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2 TLS Working Group V. Gupta
3 Internet-Draft Sun Labs
4 Expires: May 1, 2004 S. Blake-Wilson
5 BCI
6 B. Moeller
7 TBD
8 C. Hawk
9 Independent Consultant
10 N. Bolyard
11 Netscape
12 Nov. 2003
15 ECC Cipher Suites for TLS
16 <draft-ietf-tls-ecc-04.txt>
18 Status of this Memo
20 This document is an Internet-Draft and is in full conformance with
21 all provisions of Section 10 of RFC2026.
23 Internet-Drafts are working documents of the Internet Engineering
24 Task Force (IETF), its areas, and its working groups. Note that
25 other groups may also distribute working documents as Internet-
26 Drafts.
28 Internet-Drafts are draft documents valid for a maximum of six months
29 and may be updated, replaced, or obsoleted by other documents at any
30 time. It is inappropriate to use Internet-Drafts as reference
31 material or to cite them other than as "work in progress."
33 The list of current Internet-Drafts can be accessed at http://
34 www.ietf.org/ietf/1id-abstracts.txt.
36 The list of Internet-Draft Shadow Directories can be accessed at
37 http://www.ietf.org/shadow.html.
39 This Internet-Draft will expire on May 1, 2004.
41 Copyright Notice
43 Copyright (C) The Internet Society (2003). All Rights Reserved.
45 Abstract
47 This document describes new key exchange algorithms based on Elliptic
48 Curve Cryptography (ECC) for the TLS (Transport Layer Security)
49 protocol. In particular, it specifies the use of Elliptic Curve
50 Diffie-Hellman (ECDH) key agreement in a TLS handshake and the use of
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59 Elliptic Curve Digital Signature Algorithm (ECDSA) as a new
60 authentication mechanism.
62 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
63 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
64 document are to be interpreted as described in RFC 2119 [1].
66 Please send comments on this document to the TLS mailing list.
68 Table of Contents
70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
71 2. Key Exchange Algorithms . . . . . . . . . . . . . . . . . . 5
72 2.1 ECDH_ECDSA . . . . . . . . . . . . . . . . . . . . . . . . . 6
73 2.2 ECDHE_ECDSA . . . . . . . . . . . . . . . . . . . . . . . . 7
74 2.3 ECDH_RSA . . . . . . . . . . . . . . . . . . . . . . . . . . 7
75 2.4 ECDHE_RSA . . . . . . . . . . . . . . . . . . . . . . . . . 7
76 2.5 ECDH_anon . . . . . . . . . . . . . . . . . . . . . . . . . 7
77 3. Client Authentication . . . . . . . . . . . . . . . . . . . 9
78 3.1 ECDSA_sign . . . . . . . . . . . . . . . . . . . . . . . . . 9
79 3.2 ECDSA_fixed_ECDH . . . . . . . . . . . . . . . . . . . . . . 10
80 3.3 RSA_fixed_ECDH . . . . . . . . . . . . . . . . . . . . . . . 10
81 4. TLS Extensions for ECC . . . . . . . . . . . . . . . . . . . 11
82 5. Data Structures and Computations . . . . . . . . . . . . . . 12
83 5.1 Client Hello Extensions . . . . . . . . . . . . . . . . . . 12
84 5.2 Server Hello Extensions . . . . . . . . . . . . . . . . . . 14
85 5.3 Server Certificate . . . . . . . . . . . . . . . . . . . . . 15
86 5.4 Server Key Exchange . . . . . . . . . . . . . . . . . . . . 16
87 5.5 Certificate Request . . . . . . . . . . . . . . . . . . . . 20
88 5.6 Client Certificate . . . . . . . . . . . . . . . . . . . . . 21
89 5.7 Client Key Exchange . . . . . . . . . . . . . . . . . . . . 22
90 5.8 Certificate Verify . . . . . . . . . . . . . . . . . . . . . 24
91 5.9 Elliptic Curve Certificates . . . . . . . . . . . . . . . . 25
92 5.10 ECDH, ECDSA and RSA Computations . . . . . . . . . . . . . . 25
93 6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . 27
94 7. Security Considerations . . . . . . . . . . . . . . . . . . 29
95 8. Intellectual Property Rights . . . . . . . . . . . . . . . . 30
96 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 31
97 Normative References . . . . . . . . . . . . . . . . . . . . 32
98 Informative References . . . . . . . . . . . . . . . . . . . 33
99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 33
100 Full Copyright Statement . . . . . . . . . . . . . . . . . . 35
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115 1. Introduction
117 Elliptic Curve Cryptography (ECC) is emerging as an attractive
118 public-key cryptosystem for mobile/wireless environments. Compared
119 to currently prevalent cryptosystems such as RSA, ECC offers
120 equivalent security with smaller key sizes. This is illustrated in
121 the following table, based on [12], which gives approximate
122 comparable key sizes for symmetric- and asymmetric-key cryptosystems
123 based on the best-known algorithms for attacking them.
125 Symmetric | ECC | DH/DSA/RSA
126 -------------+---------+------------
127 80 | 163 | 1024
128 112 | 233 | 2048
129 128 | 283 | 3072
130 192 | 409 | 7680
131 256 | 571 | 15360
133 Table 1: Comparable key sizes (in bits)
136 Smaller key sizes result in power, bandwidth and computational
137 savings that make ECC especially attractive for constrained
138 environments.
140 This document describes additions to TLS to support ECC. In
141 particular, it defines
143 o the use of the Elliptic Curve Diffie-Hellman (ECDH) key agreement
144 scheme with long-term or ephemeral keys to establish the TLS
145 premaster secret, and
147 o the use of fixed-ECDH certificates and ECDSA for authentication of
148 TLS peers.
150 The remainder of this document is organized as follows. Section 2
151 provides an overview of ECC-based key exchange algorithms for TLS.
152 Section 3 describes the use of ECC certificates for client
153 authentication. TLS extensions that allow a client to negotiate the
154 use of specific curves and point formats are presented in Section 4.
