document will take place on the IETF SASL mailing list 19 . Please send editorial comments directly to the 20 document editor . 22 Internet-Drafts are working documents of the Internet Engineering Task 23 Force (IETF), its areas, and its working groups. Note that other 24 groups may also distribute working documents as Internet-Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as ``work in progress.'' 30 The list of current Internet-Drafts can be accessed at 31 . The list of 32 Internet-Draft Shadow Directories can be accessed at 33 . 35 Copyright 2002, The Internet Society. All Rights Reserved. 37 Please see the Copyright section near the end of this document for 38 more information. 40 Abstract 42 This document defines a simple clear-text user/password Simple 43 Authentication and Security Layer (SASL) mechanism called the PLAIN 44 mechanism. The PLAIN mechanism intended to be used, in combination 45 with data confidentiality services provided by a lower layer, in 46 protocols which lack a simple password authentication command. 48 Conventions 50 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 51 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 52 document are to be interpreted as described in [KEYWORDS]. 54 1. Background and Intended Usage 56 Clear-text passwords are simple, interoperate with almost all existing 57 operating system authentication databases, and are useful for a smooth 58 transition to a more secure password-based authentication mechanism. 59 The drawback is that they are unacceptable for use over an unencrypted 60 network connection. 62 This document defines the PLAIN Simple Authentication and Security 63 Layer ([SASL]) mechanism for use in protocols with no clear-text login 64 command (e.g., ACAP). 66 The name associated with this mechanism is "PLAIN". 68 The PLAIN SASL mechanism does not provide a security layer. This 69 mechanism MUST NOT be used without adequate security protection as the 70 mechanism affords no integrity nor confidentiality protection itself. 71 The PLAIN SASL mechanism MUST NOT be advertised unless a strong 72 encryption layer, such as provided by Transport Layer Security 73 ([TLS]), is active. 75 This document updates RFC 2595, replacing Section 6. Changes since 76 RFC 2595 are detailed in Appendix A. 78 2. PLAIN SASL mechanism 80 The mechanism consists of a single message from the client to the 81 server. The client sends the authorization identity (identity to 82 login as), followed by a NUL character, followed by the authentication 83 identity (identity whose password will be used), followed by a NUL 84 character, followed by the clear-text password. The client may leave 85 the authorization identity empty if wishes the server to derive the 86 authorization identity from the provided the authentication identity. 88 The authorization identity (authzid), authentication identity 89 (authcid) and password (passwd) SHALL be transferred as [UTF-8] 90 encoded strings of printable [Unicode] characters in Unicode 91 Normalisation Form KC [NFKC] delimitated by the NUL (U+0000) 92 character. 94 The following characters are considered non-printable: 95 - control characters: U+0000..U+001F, U+007F..U+009F; 96 - replacement character: U+FFFD; and 97 - special characters and noncharacter: U+FEFF, U+FFFE, U+FFFF. 99 The server will verify the authentication identity (authcid) and 100 password (passwd) with the system authentication database and verify 101 that the authentication credentials permit the client to login as the 102 authorization identity (authzid). If both steps succeed, the user is 103 logged in. 105 The server MAY also use the password to initialize any new 106 authentication database, such as one suitable for [CRAM-MD5] or 107 [DIGEST-MD5]. 109 The formal grammar for the client message using Augmented BNF [ABNF] 110 follows. 112 message = [authzid] NUL authcid NUL passwd 113 authcid = 1*SAFE ; MUST accept up to 255 octets 114 authzid = 1*SAFE ; MUST accept up to 255 octets 115 passwd = 1*SAFE ; MUST accept up to 255 octets 116 NUL = %x00 118 SAFE = UTF1 / UTF2 / UTF3 / UTF4 / UTF5 / UTF6 / UTF7 119 ;; any UTF-8 encoded Unicode printable character 121 UTF1 = %x01-7F 122 UTF2 = %xC0-DF 1(UTF0) 123 UTF3 = %xE0-EF 2(UTF0) 124 UTF4 = %xF0-F7 3(UTF0) 125 UTF5 = %xF8-FB 4(UTF0) 126 UTF6 = %xFC-FD 5(UTF0) 127 UTF0 = %x80-BF 129 4. Example 131 Here is an example of how this might be used to initialize a CRAM-MD5 132 authentication database for ACAP. "C:" and "S:" indicate lines sent 133 by the client and server respectively. 135 S: * ACAP (SASL "CRAM-MD5") (STARTTLS) 136 C: a001 AUTHENTICATE "CRAM-MD5" 137 S: + "<1896.697170952@postoffice.reston.mci.net>" 138 C: "tim b913a602c7eda7a495b4e6e7334d3890" 139 S: a001 NO (TRANSITION-NEEDED) 140 "Please change your password, or use TLS to login" 141 C: a002 STARTTLS 142 S: a002 OK "Begin TLS negotiation now" 143 144 S: * ACAP (SASL "CRAM-MD5" "PLAIN" "EXTERNAL") 145 C: a003 AUTHENTICATE "PLAIN" {21+} 146 C: timtanstaaftanstaaf 147 S: a003 OK CRAM-MD5 password initialized 149 In this example, represents a single NUL (U+0000) character. 151 5. Security Considerations 153 The PLAIN mechanism relies on the TLS encryption layer for security. 