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+.pl 10.0i
+.po 0
+.ll 7.2i
+.lt 7.2i
+.nr LL 7.2i
+.nr LT 7.2i
+.ds LF Riikonen
+.ds RF FORMFEED[Page %]
+.ds CF
+.ds LH Internet-Draft
+.ds RH XXX
+.ds CH
+.na
+.hy 0
+.in 0
+.nf
+Network Working Group P. Riikonen
+Internet-Draft
+draft-riikonen-silc-ke-auth-04.txt XXX
+Expires: XXX
+
+.in 3
+
+.ce 2
+SILC Key Exchange and Authentication Protocols
+<draft-riikonen-silc-ke-auth-04.txt>
+
+.ti 0
+Status of this Memo
+
+This document is an Internet-Draft and is in full conformance with
+all provisions of Section 10 of RFC 2026. Internet-Drafts are
+working documents of the Internet Engineering Task Force (IETF), its
+areas, and its working groups. Note that other groups may also
+distribute working documents as Internet-Drafts.
+
+Internet-Drafts are draft documents valid for a maximum of six months
+and may be updated, replaced, or obsoleted by other documents at any
+time. It is inappropriate to use Internet-Drafts as reference
+material or to cite them other than as "work in progress."
+
+The list of current Internet-Drafts can be accessed at
+http://www.ietf.org/ietf/1id-abstracts.txt
+
+The list of Internet-Draft Shadow Directories can be accessed at
+http://www.ietf.org/shadow.html
+
+The distribution of this memo is unlimited.
+
+
+.ti 0
+Abstract
+
+This memo describes two protocols used in the Secure Internet Live
+Conferencing (SILC) protocol, specified in the Secure Internet Live
+Conferencing, Protocol Specification internet-draft [SILC1]. The
+SILC Key Exchange (SKE) protocol provides secure key exchange between
+two parties resulting into shared secret key material. The protocol
+is based on Diffie-Hellman key exchange algorithm and its functionality
+is derived from several key exchange protocols. SKE uses best parts
+of the SSH2 Key Exchange protocol, Station-To-Station (STS) protocol
+and the OAKLEY Key Determination protocol [OAKLEY].
+
+The SILC Connection Authentication protocol provides user level
+authentication used when creating connections in SILC network. The
+protocol is transparent to the authentication data which means that it
+can be used to authenticate the user with, for example, passphrase
+(pre-shared-secret) or public key (and certificate).
+
+
+
+.ti 0
+Table of Contents
+
+.nf
+1 Introduction .................................................. 2
+ 1.1 Requirements Terminology .................................. 3
+2 SILC Key Exchange Protocol .................................... 3
+ 2.1 Key Exchange Payloads ..................................... 4
+ 2.1.1 Key Exchange Start Payload .......................... 4
+ 2.1.2 Key Exchange Payload ................................ 8
+ 2.2 Key Exchange Procedure .................................... 10
+ 2.3 Processing the Key Material ............................... 12
+ 2.4 SILC Key Exchange Groups .................................. 13
+ 2.4.1 diffie-hellman-group1 ............................... 14
+ 2.4.2 diffie-hellman-group2 ............................... 14
+ 2.5 Key Exchange Status Types ................................. 15
+3 SILC Connection Authentication Protocol ....................... 16
+ 3.1 Connection Auth Payload ................................... 18
+ 3.2 Connection Authentication Types ........................... 18
+ 3.2.1 Passphrase Authentication ........................... 19
+ 3.2.2 Public Key Authentication ........................... 19
+ 3.3 Connection Authentication Status Types .................... 19
+4 Security Considerations ....................................... 20
+5 References .................................................... 20
+6 Author's Address .............................................. 21
+
+
+.ti 0
+List of Figures
+
+.nf
+Figure 1: Key Exchange Start Payload
+Figure 2: Key Exchange Payload
+Figure 3: Connection Auth Payload
+
+
+.ti 0
+1 Introduction
+
+This memo describes two protocols used in the Secure Internet Live
+Conferencing (SILC) protocol specified in the Secure Internet Live
+Conferencing, Protocol Specification Internet-Draft [SILC1]. The
+SILC Key Exchange (SKE) protocol provides secure key exchange between
+two parties resulting into shared secret key material. The protocol
+is based on Diffie-Hellman key exchange algorithm and its functionality
+is derived from several key exchange protocols. SKE uses best parts
+of the SSH2 Key Exchange protocol, Station-To-Station (STS) protocol
+and the OAKLEY Key Determination protocol.