155 Section 5 specifies various data structures needed for an ECC-based
156 handshake, their encoding in TLS messages and the processing of those
157 messages. Section 6 defines new ECC-based cipher suites and
158 identifies a small subset of these as recommended for all
159 implementations of this specification. Section 7, Section 8 and
160 Section 9 mention security considerations, intellectual property
161 rights, and acknowledgments, respectively. This is followed by a
162 list of references cited in this document and the authors' contact
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171 information.
173 Implementation of this specification requires familiarity with TLS
174 [2], TLS extensions [3] and ECC [4][5][6][8] .
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227 2. Key Exchange Algorithms
229 This document introduces five new ECC-based key exchange algorithms
230 for TLS. All of them use ECDH to compute the TLS premaster secret
231 and differ only in the lifetime of ECDH keys (long-term or ephemeral)
232 and the mechanism (if any) used to authenticate them. The derivation
233 of the TLS master secret from the premaster secret and the subsequent
234 generation of bulk encryption/MAC keys and initialization vectors is
235 independent of the key exchange algorithm and not impacted by the
236 introduction of ECC.
238 The table below summarizes the new key exchange algorithms which
239 mimic DH_DSS, DH_RSA, DHE_DSS, DHE_RSA and DH_anon (see [2]),
240 respectively.
242 Key
243 Exchange
244 Algorithm Description
245 --------- -----------
247 ECDH_ECDSA Fixed ECDH with ECDSA-signed certificates.
249 ECDHE_ECDSA Ephemeral ECDH with ECDSA signatures.
251 ECDH_RSA Fixed ECDH with RSA-signed certificates.
253 ECDHE_RSA Ephemeral ECDH with RSA signatures.
255 ECDH_anon Anonymous ECDH, no signatures.
258 Table 2: ECC key exchange algorithms
261 Note that the anonymous key exchange algorithm does not provide
262 authentication of the server or the client. Like other anonymous TLS
263 key exchanges, it is subject to man-in-the-middle attacks.
264 Implementations of this algorithm SHOULD provide authentication by
265 other means.
267 Note that there is no structural difference between ECDH and ECDSA
268 keys. A certificate issuer may use X509.v3 keyUsage and
269 extendedKeyUsage extensions to restrict the use of an ECC public key
270 to certain computations. This document refers to an ECC key as ECDH-
271 capable if its use in ECDH is permitted. ECDSA-capable is defined
272 similarly.
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283 Client Server
284 ------ ------
286 ClientHello -------->
287 ServerHello
288 Certificate*
289 ServerKeyExchange*
290 CertificateRequest*+
291 <-------- ServerHelloDone
292 Certificate*+
293 ClientKeyExchange
294 CertificateVerify*+
295 [ChangeCipherSpec]
296 Finished -------->
297 [ChangeCipherSpec]
298 <-------- Finished
300 Application Data <-------> Application Data
302 Figure 1: Message flow in a full TLS handshake
303 * message is not sent under some conditions
304 + message is not sent unless the client is
305 authenticated
308 Figure 1 shows all messages involved in the TLS key establishment
309 protocol (aka full handshake). The addition of ECC has direct impact
310 only on the ClientHello, the ServerHello, the server's Certificate
311 message, the ServerKeyExchange, the ClientKeyExchange, the
312 CertificateRequest, the client's Certificate message, and the
313 CertificateVerify. Next, we describe each ECC key exchange algorithm
314 in greater detail in terms of the content and processing of these
315 messages. For ease of exposition, we defer discussion of client
316 authentication and associated messages (identified with a + in Figure
317 1) until Section 3 and of the optional ECC-specific extensions (which
318 impact the Hello messages) until Section 4.
320 2.1 ECDH_ECDSA
322 In ECDH_ECDSA, the server's certificate MUST contain an ECDH-capable
323 public key and be signed with ECDSA.
325 A ServerKeyExchange MUST NOT be sent (the server's certificate
326 contains all the necessary keying information required by the client
327 to arrive at the premaster secret).
329 The client MUST generate an ECDH key pair on the same curve as the
330 server's long-term public key and send its public key in the
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339 ClientKeyExchange message (except when using client authentication
340 algorithm ECDSA_fixed_ECDH or RSA_fixed_ECDH, in which case the
341 modifications from section Section 3.2 or Section 3.3 apply).
343 Both client and server MUST perform an ECDH operation and use the
344 resultant shared secret as the premaster secret. All ECDH
345 calculations are performed as specified in Section 5.10
347 2.2 ECDHE_ECDSA
349 In ECDHE_ECDSA, the server's certificate MUST contain an ECDSA-
350 capable public key and be signed with ECDSA.
352 The server MUST send its ephemeral ECDH public key and a
353 specification of the corresponding curve in the ServerKeyExchange
354 message. These parameters MUST be signed with ECDSA using the
355 private key corresponding to the public key in the server's
356 Certificate.
358 The client MUST generate an ECDH key pair on the same curve as the
359 server's ephemeral ECDH key and send its public key in the
360 ClientKeyExchange message.
362 Both client and server MUST perform an ECDH operation (Section 5.10)
363 and use the resultant shared secret as the premaster secret.
365 2.3 ECDH_RSA
367 This key exchange algorithm is the same as ECDH_ECDSA except the
368 server's certificate MUST be signed with RSA rather than ECDSA.
370 2.4 ECDHE_RSA
372 This key exchange algorithm is the same as ECDHE_ECDSA except the
373 server's certificate MUST contain an RSA public key authorized for
374 signing and the signature in the ServerKeyExchange message MUST be
375 computed with the corresponding RSA private key. The server
376 certificate MUST be signed with RSA.
378 2.5 ECDH_anon
380 In ECDH_anon, the server's Certificate, the CertificateRequest, the
381 client's Certificate, and the CertificateVerify messages MUST NOT be
382 sent.
384 The server MUST send an ephemeral ECDH public key and a specification
385 of the corresponding curve in the ServerKeyExchange message. These
386 parameters MUST NOT be signed.
