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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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
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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 When performing re-key with PFS selected this is the only payload that
406 is sent in the SKE protocol. The Key Exchange Start Payload is not sent
407 at all. However, this payload does not have all the fields present.
408 In re-key with PFS the public key and a possible signature data should
409 not be present. If they are present they must be ignored. The only
410 field that is present is the public data that is used to create the
411 new key material. In the re-key the Mutual Authentication flag must
414 This payload is sent inside SILC_PACKET_KEY_EXCHANGE_1 and inside
415 SILC_PACKET_KEY_EXCHANGE_2 packet types. The initiator uses the
416 SILC_PACKET_KEY_EXCHANGE_1 and the responder the latter.
418 The following diagram represent the Key Exchange 1 Payload.
424 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
425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
426 | Public Key Length | Public Key Type |
427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
429 ~ Public Key of the party (or certificate) ~
431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
432 | Public Data Length | |
433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
438 | Signature Length | |
439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
447 Figure 2: Key Exchange Payload
451 o Public Key Length (2 bytes) - The length of the Public Key
452 (or certificate) field, not including any other field.
454 o Public Key Type (2 bytes) - The public key (or certificate)
455 type. This field indicates the type of the public key in
456 the packet. Following types are defined:
458 1 SILC style public key (mandatory)
459 2 SSH2 style public key (optional)
460 3 X.509 Version 3 certificate (optional)
461 4 OpenPGP certificate (optional)
462 5 SPKI certificate (optional)
464 The only required type to support is type number 1. See
465 [SILC1] for the SILC public key specification. See
466 SSH public key specification in [SSH-TRANS]. See X.509v3
467 certificate specification in [PKIX-Part1]. See OpenPGP
468 certificate specification in [PGP]. See SPKI certificate
469 specification in [SPKI]. If this field includes zero (0)
470 or unsupported type number the protocol must be aborted
471 sending SILC_PACKET_FAILURE message and the connection should
472 be closed immediately.
474 o Public Data Length (2 bytes) - The length of the Public Data
475 field, not including any other field.
477 o Public Data (variable length) - The public data to be
478 sent to the receiver. See section 2.2 Key Exchange
479 Procedure for detailed description how this field is
480 computed. This value is binary encoded.
482 o Signature Length (2 bytes) - The length of the signature,
483 not including any other field.
485 o Signature Data (variable length) - The signature signed
486 by the sender. The receiver of this signature must
487 verify it. The verification is done using the public
488 key received in this same payload. See section 2.2
489 Key Exchange Procedure for detailed description how
490 to produce the signature. If the Mutual Authentication
491 flag is not set then initiator must not provide this
492 field and the Signature Length field must be set to zero (0)
493 value. If the flag is set then also the initiator must
494 provide this field. The responder always provides this
500 2.2 Key Exchange Procedure
502 The key exchange begins by sending SILC_PACKET_KEY_EXCHANGE packet with
503 Key Exchange Start Payload to select the security properties to be used
504 in the key exchange and later in the communication.
506 After Key Exchange Start Payload has been processed by both of the
507 parties the protocol proceeds as follows:
510 Setup: p is a large and public safe prime. This is one of the
511 Diffie Hellman groups. q is order of subgroup (largest
512 prime factor of p). g is a generator and is defined
513 along with the Diffie Hellman group.
515 1. Initiator generates a random number x, where 1 < x < q,
516 and computes e = g ^ x mod p. The result e is then
517 encoded into Key Exchange Payload and sent to the
520 If the Mutual Authentication flag is set then initiator
521 must also produce signature data SIGN_i which the responder
522 will verify. The initiator must compute a hash value
523 HASH_i = hash(Key Exchange Start Payload | public key
524 (or certificate) | e). It then signs the HASH_i value with
525 its private key resulting a signature SIGN_i.