+
+The SILC Connection Authentication protocol provides user level
+authentication used when creating connections in SILC network. The
+protocol is transparent to the authentication data which means that it
+can be used to authenticate the user with, for example, pass phrase
+(pre-shared- secret) or public key (and certificate).
+
+The basis of secure SILC session requires strong and secure key exchange
+protocol and authentication. The authentication protocol is entirely
+secured and no authentication data is ever sent in the network without
+encrypting and authenticating it first. Thus, authentication protocol
+may be used only after the key exchange protocol has been successfully
+completed.
+
+This document refers constantly to other SILC protocol specification
+Internet Drafts that are a must read for those who wants to understand
+the function of these protocols. The most important references are
+the Secure Internet Live Conferencing, Protocol Specification [SILC1]
+and the SILC Packet Protocol [SILC2] Internet Drafts.
+
+The protocol is intended to be used with the SILC protocol thus it
+does not define own framework that could be used. The framework is
+provided by the SILC protocol.
+
+
+.ti 0
+1.1 Requirements Terminology
+
+The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED,
+MAY, and OPTIONAL, when they appear in this document, are to be
+interpreted as described in [RFC2119].
+
+
+.ti 0
+2 SILC Key Exchange Protocol
+
+SILC Key Exchange Protocol (SKE) is used to exchange shared secret
+between connecting entities. The result of this protocol is a key
+material used to secure the communication channel. The protocol uses
+Diffie-Hellman key exchange algorithm and its functionality is derived
+from several key exchange protocols. SKE uses best parts of the SSH2
+Key Exchange protocol, Station-To-Station (STS) protocol and the OAKLEY
+Key Determination protocol. The protocol does not claim any conformance
+to any of these protocols, they were merely used as a reference when
+designing this protocol.
+
+The purpose of SILC Key Exchange protocol is to create session keys to
+be used in current SILC session. The keys are valid only for some period
+of time (usually an hour) or at most until the session ends. These keys
+are used to protect packets like commands, command replies and other
+communication between two entities. If connection is server to router
+connection, the keys are used to protect all traffic between those
+servers. In client connections usually all the packets are protected
+with this key except channel messages; channels has their own keys and
+they are not exchanged with this protocol.
+
+The Diffie-Hellman implementation used in the SILC SHOULD be compliant
+to the PKCS #3.
+
+
+.ti 0
+2.1 Key Exchange Payloads
+
+During the key exchange procedure public data is sent between initiator
+and responder. This data is later used in the key exchange procedure.
+There are several payloads used in the key exchange. As for all SILC
+packets, SILC Packet Header, described in [SILC2], is at the start of
+all packets. The same is done with these payloads as well. All the
+fields in the payloads are always in MSB (most significant byte first)
+order. Following descriptions of these payloads.
+
+
+.ti 0
+2.1.1 Key Exchange Start Payload
+
+The key exchange between two entities MUST be started by sending the
+SILC_PACKET_KEY_EXCHANGE packet containing Key Exchange Start Payload.
+Initiator sends the Key Exchange Start Payload to the responder filled
+with all security properties it supports. The responder then checks
+whether it supports the security properties.
+
+It then sends a Key Exchange Start Payload to the initiator filled with
+security properties it selected from the original payload. The payload
+sent by responder MUST include only one chosen property per list.
+
+The Key Exchange Start Payload is used to tell connecting entities what
+security properties and algorithms should be used in the communication.
+The Key Exchange Start Payload is sent only once per session. Even if
+the PFS (Perfect Forward Secrecy) flag is set the Key Exchange Start
+Payload is not re-sent. When PFS is desired the Key Exchange Payloads
+are sent to negotiate new key material. The procedure is equivalent to
+the very first negotiation except that the Key Exchange Start Payload
+is not sent.
+
+As this payload is used only with the very first key exchange the payload
+is never encrypted, as there are no keys to encrypt it with.
+
+A cookie is also sent in this payload. A cookie is used to randomize the
+payload so that none of the key exchange parties can determine this
+payload before the key exchange procedure starts. The cookie MUST be
+returned to the original sender by the responder.
+
+Following diagram represents the Key Exchange Start Payload. The lists
+mentioned below are always comma (`,') separated and the list MUST
+not include spaces (` ').
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| RESERVED | Flags | Payload Length |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
++ +
+| |
++ Cookie +
+| |
++ +
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Version String Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Version String ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Key Exchange Grp Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Key Exchange Groups ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| PKCS Alg Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ PKCS Algorithms ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Encryption Alg Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Encryption Algorithms ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Hash Alg Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Hash Algorithms ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| HMAC Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ HMACs ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Compression Alg Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Compression Algorithms ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 1: Key Exchange Start Payload
+
+
+
+.in 6
+o RESERVED (1 byte) - Reserved field. Sender fills this with
+ zero (0) value.