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395 The client MUST generate an ECDH key pair on the same curve as the
396 server's ephemeral ECDH key and send its public key in the
397 ClientKeyExchange message.
399 Both client and server MUST perform an ECDH operation and use the
400 resultant shared secret as the premaster secret. All ECDH
401 calculations are performed as specified in Section 5.10
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451 3. Client Authentication
453 This document defines three new client authentication mechanisms
454 named after the type of client certificate involved: ECDSA_sign,
455 ECDSA_fixed_ECDH and RSA_fixed_ECDH. The ECDSA_sign mechanism is
456 usable with any of the non-anonymous ECC key exchange algorithms
457 described in Section 2 as well as other non-anonymous (non-ECC) key
458 exchange algorithms defined in TLS [2]. The ECDSA_fixed_ECDH and
459 RSA_fixed_ECDH mechanisms are usable with ECDH_ECDSA and ECDH_RSA.
460 Their use with ECDHE_ECDSA and ECDHE_RSA is prohibited because the
461 use of a long-term ECDH client key would jeopardize the forward
462 secrecy property of these algorithms.
464 The server can request ECC-based client authentication by including
465 one or more of these certificate types in its CertificateRequest
466 message. The server MUST NOT include any certificate types that are
467 prohibited for the negotiated key exchange algorithm. The client
468 must check if it possesses a certificate appropriate for any of the
469 methods suggested by the server and is willing to use it for
470 authentication.
472 If these conditions are not met, the client should send a client
473 Certificate message containing no certificates. In this case, the
474 ClientKeyExchange should be sent as described in Section 2 and the
475 CertificateVerify should not be sent. If the server requires client
476 authentication, it may respond with a fatal handshake failure alert.
478 If the client has an appropriate certificate and is willing to use it
479 for authentication, it MUST send that certificate in the client's
480 Certificate message (as per Section 5.6) and prove possession of the
481 private key corresponding to the certified key. The process of
482 determining an appropriate certificate and proving possession is
483 different for each authentication mechanism and described below.
485 NOTE: It is permissible for a server to request (and the client to
486 send) a client certificate of a different type than the server
487 certificate.
489 3.1 ECDSA_sign
491 To use this authentication mechanism, the client MUST possess a
492 certificate containing an ECDSA-capable public key and signed with
493 ECDSA.
495 The client MUST prove possession of the private key corresponding to
496 the certified key by including a signature in the CertificateVerify
497 message as described in Section 5.8.
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507 3.2 ECDSA_fixed_ECDH
509 To use this authentication mechanism, the client MUST possess a
510 certificate containing an ECDH-capable public key and that
511 certificate MUST be signed with ECDSA. Furthermore, the client's
512 ECDH key MUST be on the same elliptic curve as the server's long-term
513 (certified) ECDH key.
515 When using this authentication mechanism, the client MUST send an
516 empty ClientKeyExchange as described in Section 5.7 and MUST NOT send
517 the CertificateVerify message. The ClientKeyExchange is empty since
518 the client's ECDH public key required by the server to compute the
519 premaster secret is available inside the client's certificate. The
520 client's ability to arrive at the same premaster secret as the server
521 (demonstrated by a successful exchange of Finished messages) proves
522 possession of the private key corresponding to the certified public
523 key and the CertificateVerify message is unnecessary.
525 3.3 RSA_fixed_ECDH
527 This authentication mechanism is identical to ECDSA_fixed_ECDH except
528 the client's certificate MUST be signed with RSA.
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563 4. TLS Extensions for ECC
565 Two new TLS extensions --- (i) the Supported Elliptic Curves
566 Extension, and (ii) the Supported Point Formats Extension --- allow a
567 client to negotiate the use of specific curves and point formats
568 (e.g. compressed v/s uncompressed), respectively. These extensions
569 are especially relevant for constrained clients that may only support
570 a limited number of curves or point formats. They follow the
571 general approach outlined in [3]. The client enumerates the curves
572 and point formats it supports by including the appropriate extensions
573 in its ClientHello message. By echoing that extension in its
574 ServerHello, the server agrees to restrict its key selection or
575 encoding to the choices specified by the client.
577 A TLS client that proposes ECC cipher suites in its ClientHello
578 message SHOULD include these extensions. Servers implementing ECC
579 cipher suites MUST support these extensions and negotiate the use of
580 an ECC cipher suite only if they can complete the handshake while
581 limiting themselves to the curves and compression techniques
582 enumerated by the client. This eliminates the possibility that a
583 negotiated ECC handshake will be subsequently aborted due to a
584 client's inability to deal with the server's EC key.
586 These extensions MUST NOT be included if the client does not propose
587 any ECC cipher suites. A client that proposes ECC cipher suites may
588 choose not to include these extension. In this case, the server is
589 free to choose any one of the elliptic curves or point formats listed
590 in Section 5. That section also describes the structure and
591 processing of these extensions in greater detail.
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619 5. Data Structures and Computations
621 This section specifies the data structures and computations used by
622 ECC-based key mechanisms specified in Section 2, Section 3 and
623 Section 4. The presentation language used here is the same as that
624 used in TLS [2]. Since this specification extends TLS, these
625 descriptions should be merged with those in the TLS specification and
626 any others that extend TLS. This means that enum types may not
627 specify all possible values and structures with multiple formats
628 chosen with a select() clause may not indicate all possible cases.
630 5.1 Client Hello Extensions
632 When this message is sent:
634 The ECC extensions SHOULD be sent along with any ClientHello message
635 that proposes ECC cipher suites.
637 Meaning of this message:
639 These extensions allow a constrained client to enumerate the elliptic
640 curves and/or point formats it supports.
642 Structure of this message:
644 The general structure of TLS extensions is described in [3] and this
645 specification adds two new types to ExtensionType.
648 enum { ellptic_curves(6), ec_point_formats(7) } ExtensionType;
650 elliptic_curves: Indicates the set of elliptic curves supported by
651 the client. For this extension, the opaque extension_data field
652 contains EllipticCurveList.
654 ec_point_formats: Indicates the set of point formats supported by
655 the client. For this extension, the opaque extension_data field
656 contains ECPointFormatList.
