8 .ds RF FORMFEED[Page %]
17 Network Working Group P. Riikonen
19 draft-riikonen-silc-ke-auth-02.txt XXXXXXXXXXXXXX
25 SILC Key Exchange and Authentication Protocols
26 <draft-riikonen-silc-ke-auth-02.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
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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
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45 The list of Internet-Draft Shadow Directories can be accessed at
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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 Payload ................................ 7
81 2.2 Key Exchange Procedure .................................... 10
82 2.3 Processing the Key Material ............................... 12
83 2.4 SILC Key Exchange Groups .................................. 13
84 2.4.1 diffie-hellman-group1 ............................... 13
85 2.4.2 diffie-hellman-group2 ............................... 14
86 2.5 Key Exchange Status Types ................................. 14
87 3 SILC Connection Authentication Protocol ....................... 16
88 3.1 Connection Auth Payload ................................... 17
89 3.2 Connection Authentication Types ........................... 18
90 3.2.1 Passphrase Authentication ........................... 18
91 3.2.2 Public Key Authentication ........................... 18
92 3.3 Connection Authentication Status Types .................... 19
93 4 Security Considerations ....................................... 19
94 5 References .................................................... 19
95 6 Author's Address .............................................. 20
102 Figure 1: Key Exchange Start Payload
103 Figure 2: Key Exchange Payload
104 Figure 3: Connection Auth Payload
110 This memo describes two protocols used in the Secure Internet Live
111 Conferencing (SILC) protocol specified in the Secure Internet Live
112 Conferencing, Protocol Specification Internet-Draft [SILC1]. The
113 SILC Key Exchange (SKE) protocol provides secure key exchange between
114 two parties resulting into shared secret key material. The protocol
115 is based on Diffie Hellman key exchange algorithm and its functionality
116 is derived from several key exchange protocols. SKE uses best parts
117 of the SSH2 Key Exchange protocol, Station-To-Station (STS) protocol
118 and the OAKLEY Key Determination protocol.
120 The SILC Connection Authentication protocol provides user level
121 authentication used when creating connections in SILC network. The
122 protocol is transparent to the authentication data which means that it
123 can be used to authenticate the user with, for example, passphrase
124 (pre-shared- secret) or public key (and certificate).
126 The basis of secure SILC session requires strong and secure key exchange
127 protocol and authentication. The authentication protocol is entirely
128 secured and no authentication data is ever sent in the network without
129 encrypting and authenticating it first. Thus, authentication protocol
130 may be used only after the key exchange protocol has been successfully
133 This document refers constantly to other SILC protocol specification
134 Internet Drafts that are a must read for those who wants to understand
135 the function of these protocols. The most important references are
136 the Secure Internet Live Conferencing, Protocol Specification [SILC1]
137 and the SILC Packet Protocol [SILC2] Internet Drafts.
139 The protocol is intended to be used with the SILC protocol thus it
140 does not define own framework that could be used. The framework is
141 provided by the SILC protocol.
145 2 SILC Key Exchange Protocol
147 SILC Key Exchange Protocol (SKE) is used to exchange shared secret
148 between connecting entities. The result of this protocol is a key
149 material used to secure the communication channel. The protocol uses
150 Diffie-Hellman key exchange algorithm and its functionality is derived
151 from several key exchange protocols. SKE uses best parts of the SSH2
152 Key Exchange protocol, Station-To-Station (STS) protocol and the OAKLEY
153 Key Determination protocol. The protocol does not claim any conformance
154 to any of these protocols, they were merely used as a reference when
155 designing this protocol.
157 The purpose of SILC Key Exchange protocol is to create session keys to
158 be used in current SILC session. The keys are valid only for some period
159 of time (usually an hour) or at most until the session ends. These keys
160 are used to protect packets like commands, command replies and other
161 communication between two entities. If connection is server to router
162 connection, the keys are used to protect all traffic between those
163 servers. In client connections usually all the packets are protected
164 with this key except channel messages; channels has their own keys and
165 they are not exchanged with this protocol.
167 The Diffie-Hellman implementation used in the SILC should be compliant
172 2.1 Key Exchange Payloads
174 During the key exchange procedure public data is sent between initiator
175 and responder. This data is later used in the key exchange procedure.
176 There are several payloads used in the key exchange. As for all SILC
177 packets, SILC Packet Header, described in [SILC2], is at the start of all
178 packets, the same is done with these payloads as well. All fields in
179 all payloads are always in MSB (most significant byte first) order.