+
+o Flags (1 byte) - Indicates flags to be used in the key
+ exchange. Several flags can be set at once by ORing the
+ flags together. The following flags are reserved for this
+ field:
+
+ No flags 0x00
+
+ In this case the field is ignored.
+
+ No Reply 0x01
+
+ If set the receiver of the payload does not reply to
+ the packet.
+
+ PFS 0x02
+
+ Perfect Forward Secrecy (PFS) to be used in the
+ key exchange protocol. If not set, re-keying
+ is performed using the old key. See the [SILC1]
+ for more information on this issue. When PFS is
+ used, re-keying and creating new keys for any
+ particular purpose MUST cause new key exchange.
+ In this key exchange only the Key Exchange Payload
+ is sent and the Key Exchange Start Payload MUST
+ NOT be sent. When doing PFS the Key Exchange
+ Payloads are encrypted with the old keys.
+
+ Mutual Authentication 0x04
+
+ Both of the parties will perform authentication
+ by providing signed data for the other party to
+ verify. By default, only responder will provide
+ the signature data. If this is set then the
+ initiator must also provide it. Initiator MAY
+ set this but also responder MAY set this even if
+ initiator did not set it.
+
+ Rest of the flags are reserved for the future and
+ MUST NOT be set.
+
+o Payload Length (2 bytes) - Length of the entire Key Exchange
+ Start payload, not including any other field.
+
+o Cookie (16 bytes) - Cookie that randomize this payload so
+ that each of the party cannot determine the payload before
+ hand.
+
+o Version String Length (2 bytes) - The length of the Version
+ String field, not including any other field.
+
+o Version String (variable length) - Indicates the version of
+ the sender of this payload. Initiator sets this when sending
+ the payload and responder sets this when it replies by sending
+ this payload. See [SILC1] for definition of the version
+ string format.
+
+o Key Exchange Grp Length (2 bytes) - The length of the
+ key exchange group list, not including any other field.
+
+o Key Exchange Group (variable length) - The list of
+ key exchange groups. See the section 2.4 SILC Key Exchange
+ Groups for definitions of these groups.
+
+o PKCS Alg Length (2 bytes) - The length of the PKCS algorithms
+ list, not including any other field.
+
+o PKCS Algorithms (variable length) - The list of PKCS
+ algorithms.
+
+o Encryption Alg Length (2 bytes) - The length of the encryption
+ algorithms list, not including any other field.
+
+o Encryption Algorithms (variable length) - The list of
+ encryption algorithms.
+
+o Hash Alg Length (2 bytes) - The length of the Hash algorithm
+ list, not including any other field.
+
+o Hash Algorithms (variable length) - The list of Hash
+ algorithms. The hash algorithms are mainly used in the
+ SKE protocol.
+
+o HMAC Length (2 bytes) - The length of the HMAC list, not
+ including any other field.
+
+o HMACs (variable length) - The list of HMACs. The HMAC's
+ are used to compute the Message Authentication Codes (MAC)
+ of the SILC packets.
+
+o Compression Alg Length (2 bytes) - The length of the
+ compression algorithms list, not including any other field.
+
+o Compression Algorithms (variable length) - The list of
+ compression algorithms.
+.in 3
+
+
+.ti 0
+2.1.2 Key Exchange Payload
+
+Key Exchange payload is used to deliver the public key (or certificate),
+the computed Diffie-Hellman public value and possibly signature data
+from one party to the other. When initiator is using this payload
+and the Mutual Authentication flag is not set then the initiator MUST
+NOT provide the signature data. If the flag is set then the initiator
+MUST provide the signature data so that the responder can verify it.
+
+The Mutual Authentication flag is usually used only if a separate
+authentication protocol will not be executed for the initiator of the
+protocol. This is case for example when the SKE is performed between
+two SILC clients. In normal case, where client is connecting to the
+server, or server is connecting to the router the Mutual Authentication
+flag is not necessary.
+
+When performing re-key with PFS selected this is the only payload that
+is sent in the SKE protocol. The Key Exchange Start Payload MUST NOT
+be sent at all. However, this payload does not have all the fields
+present. In the re-key with PFS the public key and a possible signature
+data SHOULD NOT be present. If they are present they MUST be ignored.