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675 enum {
676 sect163k1 (1), sect163r1 (2), sect163r2 (3),
677 sect193r1 (4), sect193r2 (5), sect233k1 (6),
678 sect233r1 (7), sect239k1 (8), sect283k1 (9),
679 sect283r1 (10), sect409k1 (11), sect409r1 (12),
680 sect571k1 (13), sect571r1 (14), secp160k1 (15),
681 secp160r1 (16), secp160r2 (17), secp192k1 (18),
682 secp192r1 (19), secp224k1 (20), secp224r1 (21),
683 secp256k1 (22), secp256r1 (23), secp384r1 (24),
684 secp521r1 (25), reserved (240..247),
685 arbitrary_explicit_prime_curves(253),
686 arbitrary_explicit_char2_curves(254),
687 (255)
688 } NamedCurve;
690 sect163k1, etc: Indicates support of the corresponding named curve
691 specified in SEC 2 [10]. Note that many of these curves are also
692 recommended in ANSI X9.62 [6], and FIPS 186-2 [8]. Values 240
693 through 247 are reserved for private use. Values 253 and 254
694 indicate that the client supports arbitrary prime and
695 charactersitic two curves, respectively (the curve parameters must
696 be encoded explicitly in ECParameters).
699 struct {
700 NamedCurve elliptic_curve_list<1..2^16-1>
701 } EllipticCurveList;
704 As an example, a client that only supports secp192r1 (aka NIST P-192)
705 and secp192r1 (aka NIST P-224) would include an elliptic_curves
706 extension with the following octets:
708 00 06 00 02 13 14
710 A client that supports arbitrary explicit binary polynomial curves
711 would include an extension with the following octets:
713 00 06 00 01 fe
716 enum { uncompressed (0), ansiX963_compressed (1), ansiX963_hybrid (2) }
717 ECPointFormat;
719 struct {
720 ECPointFormat ec_point_format_list<1..2^16-1>
721 } ECPointFormatList;
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731 A client that only supports the uncompressed point format includes an
732 extension with the following octets:
734 00 07 00 01 00
736 A client that prefers the use of the ansiX963_compressed format over
737 uncompressed may indicate that preference by including an extension
738 with the following octets:
740 00 07 00 02 01 00
742 Actions of the sender:
744 A client that proposes ECC cipher suites in its ClientHello appends
745 these extensions (along with any others) enumerating the curves and
746 point formats it supports.
748 Actions of the receiver:
750 A server that receives a ClientHello containing one or both of these
751 extensions MUST use the client's enumerated capabilities to guide its
752 selection of an appropriate cipher suite. One of the proposed ECC
753 cipher suites must be negotiated only if the server can successfully
754 complete the handshake while using the curves and point formats
755 supported by the client.
757 NOTE: A server participating in an ECDHE-ECDSA key exchange may use
758 different curves for (i) the ECDSA key in its certificate, and (ii)
759 the ephemeral ECDH key in the ServerKeyExchange message. The server
760 must consider the "elliptic_curves" extension in selecting both of
761 these curves.
763 If a server does not understand the "elliptic_curves" extension or is
764 unable to complete the ECC handshake while restricting itself to the
765 enumerated curves, it MUST NOT negotiate the use of an ECC cipher
766 suite. Depending on what other cipher suites are proposed by the
767 client and supported by the server, this may result in a fatal
768 handshake failure alert due to the lack of common cipher suites.
770 5.2 Server Hello Extensions
772 When this message is sent:
774 The ServerHello ECC extensions are sent in response to a Client Hello
775 message containing ECC extensions when negotiating an ECC cipher
776 suite.
778 Meaning of this message:
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787 These extensions indicate the server's agreement to use only the
788 elliptic curves and point formats supported by the client during the
789 ECC-based key exchange.
791 Structure of this message:
793 The ECC extensions echoed by the server are the same as those in the
794 ClientHello except the "extension_data" field is empty.
796 For example, a server indicates its acceptance of the client's
797 elliptic_curves extension by sending an extension with the following
798 octets:
800 00 06 00 00
802 Actions of the sender:
804 A server makes sure that it can complete a proposed ECC key exchange
805 mechanism by restricting itself to the curves/point formats supported
806 by the client before sending these extensions.
808 Actions of the receiver:
810 A client that receives a ServerHello with ECC extensions proceeds
811 with an ECC key exchange assured that it will be able to handle the
812 server's EC key(s).
814 5.3 Server Certificate
816 When this message is sent:
818 This message is sent in all non-anonymous ECC-based key exchange
819 algorithms.
821 Meaning of this message:
823 This message is used to authentically convey the server's static
824 public key to the client. The following table shows the server
825 certificate type appropriate for each key exchange algorithm. ECC
826 public keys must be encoded in certificates as described in Section
827 5.9.
829 NOTE: The server's Certificate message is capable of carrying a chain
830 of certificates. The restrictions mentioned in Table 3 apply only to
831 the server's certificate (first in the chain).
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843 Key Exchange Algorithm Server Certificate Type
844 ---------------------- -----------------------
846 ECDH_ECDSA Certificate must contain an
847 ECDH-capable public key. It
848 must be signed with ECDSA.
850 ECDHE_ECDSA Certificate must contain an
851 ECDSA-capable public key. It
852 must be signed with ECDSA.
854 ECDH_RSA Certificate must contain an
855 ECDH-capable public key. It
856 must be signed with RSA.
858 ECDHE_RSA Certificate must contain an
859 RSA public key authorized for
860 use in digital signatures. It
861 must be signed with RSA.
863 Table 3: Server certificate types
866 Structure of this message:
868 Identical to the TLS Certificate format.
870 Actions of the sender:
872 The server constructs an appropriate certificate chain and conveys it
873 to the client in the Certificate message.
875 Actions of the receiver:
877 The client validates the certificate chain, extracts the server's
878 public key, and checks that the key type is appropriate for the
879 negotiated key exchange algorithm.
881 5.4 Server Key Exchange
883 When this message is sent:
885 This message is sent when using the ECDHE_ECDSA, ECDHE_RSA and
886 ECDH_anon key exchange algorithms.
888 Meaning of this message:
890 This message is used to convey the server's ephemeral ECDH public key
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899 (and the corresponding elliptic curve domain parameters) to the
900 client.
902 Structure of this message:
904 enum { explicit_prime (1), explicit_char2 (2),
905 named_curve (3), (255) } ECCurveType;
907 explicit_prime: Indicates the elliptic curve domain parameters are
908 conveyed verbosely, and the underlying finite field is a prime
909 field.