527 2. Responder generates a random number y, where 1 < y < q,
528 and computes f = g ^ y mod p. It then computes the
529 shared secret KEY = e ^ y mod p, and, a hash value
530 HASH = hash(Key Exchange Start Payload data | public
531 key (or certificate) | e | f | KEY). It then signs
532 the HASH value with its private key resulting a signature
535 It then encodes its public key (or certificate), f and
536 SIGN into Key Exchange Payload and sends it to the
539 If the Mutual Authentication flag is set then the responder
540 should verify that the public key provided in the payload
541 is authentic, or if certificates are used it verifies the
542 certificate. The responder may accept the public key without
543 verifying it, however, doing so may result to insecure key
544 exchange (accepting the public key without verifying may be
545 desirable for practical reasons on many environments. For
546 long term use this is never desirable, in which case
547 certificates would be the preferred method to use). It then
548 computes the HASH_i value the same way initiator did in the
549 phase 1. It then verifies the signature SIGN_i from the
550 payload with the hash value HASH_i using the received public
553 3. Initiator verifies that the public key provided in
554 the payload is authentic, or if certificates are used
555 it verifies the certificate. The initiator may accept
556 the public key without verifying it, however, doing
557 so may result to insecure key exchange (accepting the
558 public key without verifying may be desirable for
559 practical reasons on many environments. For long term
560 use this is never desirable, in which case certificates
561 would be the preferred method to use).
563 Initiator then computes the shared secret KEY =
564 f ^ x mod p, and, a hash value HASH in the same way as
565 responder did in phase 2. It then verifies the
566 signature SIGN from the payload with the hash value
567 HASH using the received public key.
570 If any of these phases is to fail SILC_PACKET_FAILURE is sent to
571 indicate that the key exchange protocol has failed, and the connection
572 should be closed immediately. Any other packets must not be sent or
573 accepted during the key exchange except the SILC_PACKET_KEY_EXCHANGE_*,
574 SILC_PACKET_FAILURE and SILC_PACKET_SUCCESS packets.
576 The result of this protocol is a shared secret key material KEY and
577 a hash value HASH. The key material itself is not fit to be used as
578 a key, it needs to be processed further to derive the actual keys to be
579 used. The key material is also used to produce other security parameters
580 later used in the communication. See section 2.3 Processing the Key
581 Material for detailed description how to process the key material.
583 If the Mutual Authentication flag was set the protocol produces also
584 a hash value HASH_i. This value, however, must be discarded.
586 After the keys are processed the protocol is ended by sending the
587 SILC_PACKET_SUCCESS packet. Both entities send this packet to
588 each other. After this both parties will start using the new keys.
594 2.3 Processing the Key Material
596 Key Exchange protocol produces secret shared key material KEY. This
597 key material is used to derive the actual keys used in the encryption
598 of the communication channel. The key material is also used to derive
599 other security parameters used in the communication. Key Exchange
600 protocol produces a hash value HASH as well.
602 Keys are derived from the key material as follows:
605 Sending Initial Vector (IV) = hash(0 | KEY | HASH)
606 Receiving Initial Vector (IV) = hash(1 | KEY | HASH)
607 Sending Encryption Key = hash(2 | KEY | HASH)
608 Receiving Encryption Key = hash(3 | KEY | HASH)
609 HMAC Key = hash(4 | KEY | HASH)
613 The Initial Vector (IV) is used in the encryption when doing for
614 example CBC mode. As many bytes as needed are taken from the start of
615 the hash output for IV. Sending IV is for sending key and receiving IV
616 is for receiving key. For receiving party, the receiving IV is actually
617 sender's sending IV, and, the sending IV is actually sender's receiving
618 IV. Initiator uses IV's as they are (sending IV for sending and
619 receiving IV for receiving).