154 When used without TLS, it is vulnerable to a common network 155 eavesdropping attack. Therefore PLAIN MUST NOT be advertised or used 156 unless a suitable TLS encryption layer is active or backwards 157 compatibility dictates otherwise. 159 When the PLAIN mechanism is used, the server gains the ability to 160 impersonate the user to all services with the same password regardless 161 of any encryption provided by TLS or other network privacy mechanisms. 162 While many other authentication mechanisms have similar weaknesses, 163 stronger SASL mechanisms such as the Kerberos-based GSSAPI mechanism 164 address this issue. Clients are encouraged to have an operational 165 mode where all mechanisms which are likely to reveal the user's 166 password to the server are disabled. 168 Clients are encouraged to have an operational mode where all 169 mechanisms which are likely to reveal the user's password to the 170 server are disabled. It is RECOMMENDED that this mode be the default. 172 General SASL security considerations apply to this mechanism. 174 6. IANA Considerations 176 It is requested that the SASL Mechanism registry [IANA-SASL] entry for 177 the PLAIN mechanism be updated to reflect that this document now 178 provides its technical specification. 180 To: iana@iana.org 181 Subject: Updated Registration of SASL mechanism PLAIN 182 SASL mechanism name: PLAIN 183 Security considerations: See RFC XXXX. 184 Published specification (optional, recommended): RFC XXXX 185 Person & email address to contact for further information: 186 Kurt Zeilenga 187 Chris Neuman 188 Intended usage: COMMON 189 Author/Change controller: IESG 190 Note: Updates existing entry for PLAIN 192 7. Acknowledgement 194 This document is a revision of RFC 2595 by Chris Newman. 196 8. Normative References 198 [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax 199 Specifications: ABNF", RFC 2234, November 1997. 201 [KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate 202 Requirement Levels", BCP 14 (also RFC 2119), March 1997. 204 [NFKC] Davis, M., M. Durst, "Unicode Standard Annex #15: Unicode 205 Normalisation Forms", An integral part of The Unicode 206 Standard, Version 3.2.0 207 (http://www.unicode.org/reports/tr15/tr15-22.html). 209 [SASL] Myers, J., "Simple Authentication and Security Layer 210 (SASL)", RFC 2222bis (a work in progress). 212 [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 213 3.2.0", defined by: The Unicode Standard, Version 3.0 214 (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), 215 as amended by the Unicode Standard Annex #28: Unicode 3.2 216 (http://www.unicode.org/reports/tr28/tr28-3.html). 218 [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 219 10646", RFC 2279, January 1998. 221 [TLS] T. Dierks, C. Allen, "The TLS Protocol Version 1.0", RFC 222 2246, January 1999. 224 9. Informative References 226 [CRAM-MD5] J. Klensin, R. Catoe, and P. Krumviede, "IMAP/POP 227 AUTHorize Extension for Simple Challenge/Response", RFC 228 2195, September 1997. 230 [DIGEST-MD5] P. Leach, C. Newman, "Using Digest Authentication as a 231 SASL Mechanism", RFC 2831, May 2000. 233 [IANA-SASL] IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL) 234 MECHANISMS", http://www.iana.org/assignments/sasl- 235 mechanisms. 237 10. Editor's Address 239 Kurt Zeilenga 240 OpenLDAP Foundation 242 Email: kurt@OpenLDAP.org 244 Appendix A. Changes since RFC 2595 246 This appendix is non-normative. 248 This document replaces Section 6 of RFC 2595. 250 The specification clarifies the normalized form to be used and details 251 which characters are considered to be printable. The ABNF grammar was 252 updated. 254 Additionally, a number of editorial changes were made. 256 Full Copyright Statement 258 Copyright 2002, The Internet Society. All Rights Reserved. 260 This document and translations of it may be copied and furnished to 261 others, and derivative works that comment on or otherwise explain it 262 or assist in its implementation may be prepared, copied, published and 263 distributed, in whole or in part, without restriction of any kind, 264 provided that the above copyright notice and this paragraph are 265 included on all such copies and derivative works. However, this 266 document itself may not be modified in any way, such as by removing 267 the copyright notice or references to the Internet Society or other 268 Internet organizations, except as needed for the purpose of 269 developing Internet standards in which case the procedures for 270 copyrights defined in the Internet Standards process must be followed, 271 or as required to translate it into languages other than English. 273 The limited permissions granted above are perpetual and will not be 274 revoked by the Internet Society or its successors or assigns. 276 This document and the information contained herein is provided on an 277 "AS IS" basis and THE AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET 278 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, 279 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 280 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 281 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.