+The only field that is present is the Public Data that is used to create
+the new key material. In the re-key the Mutual Authentication flag, that
+may be set in the initial negotiation, MUST also be ignored.
+
+This payload is sent inside SILC_PACKET_KEY_EXCHANGE_1 and inside
+SILC_PACKET_KEY_EXCHANGE_2 packet types. The initiator uses the
+SILC_PACKET_KEY_EXCHANGE_1 and the responder the latter.
+
+The following diagram represent the Key Exchange Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Public Key Length | Public Key Type |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Public Key of the party (or certificate) ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Public Data Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Public Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Signature Length | |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
+| |
+~ Signature Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 2: Key Exchange Payload
+
+
+.in 6
+o Public Key Length (2 bytes) - The length of the Public Key
+ (or certificate) field, not including any other field.
+
+o Public Key Type (2 bytes) - The public key (or certificate)
+ type. This field indicates the type of the public key in
+ the packet. Following types are defined:
+
+ 1 SILC style public key (mandatory)
+ 2 SSH2 style public key (optional)
+ 3 X.509 Version 3 certificate (optional)
+ 4 OpenPGP certificate (optional)
+ 5 SPKI certificate (optional)
+
+ The only required type to support is type number 1. See
+ [SILC1] for the SILC public key specification. See
+ SSH public key specification in [SSH-TRANS]. See X.509v3
+ certificate specification in [PKIX-Part1]. See OpenPGP
+ certificate specification in [PGP]. See SPKI certificate
+ specification in [SPKI]. If this field includes zero (0)
+ or unsupported type number the protocol MUST be aborted
+ sending SILC_PACKET_FAILURE message and the connection SHOULD
+ be closed immediately.
+
+o Public Key (or certificate) (variable length) - The
+ public key or certificate.
+
+o Public Data Length (2 bytes) - The length of the Public Data
+ field, not including any other field.
+
+o Public Data (variable length) - The public data to be
+ sent to the receiver. See section 2.2 Key Exchange
+ Procedure for detailed description how this field is
+ computed. This value is binary encoded.
+
+o Signature Length (2 bytes) - The length of the signature,
+ not including any other field.
+
+o Signature Data (variable length) - The signature signed
+ by the sender. The receiver of this signature MUST
+ verify it. The verification is done using the sender's
+ public key. See section 2.2 Key Exchange Procedure for
+ detailed description how to produce the signature. If
+ the Mutual Authentication flag is not set then initiator
+ MUST NOT provide this field and the Signature Length field
+ MUST be set to zero (0) value. If the flag is set then
+ also the initiator MUST provide this field. The responder
+ MUST always provide this field.
+.in 3
+
+
+.ti 0
+2.2 Key Exchange Procedure
+
+The key exchange begins by sending SILC_PACKET_KEY_EXCHANGE packet with
+Key Exchange Start Payload to select the security properties to be used
+in the key exchange and later in the communication.
+
+After Key Exchange Start Payload has been processed by both of the
+parties the protocol proceeds as follows:
+
+
+Setup: p is a large and public safe prime. This is one of the
+ Diffie Hellman groups. q is order of subgroup (largest
+ prime factor of p). g is a generator and is defined
+ along with the Diffie Hellman group.
+
+ 1. Initiator generates a random number x, where 1 < x < q,
+ and computes e = g ^ x mod p. The result e is then
+ encoded into Key Exchange Payload and sent to the
+ responder.
+
+ If the Mutual Authentication flag is set then initiator
+ MUST also produce signature data SIGN_i which the responder
+ will verify. The initiator MUST compute a hash value
+ HASH_i = hash(Key Exchange Start Payload | public key
+ (or certificate) | e). It then signs the HASH_i value with
+ its private key resulting a signature SIGN_i.
+
+ 2. Responder generates a random number y, where 1 < y < q,
+ and computes f = g ^ y mod p. It then computes the
+ shared secret KEY = e ^ y mod p, and, a hash value
+ HASH = hash(Key Exchange Start Payload data | public
+ key (or certificate) | e | f | KEY). It then signs
+ the HASH value with its private key resulting a signature
+ SIGN.
+
+ It then encodes its public key (or certificate), f and
+ SIGN into Key Exchange Payload and sends it to the
+ initiator.
+
+ If the Mutual Authentication flag is set then the responder
+ SHOULD verify that the public key provided in the payload
+ is authentic, or if certificates are used it verifies the
+ certificate. The responder MAY accept the public key without
+ verifying it, however, doing so may result to insecure key
+ exchange (accepting the public key without verifying may be
+ desirable for practical reasons on many environments. For
+ long term use this is never desirable, in which case
+ certificates would be the preferred method to use). It then
+ computes the HASH_i value the same way initiator did in the
+ phase 1. It then verifies the signature SIGN_i from the
+ payload with the hash value HASH_i using the received public
+ key.