621 The Encryption Keys are derived as well from the hash(). If the hash()
622 output is too short for the encryption algorithm more key material is
623 produced in following manner:
626 K1 = hash(2 | KEY | HASH)
628 K3 = hash(KEY | K1 | K2) ...
630 Sending Encryption Key = K1 | K2 | K3 ...
633 K1 = hash(3 | KEY | HASH)
635 K3 = hash(KEY | K1 | K2) ...
637 Receiving Encryption Key = K1 | K2 | K3 ...
641 The key is distributed by hashing the previous hash with the original
642 key material. The final key is a concatenation of the hash values.
643 For Receiving Encryption Key the procedure is equivalent. Sending key
644 is used only for encrypting data to be sent. The receiving key is used
645 only to decrypt received data. For receiving party, the receive key is
646 actually sender's sending key, and, the sending key is actually sender's
647 receiving key. Initiator uses generated keys as they are (sending key
648 for sending and receiving key for sending).
650 The HMAC key is used to create MAC values to packets in the communication
651 channel. As many bytes as needed are taken from the start of the hash
654 These procedures are performed by all parties of the key exchange
655 protocol. This must be done before the protocol has been ended by
656 sending the SILC_PACKET_SUCCESS packet.
660 2.4 SILC Key Exchange Groups
662 Following groups may be used in the SILC Key Exchange protocol. The
663 first group diffie-hellman-group1 is mandatory, other groups maybe
664 negotiated to be used in the connection with Key Exchange Start Payload
665 and SILC_PACKET_KEY_EXCHANGE packet. However, the first group must be
666 proposed in the Key Exchange Start Payload regardless of any other
667 requested group (however, it does not have to be the first in the list).