911 explicit_char2: Indicates the elliptic curve domain parameters are
912 conveyed verbosely, and the underlying finite field is a
913 characteristic 2 field.
915 named_curve: Indicates that a named curve is used. This option
916 SHOULD be used when applicable.
919 struct {
920 opaque a <1..2^8-1>;
921 opaque b <1..2^8-1>;
922 opaque seed <0..2^8-1>;
923 } ECCurve;
925 a, b: These parameters specify the coefficients of the elliptic
926 curve. Each value contains the byte string representation of a
927 field element following the conversion routine in Section 4.3.3 of
928 ANSI X9.62 [6].
930 seed: This is an optional parameter used to derive the coefficients
931 of a randomly generated elliptic curve.
934 struct {
935 opaque point <1..2^8-1>;
936 } ECPoint;
938 point: This is the byte string representation of an elliptic curve
939 point following the conversion routine in Section 4.3.6 of ANSI
940 X9.62 [6]. Note that this byte string may represent an elliptic
941 curve point in compressed or uncompressed form. Implementations
942 of this specification MUST support the uncompressed form and MAY
943 support the compressed form.
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955 enum { ec_basis_trinomial, ec_basis_pentanomial } ECBasisType;
957 ec_basis_trinomial: Indicates representation of a characteristic two
958 field using a trinomial basis.
960 ec_basis_pentanomial: Indicates representation of a characteristic
961 two field using a pentanomial basis.
964 struct {
965 ECCurveType curve_type;
966 select (curve_type) {
967 case explicit_prime:
968 opaque prime_p <1..2^8-1>;
969 ECCurve curve;
970 ECPoint base;
971 opaque order <1..2^8-1>;
972 opaque cofactor <1..2^8-1>;
973 case explicit_char2:
974 uint16 m;
975 ECBasisType basis;
976 select (basis) {
977 case ec_trinomial:
978 opaque k <1..2^8-1>;
979 case ec_pentanomial:
980 opaque k1 <1..2^8-1>;
981 opaque k2 <1..2^8-1>;
982 opaque k3 <1..2^8-1>;
983 };
984 ECCurve curve;
985 ECPoint base;
986 opaque order <1..2^8-1>;
987 opaque cofactor <1..2^8-1>;
988 case named_curve:
989 NamedCurve namedcurve;
990 };
991 } ECParameters;
993 curve_type: This identifies the type of the elliptic curve domain
994 parameters.
996 prime_p: This is the odd prime defining the field Fp.
998 curve: Specifies the coefficients a and b (and optional seed) of the
999 elliptic curve E.
1001 base: Specifies the base point G on the elliptic curve.
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1011 order: Specifies the order n of the base point.
1013 cofactor: Specifies the cofactor h = #E(Fq)/n, where #E(Fq)
1014 represents the number of points on the elliptic curve E defined
1015 over the field Fq.
1017 m: This is the degree of the characteristic-two field F2^m.
1019 k: The exponent k for the trinomial basis representation x^m + x^k
1020 +1.
1022 k1, k2, k3: The exponents for the pentanomial representation x^m +
1023 x^k3 + x^k2 + x^k1 + 1 (such that k3 > k2 > k1).
1025 namedcurve: Specifies a recommended set of elliptic curve domain
1026 parameters. All enum values of NamedCurve are allowed except for
1027 arbitrary_explicit_prime_curves(253) and
1028 arbitrary_explicit_char2_curves(254). These two values are only
1029 allowed in the ClientHello extension.
1032 struct {
1033 ECParameters curve_params;
1034 ECPoint public;
1035 } ServerECDHParams;
1037 curve_params: Specifies the elliptic curve domain parameters
1038 associated with the ECDH public key.
1040 public: The ephemeral ECDH public key.
1042 The ServerKeyExchange message is extended as follows.
1044 enum { ec_diffie_hellman } KeyExchangeAlgorithm;
1046 ec_diffie_hellman: Indicates the ServerKeyExchange message contains
1047 an ECDH public key.
1050 select (KeyExchangeAlgorithm) {
1051 case ec_diffie_hellman:
1052 ServerECDHParams params;
1053 Signature signed_params;
1054 } ServerKeyExchange;
1056 params: Specifies the ECDH public key and associated domain
1057 parameters.
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1067 signed_params: A hash of the params, with the signature appropriate
1068 to that hash applied. The private key corresponding to the
1069 certified public key in the server's Certificate message is used
1070 for signing.
1073 enum { ecdsa } SignatureAlgorithm;
1076 select (SignatureAlgorithm) {
1077 case ecdsa:
1078 digitally-signed struct {
1079 opaque sha_hash[sha_size];
1080 };
1081 } Signature;
1083 NOTE: SignatureAlgorithm is 'rsa' for the ECDHE_RSA key exchange
1084 algorithm and 'anonymous' for ECDH_anon. These cases are defined in
1085 TLS [2]. SignatureAlgorithm is 'ecdsa' for ECDHE_ECDSA. ECDSA
1086 signatures are generated and verified as described in Section 5.10.
1087 As per ANSI X9.62, an ECDSA signature consists of a pair of integers
1088 r and s. These integers are both converted into byte strings of the
1089 same length as the curve order n using the conversion routine
1090 specified in Section 4.3.1 of [6]. The two byte strings are
1091 concatenated, and the result is placed in the signature field.
1093 Actions of the sender:
1095 The server selects elliptic curve domain parameters and an ephemeral
1096 ECDH public key corresponding to these parameters according to the
1097 ECKAS-DH1 scheme from IEEE 1363 [5]. It conveys this information to
1098 the client in the ServerKeyExchange message using the format defined
1099 above.
1101 Actions of the recipient:
1103 The client verifies the signature (when present) and retrieves the
1104 server's elliptic curve domain parameters and ephemeral ECDH public
1105 key from the ServerKeyExchange message.
1107 5.5 Certificate Request
1109 When this message is sent:
1111 This message is sent when requesting client authentication.
1113 Meaning of this message:
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1123 The server uses this message to suggest acceptable client
1124 authentication methods.