180 Following descriptions of these payloads.
184 2.1.1 Key Exchange Start Payload
186 Key exchange between two entities always begins with the
187 SILC_PACKET_KEY_EXCHANGE packet containing Key Exchange Start Payload.
188 Initiator sends the Key Exchange Start Payload to the responder filled with
189 all security properties it supports. The responders then checks whether
190 it supports the security properties.
192 It then sends a Key Exchange Start Payload to the initiator filled with
193 security properties it selected from the original payload. The payload sent
194 by responder must include only one chosen property per list.
196 The Key Exchange Start Payload is used to tell connecting entities what
197 security properties and algorithms should be used in the communication.
198 The Key Exchange Start Payload is sent only once per session. Even if
199 the PFS (Perfect Forward Secrecy) flag is se the Key Exchange Start Payload
200 is not re-sent. When PFS is desired the Key Exchange Payloads are sent
201 to negotiate new key material. The procedure is equivalent to the very
202 first negotiation except that the Key Exchange Start Payload is not sent.
204 As this payload is used only with the very first key exchnage the payload
205 is never encrypted, as there are no keys to encrypt it with.
207 A cookie is also sent in this payload. A cookie is used to uniform the
208 payload so that none of the key exchange parties can determine this
209 payload before hand. The cookie must be returned to the original sender
212 Following diagram represents the Key Exchange Start Payload. The lists
213 mentioned below are always comma (`,') separated and the list must
214 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
274 | Compression Alg Length | |
275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
277 ~ Compression Algorithms ~
279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
283 Figure 1: Key Exchange Start Payload
288 o RESERVED (1 byte) - Reserved field. Sender fills this with
291 o Flags (1 byte) - Indicates flags to be used in the key
292 exchange. Several flags can be set at once by ORing the
293 flags together. Following flags are reserved for this field.
297 In this case the field is ignored.
301 If set the receiver of the payload does not reply to
306 Perfect Forward Secrecy (PFS) to be used in the
307 key exchange protocol. If not set, re-keying
308 is performed using the old key. See the [SILC1]
309 for more information on this issue. When PFS is used,
310 re-keying and creating new keys for any particular
311 purpose will cause new key exchange. In this key
312 exchange only the Key Exchange Payload is sent and
313 the Key Exchange Start Payload must not be sent.
314 When doing PFS the Key Exchange Payloads are
315 encrypted with the old keys. With the PFS, the
316 Mutual Authentication flag must be ignored.
318 Mutual Authentication 0x04
320 Both of the parties will perform authenetication
321 by providing signed data for the other party to
322 verify. By default, only responder will provide
323 the signature data. If this is set then the
324 inititator must also provide it. Initiator may
325 set this but also responder may set this even if
326 initiator did not set it.
328 Rest of the flags are reserved for the future and
331 o Payload Length (2 bytes) - Length of the entire Key Exchange
332 Start payload, not including any other field.
334 o Cookie (16 bytes) - Cookie that uniforms this payload so
335 that each of the party cannot determine the payload before
338 o Version String Length (2 bytes) - The length of the Version
339 String field, not including any other field.
341 o Version String (variable length) - Indicates the version of
342 the sender of this payload. Initiator sets this when sending
343 the payload and responder sets this when it replies by sending
344 this payload. See [SILC1] for definition of the version
347 o Key Exchange Grp Length (2 bytes) - The length of the
348 key exchange group list, not including any other field.
350 o Key Exchange Group (variable length) - The list of
351 key exchange groups. See the section 2.1.2 SILC Key Exchange
352 Groups for definitions of these groups.
354 o PKCS Alg Length (2 bytes) - The length of the PKCS algorithms
355 list, not including any other field.
357 o PKCS Algorithms (variable length) - The list of PKCS
360 o Encryption Alg Length (2 bytes) - The length of the encryption
361 algorithms list, not including any other field.
363 o Encryption Algorithms (variable length) - The list of
364 encryption algorithms.
366 o Hash Alg Length (2 bytes) - The length of the Hash algorithm
367 list, not including any other field.
369 o Hash Algorithms (variable length) - The list of Hash
370 algorithms. The hash algorithms are mainly used in the
373 o HMAC Length (2 bytes) - The length of the HMAC list, not
374 including any other field.
376 o HMACs (variable length) - The list of HMACs. The HMAC's
377 are used to compute the Message Authentication Codes (MAC)
380 o Compression Alg Length (2 bytes) - The length of the
381 compression algorithms list, not including any other field.
383 o Compression Algorithms (variable length) - The list of
384 compression algorithms.