671 2.4.1 diffie-hellman-group1
673 The length of this group is 1024 bits. This is mandatory group.
674 The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
679 179769313486231590770839156793787453197860296048756011706444
680 423684197180216158519368947833795864925541502180565485980503
681 646440548199239100050792877003355816639229553136239076508735
682 759914822574862575007425302077447712589550957937778424442426
683 617334727629299387668709205606050270810842907692932019128194
687 Its hexadecimal value is
690 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
691 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
692 EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
693 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
694 EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
699 The generator used with this prime is g = 2. The group order q is
702 This group was taken from the OAKLEY specification.
706 2.4.2 diffie-hellman-group2
708 The length of this group is 1536 bits. This is optional group.
709 The prime is 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }.
714 241031242692103258855207602219756607485695054850245994265411
715 694195810883168261222889009385826134161467322714147790401219
716 650364895705058263194273070680500922306273474534107340669624
717 601458936165977404102716924945320037872943417032584377865919
718 814376319377685986952408894019557734611984354530154704374720
719 774996976375008430892633929555996888245787241299381012913029
720 459299994792636526405928464720973038494721168143446471443848
721 8520940127459844288859336526896320919633919
724 Its hexadecimal value is
727 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
728 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
729 EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
730 E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
731 EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
732 C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
733 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
734 670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF
737 The generator used with this prime is g = 2. The group order q is
740 This group was taken from the OAKLEY specification.
744 2.5 Key Exchange Status Types
746 This section defines all key exchange protocol status types that may be
747 returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets to
748 indicate the status of the protocol. Implementations may map the
749 status types to human readable error message. All types except the
750 SILC_SKE_STATUS_OK type must be sent in SILC_PACKET_FAILURE packet.
751 The length of status is 32 bits (4 bytes). Following status types are
757 Protocol were executed successfully.
760 1 SILC_SKE_STATUS_ERROR
762 Unknown error occured. No specific error type is defined.
765 2 SILC_SKE_STATUS_BAD_PAYLOAD
767 Provided KE payload were malformed or included bad fields.
770 3 SILC_SKE_STATUS_UNSUPPORTED_GROUP
772 None of the provided groups were supported.
775 4 SILC_SKE_STATUS_UNSUPPORTED_CIPHER
777 None of the provided ciphers were supported.
780 5 SILC_SKE_STATUS_UNSUPPORTED_PKCS
782 None of the provided public key algorithms were supported.
785 6 SILC_SKE_STATUS_UNSUPPORTED_HASH_FUNCTION
787 None of the provided hash functions were supported.
790 7 SILC_SKE_STATUS_UNSUPPORTED_HMAC
792 None of the provided HMACs were supported.
795 8 SILC_SKE_STATUS_UNSUPPORTED_PUBLIC_KEY
797 Provided public key type is not supported.
800 9 SILC_SKE_STATUS_INCORRECT_SIGNATURE
802 Provided signature was incorrect.
805 10 SILC_SKE_STATUS_BAD_VERSION
807 Provided version string was not acceptable.
815 3 SILC Connection Authentication Protocol
817 Purpose of Connection Authentication protocol is to authenticate the
818 connecting party with server. Usually connecting party is client but
819 server may connect to server as well. Its other purpose is to provide
820 information for the server about which type of connection this is.
821 The type defines whether this is client, server or router connection.
822 Server uses this information to create the ID for the connection. After
823 the authentication protocol has been successfully completed
824 SILC_PACKET_NEW_ID must be sent to the connecting party by the server.
825 See section New ID Payload in [SILC2] for detailed description for this
828 Server must verify the authentication data received and if it is to fail
829 the authentication must be failed by sending SILC_PACKET_FAILURE packet.
830 If everything checks out fine the protocol is ended by server by sending
831 SILC_PACKET_SUCCESS packet.
833 The protocol is executed after the SILC Key Exchange protocol. It must
834 not be executed in any other time. As it is performed after key exchange
835 protocol all traffic in the connection authentication protocol is
836 encrypted with the exchanged keys.
838 The protocol is started by the connecting party by sending
839 SILC_PACKET_CONNECTION_AUTH packet with Connection Auth Payload,
840 described in the next section. This payload must include the
841 authentication data. Authentication data is set according
842 authentication method that must be known by both parties. If connecting
843 party does not know what is the mandatory authentication method it may
844 request it from the server by sending SILC_PACKET_CONNECTION_AUTH_REQUEST
845 packet. This packet is not part of this protocol and is described in
846 section Connection Auth Request Payload in [SILC2]. However, if
847 connecting party already knows the mandatory authentication method
848 sending the request is not necessary.
850 See [SILC1] and section Connection Auth Request Payload in [SILC2] also
851 for the list of different authentication methods. Authentication method
852 may also be NONE, in which case the server does not require
853 authentication at all. However, in this case the protocol still must be
854 executed; the authentication data just is empty indicating no
855 authentication is required.
857 If authentication method is passphrase the authentication data is
858 plaintext passphrase. As the payload is entirely encrypted it is safe
859 to have plaintext passphrase. 3.2.1 Passphrase Authentication for
863 If authentication method is public key authentication the authentication
864 data is signature of the hash value HASH plus Key Exchange Start Payload,
865 established by the SILC Key Exchange protocol. This signature must then
866 be verified by the server. See section 3.2.2 Public Key Authentication
867 for more information.
869 The connecting party of this protocol must wait after successful execution
870 of this protocol for the SILC_PACKET_NEW_ID packet where it will receive
871 the ID it will be using in the SILC network. Connecting party cannot
872 start normal SILC session (sending messages or commands) until it has
873 received its ID. The ID's are always created by the server except
874 for server to server connection where servers create their own ID's.
879 3.1 Connection Auth Payload
881 Client sends this payload to authenticate itself to the server. Server
882 connecting to another server also sends this payload. Server receiving
883 this payload must verify all the data in it and if something is to fail
884 the authentication must be failed by sending SILC_PACKET_FAILURE packet.
886 The payload may only be sent with SILC_PACKET_CONNECTION_AUTH packet.
887 It must not be sent in any other packet type. Following diagram
888 represent the Connection Auth Payload.