+
+ 3. Initiator verifies that the public key provided in
+ the payload is authentic, or if certificates are used
+ it verifies the certificate. The initiator MAY accept
+ the public key without verifying it, however, doing
+ so may result to insecure key exchange (accepting the
+ public key without verifying may be desirable for
+ practical reasons on many environments. For long term
+ use this is never desirable, in which case certificates
+ would be the preferred method to use).
+
+ Initiator then computes the shared secret KEY =
+ f ^ x mod p, and, a hash value HASH in the same way as
+ responder did in phase 2. It then verifies the
+ signature SIGN from the payload with the hash value
+ HASH using the received public key.
+
+
+If any of these phases is to fail the SILC_PACKET_FAILURE MUST be sent
+to indicate that the key exchange protocol has failed, and the connection
+SHOULD be closed immediately. Any other packets MUST NOT be sent or
+accepted during the key exchange except the SILC_PACKET_KEY_EXCHANGE_*,
+SILC_PACKET_FAILURE and SILC_PACKET_SUCCESS packets.
+
+The result of this protocol is a shared secret key material KEY and
+a hash value HASH. The key material itself is not fit to be used as
+a key, it needs to be processed further to derive the actual keys to be
+used. The key material is also used to produce other security parameters
+later used in the communication. See section 2.3 Processing the Key
+Material for detailed description how to process the key material.
+
+If the Mutual Authentication flag was set the protocol produces also
+a hash value HASH_i. This value, however, must be discarded.
+
+After the keys are processed the protocol is ended by sending the
+SILC_PACKET_SUCCESS packet. Both entities send this packet to
+each other. After this both parties will start using the new keys.
+
+
+.ti 0
+2.3 Processing the Key Material
+
+Key Exchange protocol produces secret shared key material KEY. This
+key material is used to derive the actual keys used in the encryption
+of the communication channel. The key material is also used to derive
+other security parameters used in the communication. Key Exchange
+protocol produces a hash value HASH as well.
+
+The keys MUST be derived from the key material as follows:
+
+.in 6
+Sending Initial Vector (IV) = hash(0 | KEY | HASH)
+Receiving Initial Vector (IV) = hash(1 | KEY | HASH)
+Sending Encryption Key = hash(2 | KEY | HASH)
+Receiving Encryption Key = hash(3 | KEY | HASH)
+HMAC Key = hash(4 | KEY | HASH)
+.in 3
+
+
+The Initial Vector (IV) is used in the encryption when doing for
+example CBC mode. As many bytes as needed are taken from the start of
+the hash output for IV. Sending IV is for sending key and receiving IV
+is for receiving key. For receiving party, the receiving IV is actually
+sender's sending IV, and, the sending IV is actually sender's receiving
+IV. Initiator uses IV's as they are (sending IV for sending and
+receiving IV for receiving).
+
+The Encryption Keys are derived as well from the hash(). If the hash()
+output is too short for the encryption algorithm more key material MUST
+be produced in the following manner:
+
+.in 6
+K1 = hash(2 | KEY | HASH)
+K2 = hash(KEY | HASH | K1)
+K3 = hash(KEY | HASH | K1 | K2) ...
+
+Sending Encryption Key = K1 | K2 | K3 ...
+
+
+K1 = hash(3 | KEY | HASH)
+K2 = hash(KEY | HASH | K1)
+K3 = hash(KEY | HASH | K1 | K2) ...
+
+Receiving Encryption Key = K1 | K2 | K3 ...
+.in 3
+
+
+The key is distributed by hashing the previous hash with the original
+key material. The final key is a concatenation of the hash values.
+For Receiving Encryption Key the procedure is equivalent. Sending key
+is used only for encrypting data to be sent. The receiving key is used
+only to decrypt received data. For receiving party, the receive key is
+actually sender's sending key, and, the sending key is actually sender's
+receiving key. Initiator uses generated keys as they are (sending key
+for sending and receiving key for receiving).
+
+The HMAC key is used to create MAC values to packets in the communication
+channel. As many bytes as needed are taken from the start of the hash
+output.
+
+These procedures are performed by all parties of the key exchange
+protocol. This MUST be done before the protocol has been ended by
+sending the SILC_PACKET_SUCCESS packet.
