8 .ds RF FORMFEED[Page %]
11 .ds RH 13 September 2000
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-ke-auth-01.txt 13 September 2000
25 SILC Key Exchange and Authentication Protocols
26 <draft-riikonen-silc-ke-auth-01.txt>
31 This document is an Internet-Draft and is in full conformance with
32 all provisions of Section 10 of RFC 2026. Internet-Drafts are
33 working documents of the Internet Engineering Task Force (IETF), its
34 areas, and its working groups. Note that other groups may also
35 distribute working documents as Internet-Drafts.
37 Internet-Drafts are draft documents valid for a maximum of six months
38 and may be updated, replaced, or obsoleted by other documents at any
39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 The list of current Internet-Drafts can be accessed at
43 http://www.ietf.org/ietf/1id-abstracts.txt
45 The list of Internet-Draft Shadow Directories can be accessed at
46 http://www.ietf.org/shadow.html
48 The distribution of this memo is unlimited.
54 This memo describes two protocols used in the Secure Internet Live
55 Conferencing (SILC) protocol specified in the Secure Internet Live
56 Conferencing, Protocol Specification internet-draft [SILC1]. The
57 SILC Key Exchange (SKE) protocol provides secure key exchange between
58 two parties resulting into shared secret key material. The protocol
59 is based on Diffie Hellman key exchange algorithm and its functionality
60 is derived from several key exchange protocols. SKE uses best parts
61 of the SSH2 Key Exchange protocol, Station-To-Station (STS) protocol
62 and the OAKLEY Key Determination protocol [OAKLEY].
64 The SILC Connection Authentication protocol provides user level
65 authentication used when creating connections in SILC network. The
66 protocol is transparent to the authentication data which means that it
67 can be used to authenticate the user with, for example, passphrase
68 (pre-shared- secret) or public key (and certificate).
76 1 Introduction .................................................. 2
77 2 SILC Key Exchange Protocol .................................... 3
78 2.1 Key Exchange Payloads ..................................... 3
79 2.1.1 Key Exchange Start Payload .......................... 4
80 2.1.2 Key Exchange 1 Payload .............................. 7
81 2.1.3 Key Exchange 2 Payload .............................. 9
82 2.2 Key Exchange Procedure .................................... 10
83 2.3 Processing the Key Material ............................... 12
84 2.4 SILC Key Exchange Groups .................................. 13
85 2.4.1 diffie-hellman-group1 ............................... 13
86 2.4.2 diffie-hellman-group2 ............................... 14
87 2.5 Key Exchange Status Types ................................. 14
88 3 SILC Connection Authentication Protocol ....................... 16
89 3.1 Connection Auth Payload ................................... 17
90 3.2 Connection Authentication Types ........................... 18
91 3.2.1 Passphrase Authentication ........................... 18
92 3.2.2 Public Key Authentication ........................... 18
93 3.3 Connection Authentication Status Types .................... 19
94 4 Security Considerations ....................................... 19
95 5 References .................................................... 19
96 6 Author's Address .............................................. 20
103 Figure 1: Key Exchange Start Payload
104 Figure 2: Key Exchange 1 Payload
105 Figure 3: Key Exchange 2 Payload
106 Figure 4: Connection Auth Payload
112 This memo describes two protocols used in the Secure Internet Live
113 Conferencing (SILC) protocol specified in the Secure Internet Live
114 Conferencing, Protocol Specification internet-draft [SILC1]. The
115 SILC Key Exchange (SKE) protocol provides secure key exchange between
116 two parties resulting into shared secret key material. The protocol
117 is based on Diffie Hellman key exchange algorithm and its functionality
118 is derived from several key exchange protocols. SKE uses best parts
119 of the SSH2 Key Exchange protocol, Station-To-Station (STS) protocol
120 and the OAKLEY Key Determination protocol.
122 The SILC Connection Authentication protocol provides user level
123 authentication used when creating connections in SILC network. The
124 protocol is transparent to the authentication data which means that it
125 can be used to authenticate the user with, for example, passphrase
126 (pre-shared- secret) or public key (and certificate).