389 2.1.2 Key Exchange Payload
391 Key Exchange payload is used to deliver the public key (or certificate),
392 the computed Diffie-Hellman public value and possibly signature data
393 from one party to the other. When initiator is using this payload
394 and the Mutual Authentication flag is not set then the initiator must
395 not provide the signature data. If the flag is set then the initiator
396 must provide the signature data so that the responder may verify it.
398 The Mutual Authentication flag is usually used only if a separate
399 authentication protocol will not be executed for the initiator of the
400 prtocool. This is case for example when the SKE is performed between
401 two SILC clients. In normal case, where client is connecting to the
402 server or server is connecting to the router the Mutual Authentication
403 flag is not necessary.
405 This payload is sent inside SILC_PACKET_KEY_EXCHANGE_1 and inside
406 SILC_PACKET_KEY_EXCHANGE_2 packet types. The initiator uses the
407 SILC_PACKET_KEY_EXCHANGE_1 and the responder the latter.
409 The following diagram represent the Key Exchange 1 Payload.
415 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
416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
417 | Public Key Length | Public Key Type |
418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
420 ~ Public Key of the party (or certificate) ~
422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
423 | Public Data Length | |
424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
429 | Signature Length | |
430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
438 Figure 2: Key Exchange Payload
442 o Public Key Length (2 bytes) - The length of the Public Key
443 (or certificate) field, not including any other field.
445 o Public Key Type (2 bytes) - The public key (or certificate)
446 type. This field indicates the type of the public key in
447 the packet. Following types are defined:
449 1 SILC style public key (mandatory)
450 2 SSH2 style public key (optional)
451 3 X.509 Version 3 certificate (optional)
452 4 OpenPGP certificate (optional)
453 5 SPKI certificate (optional)
455 The only required type to support is type number 1. See
456 [SILC1] for the SILC public key specification. See
457 SSH public key specification in [SSH-TRANS]. See X.509v3
458 certificate specification in [PKIX-Part1]. See OpenPGP
459 certificate specification in [PGP]. See SPKI certificate
460 specification in [SPKI]. If this field includes zero (0)
461 or unsupported type number the protocol must be aborted
462 sending SILC_PACKET_FAILURE message and the connection should
463 be closed immediately.
465 o Public Data Length (2 bytes) - The length of the Public Data
466 field, not including any other field.
468 o Public Data (variable length) - The public data to be
469 sent to the receiver. See section 2.2 Key Exchange
470 Procedure for detailed description how this field is
471 computed. This value is binary encoded.
473 o Signature Length (2 bytes) - The length of the signature,
474 not including any other field.
476 o Signature Data (variable length) - The signature signed
477 by the sender. The receiver of this signature must
478 verify it. The verification is done using the public
479 key received in this same payload. See section 2.2
480 Key Exchange Procedure for detailed description how
481 to produce the signature. If the Mutual Authentication
482 flag is not set then initiator must not provide this
483 field and the Signature Length field must be set to zero (0)
484 value. If the flag is set then also the initiator must
485 provide this field. The responder always provides this
491 2.2 Key Exchange Procedure
493 The key exchange begins by sending SILC_PACKET_KEY_EXCHANGE packet with
494 Key Exchange Start Payload to select the security properties to be used
495 in the key exchange and later in the communication.
497 After Key Exchange Start Payload has been processed by both of the
498 parties the protocol proceeds as follows:
501 Setup: p is a large and public safe prime. This is one of the
502 Diffie Hellman groups. q is order of subgroup (largest
503 prime factor of p). g is a generator and is defined
504 along with the Diffie Hellman group.
506 1. Initiator generates a random number x, where 1 < x < q,
507 and computes e = g ^ x mod p. The result e is then
508 encoded into Key Exchange Payload and sent to the
511 If the Mutual Authentication flag is set then initiator
512 must also produce signature data SIGN_i which the responder
513 will verify. The initiator must compute a hash value
514 HASH_i = hash(Key Exchange Start Payload | public key
515 (or certificate) | e). It then signs the HASH_i value with
516 its private key resulting a signature SIGN_i.