+
+This same procedure is used in the SILC in some other circumstances
+as well. Any changes to this procedure is mentioned separately when
+this procedure is needed. See the [SILC1] and the [SILC2] for these
+circumstances.
+
+
+.ti 0
+2.4 SILC Key Exchange Groups
+
+The Following groups may be used in the SILC Key Exchange protocol.
+The first group diffie-hellman-group1 is REQUIRED, other groups MAY be
+negotiated to be used in the connection with Key Exchange Start Payload
+and SILC_PACKET_KEY_EXCHANGE packet. However, the first group MUST be
+proposed in the Key Exchange Start Payload regardless of any other
+requested group (however, it does not have to be the first in the list).
+
+
+.ti 0
+2.4.1 diffie-hellman-group1
+
+The length of this group is 1024 bits. This is REQUIRED group.
+The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
+
+Its decimal value is
+
+.in 6
+179769313486231590770839156793787453197860296048756011706444
+423684197180216158519368947833795864925541502180565485980503
+646440548199239100050792877003355816639229553136239076508735
+759914822574862575007425302077447712589550957937778424442426
+617334727629299387668709205606050270810842907692932019128194
+467627007
+.in 3
+
+Its hexadecimal value is
+
+.in 6
+FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
+29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
+EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
+E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
+EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
+FFFFFFFF FFFFFFFF
+.in 3
+
+
+The generator used with this prime is g = 2. The group order q is
+(p - 1) / 2.
+
+This group was taken from the OAKLEY specification.
+
+
+.ti 0
+2.4.2 diffie-hellman-group2
+
+The length of this group is 1536 bits. This is OPTIONAL group.
+The prime is 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }.
+
+Its decimal value is
+
+.in 6
+241031242692103258855207602219756607485695054850245994265411
+694195810883168261222889009385826134161467322714147790401219
+650364895705058263194273070680500922306273474534107340669624
+601458936165977404102716924945320037872943417032584377865919
+814376319377685986952408894019557734611984354530154704374720
+774996976375008430892633929555996888245787241299381012913029
+459299994792636526405928464720973038494721168143446471443848
+8520940127459844288859336526896320919633919
+.in 3
+
+Its hexadecimal value is
+
+.in 6
+FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
+29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
+EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
+E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
+EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
+C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
+83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
+670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF
+.in 3
+
+The generator used with this prime is g = 2. The group order q is
+(p - 1) / 2.
+
+This group was taken from the OAKLEY specification.
+
+
+.ti 0
+2.5 Key Exchange Status Types
+
+This section defines all key exchange protocol status types that may
+be returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets
+to indicate the status of the protocol. Implementations may map the
+status types to human readable error message. All types except the
+SILC_SKE_STATUS_OK type MUST be sent in SILC_PACKET_FAILURE packet.
+The length of status is 32 bits (4 bytes). The following status types
+are defined:
+
+.in 6
+0 SILC_SKE_STATUS_OK
+
+ Protocol were executed successfully.
+
+
+1 SILC_SKE_STATUS_ERROR
+
+ Unknown error occurred. No specific error type is defined.
+
+
+2 SILC_SKE_STATUS_BAD_PAYLOAD
+
+ Provided KE payload were malformed or included bad fields.
+
+
+3 SILC_SKE_STATUS_UNSUPPORTED_GROUP
+
+ None of the provided groups were supported.
+
+
+4 SILC_SKE_STATUS_UNSUPPORTED_CIPHER
+
+ None of the provided ciphers were supported.
+
+
+5 SILC_SKE_STATUS_UNSUPPORTED_PKCS
+
+ None of the provided public key algorithms were supported.
+
+
+6 SILC_SKE_STATUS_UNSUPPORTED_HASH_FUNCTION
+
+ None of the provided hash functions were supported.
+
+
+7 SILC_SKE_STATUS_UNSUPPORTED_HMAC
+
+ None of the provided HMACs were supported.
+
+
+8 SILC_SKE_STATUS_UNSUPPORTED_PUBLIC_KEY
+
+ Provided public key type is not supported.
+
+
+9 SILC_SKE_STATUS_INCORRECT_SIGNATURE
+
+ Provided signature was incorrect.
+
+
+10 SILC_SKE_STATUS_BAD_VERSION
+
+ Provided version string was not acceptable.
+
+11 SILC_SKE_STATUS_INVALID_COOKIE
+
+ The cookie in the Key Exchange Start Payload was malformed,
+ because responder modified the cookie.