1126 Structure of this message:
1128 The TLS CertificateRequest message is extended as follows.
1130 enum {
1131 ecdsa_sign(?), rsa_fixed_ecdh(?),
1132 ecdsa_fixed_ecdh(?), (255)
1133 } ClientCertificateType;
1135 ecdsa_sign, etc Indicates that the server would like to use the
1136 corresponding client authentication method specified in Section 3.
1138 EDITOR: The values used for ecdsa_sign, rsa_fixed_ecdh, and
1139 ecdsa_fixed_ecdh have been left as ?. These values will be
1140 assigned when this draft progresses to RFC. Earlier versions of
1141 this draft used the values 5, 6, and 7 - however these values have
1142 been removed since they are used differently by SSL 3.0 [13] and
1143 their use by TLS is being deprecated.
1145 Actions of the sender:
1147 The server decides which client authentication methods it would like
1148 to use, and conveys this information to the client using the format
1149 defined above.
1151 Actions of the receiver:
1153 The client determines whether it has an appropriate certificate for
1154 use with any of the requested methods, and decides whether or not to
1155 proceed with client authentication.
1157 5.6 Client Certificate
1159 When this message is sent:
1161 This message is sent in response to a CertificateRequest when a
1162 client has a suitable certificate.
1164 Meaning of this message:
1166 This message is used to authentically convey the client's static
1167 public key to the server. The following table summarizes what client
1168 certificate types are appropriate for the ECC-based client
1169 authentication mechanisms described in Section 3. ECC public keys
1170 must be encoded in certificates as described in Section 5.9.
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1179 NOTE: The client's Certificate message is capable of carrying a chain
1180 of certificates. The restrictions mentioned in Table 4 apply only to
1181 the client's certificate (first in the chain).
1184 Client
1185 Authentication Method Client Certificate Type
1186 --------------------- -----------------------
1188 ECDSA_sign Certificate must contain an
1189 ECDSA-capable public key and
1190 be signed with ECDSA.
1192 ECDSA_fixed_ECDH Certificate must contain an
1193 ECDH-capable public key on the
1194 same elliptic curve as the server's
1195 long-term ECDH key. This certificate
1196 must be signed with ECDSA.
1198 RSA_fixed_ECDH Certificate must contain an
1199 ECDH-capable public key on the
1200 same elliptic curve as the server's
1201 long-term ECDH key. This certificate
1202 must be signed with RSA.
1204 Table 4: Client certificate types
1207 Structure of this message:
1209 Identical to the TLS client Certificate format.
1211 Actions of the sender:
1213 The client constructs an appropriate certificate chain, and conveys
1214 it to the server in the Certificate message.
1216 Actions of the receiver:
1218 The TLS server validates the certificate chain, extracts the client's
1219 public key, and checks that the key type is appropriate for the
1220 client authentication method.
1222 5.7 Client Key Exchange
1224 When this message is sent:
1226 This message is sent in all key exchange algorithms. If client
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1235 authentication with ECDSA_fixed_ECDH or RSA_fixed_ECDH is used, this
1236 message is empty. Otherwise, it contains the client's ephemeral ECDH
1237 public key.
1239 Meaning of the message:
1241 This message is used to convey ephemeral data relating to the key
1242 exchange belonging to the client (such as its ephemeral ECDH public
1243 key).
1245 Structure of this message:
1247 The TLS ClientKeyExchange message is extended as follows.
1249 enum { yes, no } EphemeralPublicKey;
1251 yes, no: Indicates whether or not the client is providing an
1252 ephemeral ECDH public key. (In ECC ciphersuites, this is "yes"
1253 except when the client uses the ECDSA_fixed_ECDH or RSA_fixed_ECDH
1254 client authentication mechanism.)
1257 struct {
1258 select (EphemeralPublicKey) {
1259 case yes: ECPoint ecdh_Yc;
1260 case no: struct { };
1261 } ecdh_public;
1262 } ClientECDiffieHellmanPublic;
1264 ecdh_Yc: Contains the client's ephemeral ECDH public key.
1267 struct {
1268 select (KeyExchangeAlgorithm) {
1269 case ec_diffie_hellman: ClientECDiffieHellmanPublic;
1270 } exchange_keys;
1271 } ClientKeyExchange;
1273 Actions of the sender:
1275 The client selects an ephemeral ECDH public key corresponding to the
1276 parameters it received from the server according to the ECKAS-DH1
1277 scheme from IEEE 1363 [5]. It conveys this information to the client
1278 in the ClientKeyExchange message using the format defined above.
1280 Actions of the recipient:
1282 The server retrieves the client's ephemeral ECDH public key from the
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1291 ClientKeyExchange message and checks that it is on the same elliptic
1292 curve as the server's ECDH key.
1294 5.8 Certificate Verify
1296 When this message is sent:
1298 This message is sent when the client sends a client certificate
1299 containing a public key usable for digital signatures, e.g. when the
1300 client is authenticated using the ECDSA_sign mechanism.
1302 Meaning of the message:
1304 This message contains a signature that proves possession of the
1305 private key corresponding to the public key in the client's
1306 Certificate message.
1308 Structure of this message:
1310 The TLS CertificateVerify message is extended as follows.
1312 enum { ecdsa } SignatureAlgorithm;
1314 select (SignatureAlgorithm) {
1315 case ecdsa:
1316 digitally-signed struct {
1317 opaque sha_hash[sha_size];
1318 };
1319 } Signature;
1321 For the ecdsa case, the signature field in the CertificateVerify
1322 message contains an ECDSA signature computed over handshake messages
1323 exchanged so far. ECDSA signatures are computed as described in
1324 Section 5.10. As per ANSI X9.62, an ECDSA signature consists of a
1325 pair of integers r and s. These integers are both converted into
1326 byte strings of the same length as the curve order n using the
1327 conversion routine specified in Section 4.3.1 of [6]. The two byte
1328 strings are concatenated, and the result is placed in the signature
1329 field.
1331 Actions of the sender:
1333 The client computes its signature over all handshake messages sent or
1334 received starting at client hello up to but not including this
1335 message. It uses the private key corresponding to its certified
1336 public key to compute the signature which is conveyed in the format
1337 defined above.