518 2. Responder generates a random number y, where 1 < y < q,
519 and computes f = g ^ y mod p. It then computes the
520 shared secret KEY = e ^ y mod p, and, a hash value
521 HASH = hash(Key Exchange Start Payload data | public
522 key (or certificate) | e | f | KEY). It then signs
523 the HASH value with its private key resulting a signature
526 It then encodes its public key (or certificate), f and
527 SIGN into Key Exchange Payload and sends it to the
530 If the Mutual Authentication flag is set then the responder
531 should verify that the public key provided in the payload
532 is authentic, or if certificates are used it verifies the
533 certificate. The responder may accept the public key without
534 verifying it, however, doing so may result to insecure key
535 exchange (accepting the public key without verifying may be
536 desirable for practical reasons on many environments. For
537 long term use this is never desirable, in which case
538 certificates would be the preferred method to use). It then
539 computes the HASH_i value the same way initiator did in the
540 phase 1. It then verifies the signature SIGN_i from the
541 payload with the hash value HASH_i using the received public
544 3. Initiator verifies that the public key provided in
545 the payload is authentic, or if certificates are used
546 it verifies the certificate. The initiator may accept
547 the public key without verifying it, however, doing
548 so may result to insecure key exchange (accepting the
549 public key without verifying may be desirable for
550 practical reasons on many environments. For long term
551 use this is never desirable, in which case certificates
552 would be the preferred method to use).
554 Initiator then computes the shared secret KEY =
555 f ^ x mod p, and, a hash value HASH in the same way as
556 responder did in phase 2. It then verifies the
557 signature SIGN from the payload with the hash value
558 HASH using the received public key.
561 If any of these phases is to fail SILC_PACKET_FAILURE is sent to
562 indicate that the key exchange protocol has failed, and the connection
563 should be closed immediately. Any other packets must not be sent or
564 accepted during the key exchange except the SILC_PACKET_KEY_EXCHANGE_*,
565 SILC_PACKET_FAILURE and SILC_PACKET_SUCCESS packets.
567 The result of this protocol is a shared secret key material KEY and
568 a hash value HASH. The key material itself is not fit to be used as
569 a key, it needs to be processed further to derive the actual keys to be
570 used. The key material is also used to produce other security parameters
571 later used in the communication. See section 2.3 Processing the Key
572 Material for detailed description how to process the key material.
574 If the Mutual Authentication flag was set the protocol produces also
575 a hash value HASH_i. This value, however, must be discarded.
577 After the keys are processed the protocol is ended by sending the
578 SILC_PACKET_SUCCESS packet. Both entities send this packet to
579 each other. After this both parties will start using the new keys.
585 2.3 Processing the Key Material
587 Key Exchange protocol produces secret shared key material KEY. This
588 key material is used to derive the actual keys used in the encryption
589 of the communication channel. The key material is also used to derive
590 other security parameters used in the communication. Key Exchange
591 protocol produces a hash value HASH as well.
593 Keys are derived from the key material as follows:
596 Sending Initial Vector (IV) = hash(0 | KEY | HASH)
597 Receiving Initial Vector (IV) = hash(1 | KEY | HASH)
598 Sending Encryption Key = hash(2 | KEY | HASH)
599 Receiving Encryption Key = hash(3 | KEY | HASH)
600 HMAC Key = hash(4 | KEY | HASH)
604 The Initial Vector (IV) is used in the encryption when doing for
605 example CBC mode. As many bytes as needed are taken from the start of
606 the hash output for IV. Sending IV is for sending key and receiving IV
607 is for receiving key. For receiving party, the receiving IV is actually
608 sender's sending IV, and, the sending IV is actually sender's receiving
609 IV. Initiator uses IV's as they are (sending IV for sending and
610 receiving IV for receiving).
612 The Encryption Keys are derived as well from the hash(). If the hash()
613 output is too short for the encryption algorithm more key material is
614 produced in following manner:
617 K1 = hash(2 | KEY | HASH)
619 K3 = hash(KEY | K1 | K2) ...
621 Sending Encryption Key = K1 | K2 | K3 ...
624 K1 = hash(3 | KEY | HASH)
626 K3 = hash(KEY | K1 | K2) ...
628 Receiving Encryption Key = K1 | K2 | K3 ...
632 The key is distributed by hashing the previous hash with the original
633 key material. The final key is a concatenation of the hash values.
634 For Receiving Encryption Key the procedure is equivalent. Sending key
635 is used only for encrypting data to be sent. The receiving key is used
636 only to decrypt received data. For receiving party, the receive key is
637 actually sender's sending key, and, the sending key is actually sender's
638 receiving key. Initiator uses generated keys as they are (sending key
639 for sending and receiving key for sending).
641 The HMAC key is used to create MAC values to packets in the communication
642 channel. As many bytes as needed are taken from the start of the hash
645 These procedures are performed by all parties of the key exchange
646 protocol. This must be done before the protocol has been ended by
647 sending the SILC_PACKET_SUCCESS packet.