+.in 3
+
+
+.ti 0
+3 SILC Connection Authentication Protocol
+
+Purpose of Connection Authentication protocol is to authenticate the
+connecting party with server. Usually connecting party is client but
+server may connect to router server as well. Its other purpose is to
+provide information for the server about which type of connection this
+is. The type defines whether this is client, server or router
+connection. Server uses this information to create the ID for the
+connection.
+
+After the authentication protocol has been successfully completed
+SILC_PACKET_NEW_ID must be sent to the connecting client by the server.
+See the [SILC1] for the details of the connecting procedure.
+
+Server MUST verify the authentication data received and if it is to fail
+the authentication MUST be failed by sending SILC_PACKET_FAILURE packet.
+If everything checks out fine the protocol is ended by server by sending
+SILC_PACKET_SUCCESS packet.
+
+The protocol is executed after the SILC Key Exchange protocol. It MUST
+NOT be executed in any other time. As it is performed after key exchange
+protocol all traffic in the connection authentication protocol is
+encrypted with the exchanged keys.
+
+The protocol MUST be started by the connecting party by sending the
+SILC_PACKET_CONNECTION_AUTH packet with Connection Auth Payload,
+described in the next section. This payload MUST include the
+authentication data. The authentication data is set according
+authentication method that MUST be known by both parties. If connecting
+party does not know what is the mandatory authentication method it MAY
+request it from the server by sending SILC_PACKET_CONNECTION_AUTH_REQUEST
+packet. This packet is not part of this protocol and is described in
+section Connection Auth Request Payload in [SILC2]. However, if
+connecting party already knows the mandatory authentication method
+sending the request is not necessary.
+
+See [SILC1] and section Connection Auth Request Payload in [SILC2] also
+for the list of different authentication methods. Authentication method
+MAY also be NONE, in which case the server does not require
+authentication at all. However, in this case the protocol still MUST be
+executed; the authentication data just is empty indicating no
+authentication is required.
+
+If authentication method is passphrase the authentication data is
+plaintext passphrase. As the payload is entirely encrypted it is safe
+to have plaintext passphrase. See the section 3.2.1 Passphrase
+Authentication for more information.
+
+If authentication method is public key authentication the authentication
+data is signature of the hash value HASH plus Key Exchange Start Payload,
+established by the SILC Key Exchange protocol. This signature MUST then
+be verified by the server. See the section 3.2.2 Public Key
+Authentication for more information.
+
+The connecting client of this protocol MUST wait after successful execution
+of this protocol for the SILC_PACKET_NEW_ID packet where it will receive
+the ID it will be using in the SILC network. The connecting client cannot
+start normal SILC session (sending messages or commands) until it has
+received its ID. The ID's are always created by the server except
+for server to router connection where servers create their own ID's.
+
+
+.ti 0
+3.1 Connection Auth Payload
+
+Client sends this payload to authenticate itself to the server. Server
+connecting to another server also sends this payload. Server receiving
+this payload MUST verify all the data in it and if something is to fail
+the authentication MUST be failed by sending SILC_PACKET_FAILURE packet.
+
+The payload may only be sent with SILC_PACKET_CONNECTION_AUTH packet.
+It MUST NOT be sent in any other packet type. The following diagram
+represent the Connection Auth Payload.
+
+
+.in 5
+.nf
+ 1 2 3
+ 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
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Payload Length | Connection Type |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| |
+~ Authentication Data ~
+| |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+.in 3
+
+.ce
+Figure 3: Connection Auth Payload
+
+
+.in 6
+o Payload Length (2 bytes) - Length of the entire Connection
+ Auth Payload.
+
+o Connection Type (2 bytes) - Indicates the type of the
+ connection. See section Connection Auth Request Payload
+ in [SILC2] for the list of connection types. This field MUST
+ include valid connection type or the packet MUST be discarded
+ and authentication MUST be failed.
+
+o Authentication Data (variable length) - The actual
+ authentication data. Contents of this depends on the
+ authentication method known by both parties. If no
+ authentication is required this field does not exist.
+.in 3
+
+
+.ti 0
+3.2 Connection Authentication Types
+
+SILC supports two authentication types to be used in the connection
+authentication protocol; passphrase or public key based authentication.
+The following sections defines the authentication methods. See [SILC2]
+for defined numerical authentication method types.
+
+
+.ti 0
+3.2.1 Passphrase Authentication
+
+Passphrase authentication or pre-shared-key based authentication is
+simply an authentication where the party that wants to authenticate
+itself to the other end sends the passphrase that is required by
+the other end, for example server.
+
+If the passphrase matches with the one in the server's end the
+authentication is successful. Otherwise SILC_PACKET_FAILURE MUST be
+sent to the sender and the protocol execution fails.