894 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
895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
896 | Payload Length | Connection Type |
897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
899 ~ Authentication Data ~
901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
905 Figure 3: Connection Auth Payload
909 o Payload Length (2 bytes) - Length of the entire Connection
912 o Connection Type (2 bytes) - Indicates the type of the
913 connection. See section Connection Auth Request Payload
914 in [SILC2] for the list of connection types. This field must
915 include valid connection type or the packet must be discarded
916 and authentication must be failed.
918 o Authentication Data (variable length) - The actual
919 authentication data. Contents of this depends on the
920 authentication method known by both parties. If no
921 authentication is required this field does not exist.
926 3.2 Connection Authentication Types
928 SILC supports two authentication types to be used in the connection
929 authentication protocol; passphrase or public key based authentication.
930 Following sections defines the authentication methods. See [SILC2]
931 for defined numerical authentication method types.
935 3.2.1 Passphrase Authentication
937 Passphrase authentication or pre-shared-key base authentication is
938 simply an authentication where the party that wants to authenticate
939 itself to the other end sends the passphrase that is required by
940 the other end, for example server.
942 If the passphrase matches with the one in the server's end the
943 authentication is successful. Otherwise SILC_PACKET_FAILURE must be
944 sent to the sender and the protocol execution fails.
946 This is required authentication method to be supported by all SILC
951 3.2.2 Public Key Authentication
953 Public key authentication may be used if passphrase based authentication
954 is not desired. The public key authentication works by sending a
955 signature as authentication data to the other end, say, server. The
956 server must then verify the signature by the public key of the sender,
957 which the server has received earlier in SKE protocol.
959 The signature is computed using the private key of the sender by signing
960 the HASH value provided by the SKE protocol previously, and the Key
961 Exchange Start Payload from SKE protocol that was sent to the server.
962 The server must verify the data, thus it must keep the HASH and the
963 Key Exchange Start Payload saved during SKE and authentication protocols.
965 If the verified signature matches the sent signature, the authentication
966 were successful and SILC_PACKET_SUCCESS is sent. If it failed the protocol
967 execution is stopped and SILC_PACKET_FAILURE is sent.
969 This is required authentication method to be supported by all SILC
974 3.3 Connection Authentication Status Types
976 This section defines all connection authentication status types that
977 may be returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets
978 to indicate the status of the protocol. Implementations may map the
979 status types to human readable error message. All types except the
980 SILC_AUTH_STATUS_OK type must be sent in SILC_PACKET_FAILURE packet.
981 The length of status is 32 bits (4 bytes). Following status types are
986 Protocol was executed successfully.
991 Authentication failed.
995 4 Security Considerations
997 Security is central to the design of this protocol, and these security
998 considerations permeate the specification. Common security considerations
999 such as keeping private keys truly private and using adequate lengths for
1000 symmetric and asymmetric keys must be followed in order to maintain the
1001 security of this protocol.
1007 [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
1008 Protocol Specification", Internet Draft, June 2000.
1010 [SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
1013 [IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
1016 [IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
1019 [IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
1022 [IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
1025 [IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
1028 [SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
1031 [PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
1034 [SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
1037 [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
1038 Infrastructure, Certificate and CRL Profile", RFC 2459,
1041 [Schneier] Schneier, B., "Applied Cryptography Second Edition",
1042 John Wiley & Sons, New York, NY, 1996.
1044 [Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
1047 [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
1048 RFC 2412, November 1998.
1050 [ISAKMP] Maughan D., et al, "Internet Security Association and
1051 Key Management Protocol (ISAKMP)", RFC 2408, November
1054 [IKE] Harkins D., and Carrel D., "The Internet Key Exchange
1055 (IKE)", RFC 2409, November 1998.
1057 [HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
1058 Authentication", RFC 2104, February 1997.
1060 [PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
1061 Specifications, Version 2.0", RFC 2437, October 1998.
1073 EMail: priikone@poseidon.pspt.fi
1075 This Internet-Draft expires 6 Jun 2001