651 2.4 SILC Key Exchange Groups
653 Following groups may be used in the SILC Key Exchange protocol. The
654 first group diffie-hellman-group1 is mandatory, other groups maybe
655 negotiated to be used in the connection with Key Exchange Start Payload
656 and SILC_PACKET_KEY_EXCHANGE packet. However, the first group must be
657 proposed in the Key Exchange Start Payload regardless of any other
658 requested group (however, it does not have to be the first in the list).
662 2.4.1 diffie-hellman-group1
664 The length of this group is 1024 bits. This is mandatory group.
665 The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
670 179769313486231590770839156793787453197860296048756011706444
671 423684197180216158519368947833795864925541502180565485980503
672 646440548199239100050792877003355816639229553136239076508735
673 759914822574862575007425302077447712589550957937778424442426
674 617334727629299387668709205606050270810842907692932019128194
678 Its hexadecimal value is
681 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
682 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
683 EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
684 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
685 EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
690 The generator used with this prime is g = 2. The group order q is
693 This group was taken from the OAKLEY specification.
697 2.4.2 diffie-hellman-group2
699 The length of this group is 1536 bits. This is optional group.
700 The prime is 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }.
705 241031242692103258855207602219756607485695054850245994265411
706 694195810883168261222889009385826134161467322714147790401219
707 650364895705058263194273070680500922306273474534107340669624
708 601458936165977404102716924945320037872943417032584377865919
709 814376319377685986952408894019557734611984354530154704374720
710 774996976375008430892633929555996888245787241299381012913029
711 459299994792636526405928464720973038494721168143446471443848
712 8520940127459844288859336526896320919633919
715 Its hexadecimal value is
718 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
719 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
720 EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
721 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
722 EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
723 C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
724 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
725 670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF
728 The generator used with this prime is g = 2. The group order q is
731 This group was taken from the OAKLEY specification.
735 2.5 Key Exchange Status Types
737 This section defines all key exchange protocol status types that may be
738 returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets to
739 indicate the status of the protocol. Implementations may map the
740 status types to human readable error message. All types except the
741 SILC_SKE_STATUS_OK type must be sent in SILC_PACKET_FAILURE packet.
742 The length of status is 32 bits (4 bytes). Following status types are
748 Protocol were executed successfully.
751 1 SILC_SKE_STATUS_ERROR
753 Unknown error occured. No specific error type is defined.
756 2 SILC_SKE_STATUS_BAD_PAYLOAD
758 Provided KE payload were malformed or included bad fields.
761 3 SILC_SKE_STATUS_UNSUPPORTED_GROUP
763 None of the provided groups were supported.
766 4 SILC_SKE_STATUS_UNSUPPORTED_CIPHER
768 None of the provided ciphers were supported.
771 5 SILC_SKE_STATUS_UNSUPPORTED_PKCS
773 None of the provided public key algorithms were supported.
776 6 SILC_SKE_STATUS_UNSUPPORTED_HASH_FUNCTION
778 None of the provided hash functions were supported.
781 7 SILC_SKE_STATUS_UNSUPPORTED_HMAC
783 None of the provided HMACs were supported.
786 8 SILC_SKE_STATUS_UNSUPPORTED_PUBLIC_KEY
788 Provided public key type is not supported.
791 9 SILC_SKE_STATUS_INCORRECT_SIGNATURE
793 Provided signature was incorrect.
796 10 SILC_SKE_STATUS_BAD_VERSION
798 Provided version string was not acceptable.
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 may
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 3: 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 The length of status is 32 bits (4 bytes). Following status types are
977 Protocol was executed successfully.
982 Authentication failed.
986 4 Security Considerations
988 Security is central to the design of this protocol, and these security
989 considerations permeate the specification. Common security considerations
990 such as keeping private keys truly private and using adequate lengths for
991 symmetric and asymmetric keys must be followed in order to maintain the
992 security of this protocol.
998 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
999 Protocol Specification", Internet Draft, June 2000.
1001 [SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
1004 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
1007 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
1010 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
1013 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
1016 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
1019 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
1022 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
1025 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
1028 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
1029 Infrastructure, Certificate and CRL Profile", RFC 2459,
1032 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
1033 John Wiley & Sons, New York, NY, 1996.
1035 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
1038 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
1039 RFC 2412, November 1998.
1041 [ISAKMP] Maughan D., et al, "Internet Security Association and
1042 Key Management Protocol (ISAKMP)", RFC 2408, November
1045 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
1046 (IKE)", RFC 2409, November 1998.
1048 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
1049 Authentication", RFC 2104, February 1997.
1051 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
1052 Specifications, Version 2.0", RFC 2437, October 1998.
1064 EMail: priikone@poseidon.pspt.fi
1066 This Internet-Draft expires 6 Jun 2001