128 The basis of secure SILC session requires strong and secure key exchange
129 protocol and authentication. The authentication protocol is entirely
130 secured and no authentication data is ever sent in the network without
131 encrypting and authenticating it first. Thus, authentication protocol
132 may be used only after the key exchange protocol has been successfully
135 This document refers constantly to other SILC protocol specification
136 Internet Drafts that are a must read for those who wants to understand
137 the function of these protocols. The most important references are
138 the Secure Internet Live Conferencing, Protocol Specification [SILC1]
139 and SILC Packet Protocol [SILC2] Internet Drafts.
141 The protocol is intended to be used with the SILC protocol thus it
142 does not define own framework that could be used. The framework is
143 provided by the SILC protocol.
147 2 SILC Key Exchange Protocol
149 SILC Key Exchange Protocol (SKE) is used to exchange shared secret
150 between connecting entities. The result of this protocol is a key
151 material used to secure the communication channel. The protocol uses
152 Diffie-Hellman key exchange algorithm and its functionality is derived
153 from several key exchange protocols. SKE uses best parts of the SSH2
154 Key Exchange protocol, Station-To-Station (STS) protocol and the OAKLEY
155 Key Determination protocol. The protocol does not claim any conformance
156 to any of these protocols, they were merely used as a reference when
157 designing this protocol.
159 The purpose of SILC Key Exchange protocol is to create session keys to
160 be used in current SILC session. The keys are valid only for some period
161 of time (usually an hour) or at most until the session ends. These keys
162 are used to protect packets like commands, command replies and other
163 communication between two entities. If connection is server to server
164 connection, the keys are used to protect all traffic between those
165 servers. In client connections usually all the packets are protected
166 with this key except channel messages; channels has their own keys and
167 they are not exchanged with this protocol.
171 2.1 Key Exchange Payloads
173 During the key exchange procedure public data is sent between initiator
174 and responder. This data is later used in the key exchange procedure.
175 There are several payloads used in the key exchange. As for all SILC
176 packets, SILC Packet Header, described in [SILC2], is at the start of all
177 packets, the same is done with these payloads as well. All fields in
178 all payloads are always in MSB (most significant byte first) order.
179 Following descriptions of these payloads.
183 2.1.1 Key Exchange Start Payload
185 Key exchange between two entities always begins with a
186 SILC_PACKET_KEY_EXCHANGE packet containing Key Exchange Start Payload.
187 Initiator sends the Key Exchange Start Payload to the responder filled with
188 all security properties it supports. The responders then checks whether
189 it supports the security properties.
191 It then sends a Key Exchange Start Payload to the initiator filled with
192 security properties it selected from the original payload. The payload sent
193 by responder must include only one chosen property per list.
195 The Key Exchange Start Payload is used to tell connecting entities what
196 security properties and algorithms should be used in the communication.
197 If perfect forward secrecy (PFS) is not desired (PFS is undefined by
198 default) Key Exchange Start Payload is sent only once per session, thus,
199 for example, re-keying will not cause sending of a new payload. If PFS
200 is desired, re-keying will always cause new key exchange thus causes
201 sending of a new Key Exchange Start Payload.
203 When performing first key exchange this payload is never encrypted, as
204 there are no existing keys to encrypt it with. If performing re-keying
205 (PFS was selected) this payload is encrypted with the existing key and
206 encryption algorithm.
208 A cookie is also sent in this payload. A cookie is used to uniform the
209 payload so that none of the key exchange parties can determine this
210 payload before hand. The cookie must be returned to the original sender
213 Following diagram represents the Key Exchange Start Payload. The lists
214 mentioned below are always comma (`,') separated and the list must
215 not include spaces (` ').
226 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
228 | RESERVED | Flags | Payload Length |
229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
238 | Version String Length | |
239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
244 | Key Exchange Grp Length | |
245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
247 ~ Key Exchange Groups ~
249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
250 | PKCS Alg Length | |
251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
256 | Encryption Alg Length | |
257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
259 ~ Encryption Algorithms ~
261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
262 | Hash Alg Length | |
263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
268 | Compression Alg Length | |
269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
271 ~ Compression Algorithms ~
273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
277 Figure 1: Key Exchange Start Payload
282 o RESERVED (1 byte) - Reserved field. Sender fills this with
285 o Flags (1 byte) - Indicates flags to be used in the key
286 exchange. Several flags can be set at once by ORing the
287 flags together. Following flags are reserved for this field.