+
+This is REQUIRED authentication method to be supported by all SILC
+implementations.
+
+
+.ti 0
+3.2.2 Public Key Authentication
+
+Public key authentication may be used if passphrase based authentication
+is not desired. The public key authentication works by sending a
+signature as authentication data to the other end, say, server. The
+server MUST then verify the signature by the public key of the sender,
+which the server has received earlier in SKE protocol.
+
+The signature is computed using the private key of the sender by signing
+the HASH value provided by the SKE protocol previously, and the Key
+Exchange Start Payload from SKE protocol that was sent to the server.
+The server MUST verify the data, thus it must keep the HASH and the
+Key Exchange Start Payload saved during SKE and authentication protocols.
+
+If the verified signature matches the sent signature, the authentication
+were successful and SILC_PACKET_SUCCESS is sent. If it failed the protocol
+execution is stopped and SILC_PACKET_FAILURE is sent.
+
+This is REQUIRED authentication method to be supported by all SILC
+implementations.
+
+
+.ti 0
+3.3 Connection Authentication Status Types
+
+This section defines all connection authentication status types that
+may be returned in the SILC_PACKET_SUCCESS or SILC_PACKET_FAILURE packets
+to indicate the status of the protocol. Implementations may map the
+status types to human readable error message. All types except the
+SILC_AUTH_STATUS_OK type MUST be sent in SILC_PACKET_FAILURE packet.
+The length of status is 32 bits (4 bytes). The following status types
+are defined:
+
+
+
+0 SILC_AUTH_OK
+
+ Protocol was executed successfully.
+
+
+1 SILC_AUTH_FAILED
+
+ Authentication failed.
+
+
+.ti 0
+4 Security Considerations
+
+Security is central to the design of this protocol, and these security
+considerations permeate the specification. Common security considerations
+such as keeping private keys truly private and using adequate lengths for
+symmetric and asymmetric keys must be followed in order to maintain the
+security of this protocol.
+
+
+.ti 0
+5 References
+
+[SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC),
+ Protocol Specification", Internet Draft, April 2001.
+
+[SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft,
+ April 2001.
+
+[SILC4] Riikonen, P., "SILC Commands", Internet Draft, April 2001.
+
+[IRC] Oikarinen, J., and Reed D., "Internet Relay Chat Protocol",
+ RFC 1459, May 1993.
+
+[IRC-ARCH] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
+ April 2000.
+
+[IRC-CHAN] Kalt, C., "Internet Relay Chat: Channel Management", RFC
+ 2811, April 2000.
+
+[IRC-CLIENT] Kalt, C., "Internet Relay Chat: Client Protocol", RFC
+ 2812, April 2000.
+
+[IRC-SERVER] Kalt, C., "Internet Relay Chat: Server Protocol", RFC
+ 2813, April 2000.
+
+[SSH-TRANS] Ylonen, T., et al, "SSH Transport Layer Protocol",
+ Internet Draft.
+
+[PGP] Callas, J., et al, "OpenPGP Message Format", RFC 2440,
+ November 1998.
+
+[SPKI] Ellison C., et al, "SPKI Certificate Theory", RFC 2693,
+ September 1999.
+
+[PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
+ Infrastructure, Certificate and CRL Profile", RFC 2459,
+ January 1999.
+
+[Schneier] Schneier, B., "Applied Cryptography Second Edition",
+ John Wiley & Sons, New York, NY, 1996.
+
+[Menezes] Menezes, A., et al, "Handbook of Applied Cryptography",
+ CRC Press 1997.
+
+[OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol",
+ RFC 2412, November 1998.
+
+[ISAKMP] Maughan D., et al, "Internet Security Association and
+ Key Management Protocol (ISAKMP)", RFC 2408, November
+ 1998.
+
+[IKE] Harkins D., and Carrel D., "The Internet Key Exchange
+ (IKE)", RFC 2409, November 1998.
+
+[HMAC] Krawczyk, H., "HMAC: Keyed-Hashing for Message
+ Authentication", RFC 2104, February 1997.
+
+[PKCS1] Kalinski, B., and Staddon, J., "PKCS #1 RSA Cryptography
+ Specifications, Version 2.0", RFC 2437, October 1998.
+
+[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+
+.ti 0
+6 Author's Address
+
+.nf
+Pekka Riikonen
+Snellmanninkatu 34 A 15
+70100 Kuopio
+Finland
+
+EMail: priikone@silcnet.org
+
+This Internet-Draft expires XXX
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