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1347 Actions of the receiver:
1349 The server extracts the client's signature from the CertificateVerify
1350 message, and verifies the signature using the public key it received
1351 in the client's Certificate message.
1353 5.9 Elliptic Curve Certificates
1355 X509 certificates containing ECC public keys or signed using ECDSA
1356 MUST comply with [11]. Clients SHOULD use the elliptic curve domain
1357 parameters recommended in ANSI X9.62 [6], FIPS 186-2 [8], and SEC 2
1358 [10].
1360 5.10 ECDH, ECDSA and RSA Computations
1362 All ECDH calculations (including parameter and key generation as well
1363 as the shared secret calculation) MUST be performed according to [5]
1364 using
1366 o the ECKAS-DH1 scheme with the ECSVDP-DH secret value derivation
1367 primitive, the KDF1 key derivation function using SHA-1 [7], and
1368 null key derivation parameters "P" for elliptic curve parameters
1369 where field elements are represented as octet strings of length 24
1370 or less (using the IEEE 1363 FE2OSP); in this case, the premaster
1371 secret is the output of the ECKAS-DH1 scheme, i.e. the 20-byte
1372 SHA-1 output from the KDF.
1374 o the ECKAS-DH1 scheme with the identity map as key derivation
1375 function for elliptic curve parameters where field elements are
1376 represented as octet strings of length more than 24; in this case,
1377 the premaster secret is the x-coordinate of the ECDH shared secret
1378 elliptic curve point, i.e. the octet string Z in IEEE 1363
1379 terminology.
1381 Note that a new extension may be introduced in the future to allow
1382 the use of a different KDF during computation of the premaster
1383 secret. In this event, the new KDF would be used in place of the
1384 process detailed above. This may be desirable, for example, to
1385 support compatibility with the planned NIST key agreement standard.
1387 All ECDSA computations MUST be performed according to ANSI X9.62 [6]
1388 or its successors. Data to be signed/verified is hashed and the
1389 result run directly through the ECDSA algorithm with no additional
1390 hashing. The default hash function is SHA-1 [7] and sha_size (see
1391 Section 5.4 and Section 5.8) is 20. However, an alternative hash
1392 function, such as one of the new SHA hash functions specified in FIPS
1393 180-2 [7], may be used instead if the certificate containing the EC
1394 public key explicitly requires use of another hash function.
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1403 All RSA signatures must be generated and verified according to PKCS#1
1404 [9].
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1459 6. Cipher Suites
1461 The table below defines new ECC cipher suites that use the key
1462 exchange algorithms specified in Section 2.
1464 EDITOR: Most of the cipher suites below have been left as ??. The
1465 values 47-4C correspond to cipher suites which are known to have been
1466 implemented and are therefore proposed here. The final determination
1467 of cipher suite numbers will occur when this draft progresses to RFC.
1468 Implementers using the values 47-4C should therefore be wary that
1469 these values may change.
1471 CipherSuite TLS_ECDH_ECDSA_WITH_NULL_SHA = { 0x00, 0x47 }
1472 CipherSuite TLS_ECDH_ECDSA_WITH_RC4_128_SHA = { 0x00, 0x48 }
1473 CipherSuite TLS_ECDH_ECDSA_WITH_DES_CBC_SHA = { 0x00, 0x49 }
1474 CipherSuite TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA = { 0x00, 0x4A }
1475 CipherSuite TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA = { 0x00, 0x4B }
1476 CipherSuite TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA = { 0x00, 0x4C }
1478 CipherSuite TLS_ECDHE_ECDSA_WITH_NULL_SHA = { 0x00, 0x?? }
1479 CipherSuite TLS_ECDHE_ECDSA_WITH_RC4_128_SHA = { 0x00, 0x?? }
1480 CipherSuite TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA = { 0x00, 0x?? }
1481 CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA = { 0x00, 0x?? }
1482 CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA = { 0x00, 0x?? }
1484 CipherSuite TLS_ECDH_RSA_WITH_NULL_SHA = { 0x00, 0x?? }
1485 CipherSuite TLS_ECDH_RSA_WITH_RC4_128_SHA = { 0x00, 0x?? }
1486 CipherSuite TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00, 0x?? }
1487 CipherSuite TLS_ECDH_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x?? }
1488 CipherSuite TLS_ECDH_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x?? }
1490 CipherSuite TLS_ECDHE_RSA_WITH_NULL_SHA = { 0x00, 0x?? }
1491 CipherSuite TLS_ECDHE_RSA_WITH_RC4_128_SHA = { 0x00, 0x?? }
1492 CipherSuite TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00, 0x?? }
1493 CipherSuite TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x?? }
1494 CipherSuite TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x?? }
1496 CipherSuite TLS_ECDH_anon_NULL_WITH_SHA = { 0x00, 0x?? }
1497 CipherSuite TLS_ECDH_anon_WITH_RC4_128_SHA = { 0x00, 0x?? }
1498 CipherSuite TLS_ECDH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00, 0x?? }
1499 CipherSuite TLS_ECDH_anon_WITH_AES_128_CBC_SHA = { 0x00, 0x?? }
1500 CipherSuite TLS_ECDH_anon_WITH_AES_256_CBC_SHA = { 0x00, 0x?? }
1502 Table 5: TLS ECC cipher suites
1505 The key exchange method, cipher, and hash algorithm for each of these
1506 cipher suites are easily determined by examining the name. Ciphers
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1515 other than AES ciphers, and hash algorithms are defined in [2]. AES
1516 ciphers are defined in [14].
1518 Server implementations SHOULD support all of the following cipher
1519 suites, and client implementations SHOULD support at least one of
1520 them: TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA,
1521 TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA,
1522 TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, and
1523 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA.
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1571 7. Security Considerations
1573 This document is based on [2], [5], [6] and [14]. The appropriate
1574 security considerations of those documents apply.
1576 For ECDH (Section 5.10), this document specifies two different ways
1577 to compute the premaster secret. The choice of the method is
1578 determined by the elliptic curve. Earlier versions of this
1579 specification used the KDF1 key derivation function with SHA-1 in all
1580 cases; the current version keeps this key derivation function only
1581 for curves where field elements are represented as octet strings of
1582 length 24 or less (i.e. up to 192 bits), but omits it for larger
1583 curves.