291 In this case the field is ignored.
295 If set the receiver of the payload does not reply to
300 Perfect Forward Secrecy (PFS) to be used in the
301 key exchange protocol. If not set, re-keying
302 is performed using the old key. When PFS is used,
303 re-keying and creating new keys for any particular
304 purpose will cause new key exchange.
306 Rest of the flags are reserved for the future and
309 o Payload Length (2 bytes) - Length of the entire Key Exchange
310 Start payload, not including any other field.
312 o Cookie (16 bytes) - Cookie that uniforms this payload so
313 that each of the party cannot determine the payload before
316 o Version String Length (2 bytes) - The length of the Version
317 String field, not including any other field.
319 o Version String (variable length) - Indicates the version of
320 the sender of this payload. Initiator sets this when sending
321 the payload and responder sets this when it replies by sending
322 this payload. See [SILC1] for definition of the version
325 o Key Exchange Grp Length (2 bytes) - The length of the
326 key exchange group list, not including any other field.
328 o Key Exchange Group (variable length) - The list of
329 key exchange groups. See the section 2.1.2 SILC Key Exchange
330 Groups for definitions of these groups.
332 o PKCS Alg Length (2 bytes) - The length of the PKCS algorithms
333 list, not including any other field.
335 o PKCS Algorithms (variable length) - The list of PKCS
338 o Encryption Alg Length (2 bytes) - The length of the encryption
339 algorithms list, not including any other field.
341 o Encryption Algorithms (variable length) - The list of
342 encryption algorithms.
344 o Hash Alg Length (2 bytes) - The length of the Hash algorithms
345 list, not including any other field.
347 o Hash Algorithms (variable length) - The list of Hash algorithms.
349 o Compression Alg Length (2 bytes) - The length of the
350 compression algorithms list, not including any other field.
352 o Compression Algorithms (variable length) - The list of
353 compression algorithms.
358 2.1.2 Key Exchange 1 Payload
360 Key Exchange 1 Payload is used to deliver computed public data from
361 initiator to responder. This data is used to compute the shared secret,
362 later by all parties. Key Exchange 1 Payload is only sent after the
363 SILC_PACKET_KEY_EXCHANGE packet and the Key Exchange Start Payload has
364 been processed by all the parties.
366 This payload sends the initiator's public key to the responder. Responder
367 may need the public key in which case it should be checked to be trusted
370 The payload may only be sent with SILC_PACKET_KEY_EXCHANGE_1 packet.
371 It must not be sent in any other packet type. Following diagram
372 represent the Key Exchange 1 Payload.
392 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
394 | Public Key Length | Public Key Type |
395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
397 ~ Public Key of the Host (or certificate) ~
399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
400 | Public Data Length | |
401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
403 ~ Public Data (e = g ^ x mod p) ~
405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
409 Figure 2: Key Exchange 1 Payload
413 o Public Key Length (2 bytes) - The length of the Public Key
414 (or certificate) field, not including any other field.
416 o Public Key Type (2 bytes) - The public key (or certificate)
417 type. This field indicates the type of the public key in
418 the packet. Following types are defined:
420 1 SILC style public key (mandatory)
421 2 SSH2 style public key (optional)
422 3 X.509 Version 3 certificate (optional)
423 4 OpenPGP certificate (optional)
424 5 SPKI certificate (optional)
426 The only required type to support is type number 1. See
427 [SILC1] for the SILC public key specification. See
428 SSH public key specification in [SSH-TRANS]. See X.509v3
429 certificate specification in [PKIX-Part1]. See OpenPGP
430 certificate specification in [PGP]. See SPKI certificate
431 specification in [SPKI]. If this field includes zero (0)
432 or unsupported type number the protocol must be aborted
433 sending SILC_PACKET_FAILURE message.
435 o Public Data Length (2 bytes) - The length of the public
436 data computed by the responder, not including any other
439 o Public Data (variable length) - The public data to be
440 sent to the responder. See section 2.2 Key Exchange
441 Procedure for detailed description how this field is
442 computed. This value is binary encoded.
447 2.1.3 Key Exchange 2 Payload
449 Key Exchange 2 Payload is used to deliver public key, computed public
450 data and signature from responder to initiator. Initiator uses these
451 public parts of the key exchange protocol to compute the shared secret.
453 The payload may only be sent with SILC_PACKET_KEY_EXCHANGE_2 packet.
454 It must not be sent in any other packet type. Following diagram
455 represent the Key Exchange 2 Payload.
462 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
464 | Public Key Length | Public Key Type |
465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
467 ~ Public Key of the Host (or certificate) ~
469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
470 | Public Data Length | |
471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
473 ~ Public Data (f = g ^ y mod p) ~
475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
476 | Signature Length | |
477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
485 Figure 3: Key Exchange 2 Payload
490 o Public Key Length (2 bytes) - The length of the Public Key
491 (or certificate) field, not including any other field.
493 o Public Key Type (2 bytes) - The public key (or certificate)
494 type. This field indicates the type of the public key in
495 the packet. See previous sections for defined public key
498 o Public Key of the host (variable length) - The public
499 key of the sender (or its certificate). This is verified
500 by the receiver of the packet. The type of this field
501 is indicated by previous Public Key Type field.
503 o Public Data Length (2 bytes) - The length of the public
504 data computed by the responder, not including any other
507 o Public Data (variable length) - The public data computed
508 by the responder. See section 2.2 Key Exchange Procedure
509 for detailed description how this field is computed. This
510 value is binary encoded.
512 o Signature Length (2 bytes) - The length of the signature,
513 not including any other field.
515 o Signature Data (variable length) - The signature signed
516 by the responder. The receiver of this signature must
517 verify it. The verification is done using the public
518 key received in this same payload. See section 2.2
519 Key Exchange Procedure for detailed description how
520 to produce the signature.
524 2.2 Key Exchange Procedure
526 The key exchange begins by sending SILC_PACKET_KEY_EXCHANGE packet with
527 Key Exchange Start Payload to select the security properties to be used
528 in the key exchange and later in the communication.
530 After Key Exchange Start Payload has been processed by both of the
531 parties the protocol proceeds as follows:
534 Setup: p is a large and public safe prime. This is one of the
535 Diffie Hellman groups. q is order of subgroup (largest
536 prime factor of p). g is a generator and is defined
537 along with the Diffie Hellman group.
539 1. Initiator generates a random number x, where 1 < x < q,
540 and computes e = g ^ x mod p. The result e is then
541 encoded into Key Exchange 1 Payload and sent
545 2. Responder generates a random number y, where 1 < y < q,
546 and computes f = g ^ y mod p. It then computes the
547 shared secret KEY = e ^ y mod p, and, a hash value
548 HASH = hash(Key Exchange Start Payload data | Host public
549 key (or certificate) | e | f | KEY). It then signs
550 the HASH value with its private key resulting a signature
553 It then encodes its public key (or certificate), f and
554 SIGN into Key Exchange 2 Payload and sends it to the
558 3. Initiator verifies that the public key provided in
559 the payload is authentic, or if certificates are used
560 it verifies the certificate. Initiator may accept
561 the public key without verifying it, however, doing
562 so may result to insecure key exchange (accepting the
563 public key without verifying may be desirable for
564 practical reasons on many environments. For long term
565 use this is never desirable, in which case certificates
566 would be the preferred method to use).
568 Initiator then computes the shared secret KEY =
569 f ^ x mod p, and, a hash value HASH in the same way as
570 responder did in phase 2. It then verifies the
571 signature SIGN from the payload with the hash value
572 HASH using the received public key.
575 If any of these phases is to fail SILC_PACKET_FAILURE is sent to
576 indicate that the key exchange protocol failed. Any other packets must
577 not be sent or accepted during the key exchange except the
578 SILC_PACKET_KEY_EXCHANGE_*, SILC_PACKET_DISCONNECT, SILC_PACKET_FAILURE
579 and/or SILC_PACKET_SUCCESS packets.