1585 Rationale: Using KDF1 with SHA-1 limits the security to at most 160
1586 bits, independently of the elliptic curve used for ECDH. For large
1587 curves, this would result in worse security than expected. Using a
1588 specific key derivation function for ECDH is not really necessary as
1589 TLS always uses its PRF to derive the master secret from the
1590 premaster secret. For large curves, the current specification
1591 handles ECDH like the basic TLS specification [14] handles standard
1592 DH. For smaller curves where the extra KDF1 step does not weaken
1593 security, the current specification keeps the KDF1 step to obtain
1594 compatibility with existing implementations of earlier versions of
1595 this specification. Note that the threshold for switching between
1596 the two ECDH calculation methods is necessarily somewhat arbitrary;
1597 192-bit ECC corresponds to approximately 96 bits of security in the
1598 light of square root attacks, so the 160 bits provided by SHA-1 are
1599 comfortable at this limit.
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1627 8. Intellectual Property Rights
1629 The IETF has been notified of intellectual property rights claimed in
1630 regard to the specification contained in this document. For more
1631 information, consult the online list of claimed rights (http://
1632 www.ietf.org/ipr.html).
1634 The IETF takes no position regarding the validity or scope of any
1635 intellectual property or other rights that might be claimed to
1636 pertain to the implementation or use of the technology described in
1637 this document or the extent to which any license under such rights
1638 might or might not be available; neither does it represent that it
1639 has made any effort to identify any such rights. Information on the
1640 IETF's procedures with respect to rights in standards-track and
1641 standards-related documentation can be found in [15]. Copies of
1642 claims of rights made available for publication and any assurances of
1643 licenses to be made available, or the result of an attempt made to
1644 obtain a general license or permission for the use of such
1645 proprietary rights by implementers or users of this specification can
1646 be obtained from the IETF Secretariat.
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1683 9. Acknowledgments
1685 The authors wish to thank Bill Anderson and Tim Dierks.
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1739 Normative References
1741 [1] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
1742 Levels", RFC 2119, March 1997.
1744 [2] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
1745 2246, January 1999.
1747 [3] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J. and
1748 T. Wright, "Transport Layer Security (TLS) Extensions", RFC
1749 3546, June 2003.
1751 [4] SECG, "Elliptic Curve Cryptography", SEC 1, 2000, <http://
1752 www.secg.org/>.
1754 [5] IEEE, "Standard Specifications for Public Key Cryptography",
1755 IEEE 1363, 2000.
1757 [6] ANSI, "Public Key Cryptography For The Financial Services
1758 Industry: The Elliptic Curve Digital Signature Algorithm
1759 (ECDSA)", ANSI X9.62, 1998.
1761 [7] NIST, "Secure Hash Standard", FIPS 180-2, 2002.
1763 [8] NIST, "Digital Signature Standard", FIPS 186-2, 2000.
1765 [9] RSA Laboratories, "PKCS#1: RSA Encryption Standard version
1766 1.5", PKCS 1, November 1993.
1768 [10] SECG, "Recommended Elliptic Curve Domain Parameters", SEC 2,
1769 2000, <http://www.secg.org/>.
1771 [11] Polk, T., Housley, R. and L. Bassham, "Algorithms and
1772 Identifiers for the Internet X.509 Public Key Infrastructure
1773 Certificate and Certificate Revocation List (CRL) Profile", RFC
1774 3279, April 2002.
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1795 Informative References
1797 [12] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key
1798 Sizes", Journal of Cryptology 14 (2001) 255-293, <http://
1799 www.cryptosavvy.com/>.
1801 [13] Freier, A., Karlton, P. and P. Kocher, "The SSL Protocol
1802 Version 3.0", November 1996, <http://wp.netscape.com/eng/ssl3/
1803 draft302.txt>.
1805 [14] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for
1806 Transport Layer Security (TLS)", RFC 3268, June 2002.
1808 [15] Hovey, R. and S. Bradner, "The Organizations Involved in the
1809 IETF Standards Process", RFC 2028, BCP 11, October 1996.
1812 Authors' Addresses
1814 Vipul Gupta
1815 Sun Microsystems Laboratories
1816 2600 Casey Avenue
1817 MS UMTV29-235
1818 Mountain View, CA 94303
1819 USA
1821 Phone: +1 650 336 1681
1822 EMail: vipul.gupta@sun.com
1825 Simon Blake-Wilson
1826 Basic Commerce & Industries, Inc.
1827 96 Spandia Ave
1828 Unit 606
1829 Toronto, ON M6G 2T6
1830 Canada
1832 Phone: +1 416 214 5961
1833 EMail: sblakewilson@bcisse.com
1836 Bodo Moeller
1837 TBD
1839 EMail: moeller@cdc.informatik.tu-darmstadt.de
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1851 Chris Hawk
1852 Independent Consultant
1854 EMail: chris@socialeng.com
1857 Nelson Bolyard
1858 Netscape
1860 EMail: misterssl@aol.com
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1907 Full Copyright Statement
1909 Copyright (C) The Internet Society (2003). All Rights Reserved.
1911 This document and translations of it may be copied and furnished to
1912 others, and derivative works that comment on or otherwise explain it
1913 or assist in its implementation may be prepared, copied, published
1914 and distributed, in whole or in part, without restriction of any
1915 kind, provided that the above copyright notice and this paragraph are
1916 included on all such copies and derivative works. However, this
1917 document itself may not be modified in any way, such as by removing
1918 the copyright notice or references to the Internet Society or other
1919 Internet organizations, except as needed for the purpose of
1920 developing Internet standards in which case the procedures for
1921 copyrights defined in the Internet Standards process must be
1922 followed, or as required to translate it into languages other than
1923 English.
1925 The limited permissions granted above are perpetual and will not be
1926 revoked by the Internet Society or its successors or assigns.
1928 This document and the information contained herein is provided on an
1929 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
1930 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
1931 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
1932 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
1933 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
1935 Acknowledgement
1937 Funding for the RFC Editor function is currently provided by the
1938 Internet Society.
1958 Gupta, et al. Expires May 1, 2004 [Page 35]
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