581 The result of this protocol is a shared secret key material KEY and
582 a hash value HASH. The key material itself is not fit to be used as
583 a key, it needs to be processed further to derive the actual keys to be
584 used. The key material is also used to produce other security parameters
585 later used in the communication. See section 2.3 Processing the Key
586 Material for detailed description how to process the key material.
588 After the keys are processed the protocol is ended by sending the
589 SILC_PACKET_SUCCESS packet. Both entities send this packet to
590 each other. After this both parties will start using the new keys.
595 2.3 Processing the Key Material
597 Key Exchange protocol produces secret shared key material KEY. This
598 key material is used to derive the actual keys used in the encryption
599 of the communication channel. The key material is also used to derive
600 other security parameters used in the communication. Key Exchange
601 protocol produces a hash value HASH as well. This is used in the key
602 deriving process as a session identifier.
604 Keys are derived from the key material as follows:
607 Sending Initial Vector (IV) = hash(0 | KEY | HASH)
608 Receiving Initial Vector (IV) = hash(1 | KEY | HASH)
609 Sending Encryption Key = hash(2 | KEY | HASH)
610 Receiving Encryption Key = hash(3 | KEY | HASH)
611 HMAC Key = hash(4 | KEY | HASH)
615 The Initial Vector (IV) is used in the encryption when doing for
616 example CBC mode. As many bytes as needed are taken from the start of
617 the hash output for IV. Sending IV is for sending key and receiving IV
618 is for receiving key. For receiving party, the receiving IV is actually
619 sender's sending IV, and, the sending IV is actually sender's receiving
620 IV. Initiator uses IV's as they are (sending IV for sending and
621 receiving IV for receiving).
623 The Encryption Keys are derived as well from the hash(). If the hash()
624 output is too short for the encryption algorithm more key material is
625 produced in following manner:
628 K1 = hash(2 | KEY | HASH)
630 K3 = hash(KEY | K1 | K2) ...
632 Sending Encryption Key = K1 | K2 | K3 ...
635 K1 = hash(3 | KEY | HASH)
637 K3 = hash(KEY | K1 | K2) ...
639 Receiving Encryption Key = K1 | K2 | K3 ...
643 The key is distributed by hashing the previous hash with the original
644 key material. The final key is a concatenation of the hash values.
645 For Receiving Encryption Key the procedure is equivalent. Sending key
646 is used only for encrypting data to be sent. The receiving key is used
647 only to decrypt received data. For receiving party, the receive key is
648 actually sender's sending key, and, the sending key is actually sender's
649 receiving key. Initiator uses generated keys as they are (sending key
650 for sending and receiving key for sending).
652 The HMAC key is used to create MAC values to packets in the communication
653 channel. As many bytes as needed are taken from the start of the hash
656 These procedures are performed by all parties of the key exchange
657 protocol. This must be done before the protocol has been ended by
658 sending the SILC_PACKET_SUCCESS packet.
662 2.4 SILC Key Exchange Groups
664 Following groups may be used in the SILC Key Exchange protocol. The
665 first group diffie-hellman-group1 is mandatory, other groups maybe
666 negotiated to be used in the connection with Key Exchange Start Payload
667 and SILC_PACKET_KEY_EXCHANGE packet. However, the first group must be
668 proposed in the Key Exchange Start Payload regardless of any other
669 requested group (however, it does not have to be the first on the list).
673 2.4.1 diffie-hellman-group1
675 The length of this group is 1024 bits. This is mandatory group.
676 The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
681 179769313486231590770839156793787453197860296048756011706444
682 423684197180216158519368947833795864925541502180565485980503
683 646440548199239100050792877003355816639229553136239076508735
684 759914822574862575007425302077447712589550957937778424442426
685 617334727629299387668709205606050270810842907692932019128194
689 Its hexadecimal value is
692 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
693 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
694 EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
695 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
696 EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
701 The generator used with this prime is g = 2. The group order q is
704 This group was taken from the OAKLEY specification.
708 2.4.2 diffie-hellman-group2
710 The length of this group is 1536 bits. This is optional group.
711 The prime is 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }.
716 241031242692103258855207602219756607485695054850245994265411
717 694195810883168261222889009385826134161467322714147790401219
718 650364895705058263194273070680500922306273474534107340669624
719 601458936165977404102716924945320037872943417032584377865919
720 814376319377685986952408894019557734611984354530154704374720
721 774996976375008430892633929555996888245787241299381012913029
722 459299994792636526405928464720973038494721168143446471443848
723 8520940127459844288859336526896320919633919
726 Its hexadecimal value is
729 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
730 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
731 EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
732 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
733 EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
734 C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
735 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
736 670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF
739 The generator used with this prime is g = 2. The group order q is
742 This group was taken from the OAKLEY specification.
746 2.5 Key Exchange Status Types
748 This section defines all key exchange protocol status types that may be
749 returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets to
750 indicate the status of the protocol. Implementations may map the
751 status types to human readable error message. All types except the
752 SILC_SKE_STATUS_OK type must be sent in SILC_PACKET_FAILURE packet.
753 Following status types are defined:
758 Protocol were exeucted succesfully.
761 1 SILC_SKE_STATUS_ERROR
763 Unknown error occured. No specific error type is defined.
766 2 SILC_SKE_STATUS_BAD_PAYLOAD
768 Provided KE payload were malformed or included bad fields.
771 3 SILC_SKE_STATUS_UNSUPPORTED_GROUP
773 None of the provided groups were supported.
776 4 SILC_SKE_STATUS_UNSUPPORTED_CIPHER
778 None of the provided ciphers were supported.
781 5 SILC_SKE_STATUS_UNSUPPORTED_PKCS
783 None of the provided public key algorithms were supported.
786 6 SILC_SKE_STATUS_UNSUPPORTED_HASH_FUNCTION
788 None of the provided hash functions were supported.
791 7 SILC_SKE_STATUS_UNSUPPORTED_PUBLIC_KEY
793 Provided public key type is not supported.
796 8 SILC_SKE_STATUS_INCORRECT_SIGNATURE
798 Provided signature was incorrect.
806 3 SILC Connection Authentication Protocol
808 Purpose of Connection Authentication protocol is to authenticate the
809 connecting party with server. Usually connecting party is client but
810 server may connect to server as well. Its other purpose is to provide
811 information for the server about which type of connection this is.
812 The type defines whether this is client, server or router connection.
813 Server uses this information to create the ID for the connection. After
814 the authentication protocol has been successfully completed
815 SILC_PACKET_NEW_ID must be sent to the connecting party by the server.
816 See section New ID Payload in [SILC2] for detailed description for this
819 Server must verify the authentication data received and if it is to fail
820 the authentication must be failed by sending SILC_PACKET_FAILURE packet.
821 If everything checks out fine the protocol is ended by server by sending
822 SILC_PACKET_SUCCESS packet.
824 The protocol is executed after the SILC Key Exchange protocol. It must
825 not be executed in any other time. As it is performed after key exchange
826 protocol all traffic in the connection authentication protocol is
827 encrypted with the exchanged keys.
829 The protocol is started by the connecting party by sending
830 SILC_PACKET_CONNECTION_AUTH packet with Connection Auth Payload,
831 described in the next section. This payload must include the
832 authentication data. Authentication data is set according
833 authentication method that must be known by both parties. If connecting
834 party does not know what is the mandatory authentication method it must
835 request it from the server by sending SILC_PACKET_CONNECTION_AUTH_REQUEST
836 packet. This packet is not part of this protocol and is described in
837 section Connection Auth Request Payload in [SILC2]. However, if
838 connecting party already knows the mandatory authentication method
839 sending the request is not necessary.
841 See [SILC1] and section Connection Auth Request Payload in [SILC2] also
842 for the list of different authentication methods. Authentication method
843 may also be NONE, in which case the server does not require
844 authentication at all. However, in this case the protocol still must be
845 executed; the authentication data just is empty indicating no
846 authentication is required.
848 If authentication method is passphrase the authentication data is
849 plaintext passphrase. As the payload is entirely encrypted it is safe
850 to have plaintext passphrase. 3.2.1 Passphrase Authentication for
854 If authentication method is public key authentication the authentication
855 data is signature of the hash value HASH plus Key Exchange Start Payload,
856 established by the SILC Key Exchange protocol. This signature must then
857 be verified by the server. See section 3.2.2 Public Key Authentication
858 for more information.
860 The connecting party of this protocol must wait after successful execution
861 of this protocol for the SILC_PACKET_NEW_ID packet where it will receive
862 the ID it will be using in the SILC network. Connecting party cannot
863 start normal SILC session (sending messages or commands) until it has
864 received its ID. The ID's are always created by the server except
865 for server to server connection where servers create their own ID's.
870 3.1 Connection Auth Payload
872 Client sends this payload to authenticate itself to the server. Server
873 connecting to another server also sends this payload. Server receiving
874 this payload must verify all the data in it and if something is to fail
875 the authentication must be failed by sending SILC_PACKET_FAILURE packet.
877 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH packet.
878 It must not be sent in any other packet type. Following diagram
879 represent the Connection Auth Payload.
885 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
887 | Payload Length | Connection Type |
888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
890 ~ Authentication Data ~
892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
896 Figure 4: Connection Auth Payload
900 o Payload Length (2 bytes) - Length of the entire Connection
903 o Connection Type (2 bytes) - Indicates the type of the
904 connection. See section Connection Auth Request Payload
905 in [SILC2] for the list of connection types. This field must
906 include valid connection type or the packet must be discarded
907 and authentication must be failed.
909 o Authentication Data (variable length) - The actual
910 authentication data. Contents of this depends on the
911 authentication method known by both parties. If no
912 authentication is required this field does not exist.
917 3.2 Connection Authentication Types
919 SILC supports two authentication types to be used in the connection
920 authentication protocol; passphrase or public key based authentication.
921 Following sections defines the authentication methods. See [SILC2]
922 for defined numerical authentication method types.
926 3.2.1 Passphrase Authentication
928 Passphrase authentication or pre-shared-key base authentication is
929 simply an authentication where the party that wants to authenticate
930 itself to the other end sends the passphrase that is required by
931 the other end, for example server.
933 If the passphrase matches with the one in the server's end the
934 authentication is successful. Otherwise SILC_PACKET_FAILURE must be
935 sent to the sender and the protocol execution fails.
937 This is required authentication method to be supported by all SILC
942 3.2.2 Public Key Authentication
944 Public key authentication may be used if passphrase based authentication
945 is not desired. The public key authentication works by sending a
946 signature as authentication data to the other end, say, server. The
947 server must then verify the signature by the public key of the sender,
948 which the server has received earlier in SKE protocol.
950 The signature is computed using the private key of the sender by signing
951 the HASH value provided by the SKE protocol previously, and the Key
952 Exchange Start Payload from SKE protocol that was sent to the server.
953 The server must verify the data, thus it must keep the HASH and the
954 Key Exchange Start Payload saved during SKE and authentication protocols.
956 If the verified signature matches the sent signature, the authentication
957 were successful and SILC_PACKET_SUCCESS is sent. If it failed the protocol
958 execution is stopped and SILC_PACKET_FAILURE is sent.
960 This is required authentication method to be supported by all SILC
965 3.3 Connection Authentication Status Types
967 This section defines all connection authentication status types that
968 may be returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets
969 to indicate the status of the protocol. Implementations may map the
970 status types to human readable error message. All types except the
971 SILC_AUTH_STATUS_OK type must be sent in SILC_PACKET_FAILURE packet.
972 Following status types are defined:
976 Protocol was executed succesfully.
981 Authentication failed.
985 4 Security Considerations
987 Security is central to the design of this protocol, and these security
988 considerations permeate the specification.
994 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
995 Protocol Specification", Internet Draft, June 2000.
997 [SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
1000 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
1003 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
1006 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
1009 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
1012 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
1013 Infrastructure, Certificate and CRL Profile", RFC 2459,
1016 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
1017 John Wiley & Sons, New York, NY, 1996.
1019 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
1022 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
1023 RFC 2412, November 1998.
1025 [ISAKMP] Maughan D., et al, "Internet Security Association and
1026 Key Management Protocol (ISAKMP)", RFC 2408, November
1029 [IKE] Harkins D., and Carrel D., "The Internet Key Exhange
1030 (IKE)", RFC 2409, November 1998.
1032 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
1033 Authentication", RFC 2104, February 1997.
1045 EMail: priikone@poseidon.pspt.fi
1047 This Internet-Draft expires 13 May 2001