diff --git a/ssh/cipher.go b/ssh/cipher.go index 99441395..f2ba1176 100644 --- a/ssh/cipher.go +++ b/ssh/cipher.go @@ -56,78 +56,78 @@ func newRC4(key, iv []byte) (cipher.Stream, error) { return rc4.NewCipher(key) } -type streamCipherMode struct { - keySize int - ivSize int - skip int - createFunc func(key, iv []byte) (cipher.Stream, error) +type cipherMode struct { + keySize int + ivSize int + create func(key, iv []byte, macKey []byte, algs directionAlgorithms) (packetCipher, error) } -func (c *streamCipherMode) createStream(key, iv []byte) (cipher.Stream, error) { - if len(key) < c.keySize { - panic("ssh: key length too small for cipher") - } - if len(iv) < c.ivSize { - panic("ssh: iv too small for cipher") - } - - stream, err := c.createFunc(key[:c.keySize], iv[:c.ivSize]) - if err != nil { - return nil, err - } - - var streamDump []byte - if c.skip > 0 { - streamDump = make([]byte, 512) - } - - for remainingToDump := c.skip; remainingToDump > 0; { - dumpThisTime := remainingToDump - if dumpThisTime > len(streamDump) { - dumpThisTime = len(streamDump) +func streamCipherMode(skip int, createFunc func(key, iv []byte) (cipher.Stream, error)) func(key, iv []byte, macKey []byte, algs directionAlgorithms) (packetCipher, error) { + return func(key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) { + stream, err := createFunc(key, iv) + if err != nil { + return nil, err } - stream.XORKeyStream(streamDump[:dumpThisTime], streamDump[:dumpThisTime]) - remainingToDump -= dumpThisTime - } - return stream, nil + var streamDump []byte + if skip > 0 { + streamDump = make([]byte, 512) + } + + for remainingToDump := skip; remainingToDump > 0; { + dumpThisTime := remainingToDump + if dumpThisTime > len(streamDump) { + dumpThisTime = len(streamDump) + } + stream.XORKeyStream(streamDump[:dumpThisTime], streamDump[:dumpThisTime]) + remainingToDump -= dumpThisTime + } + + mac := macModes[algs.MAC].new(macKey) + return &streamPacketCipher{ + mac: mac, + etm: macModes[algs.MAC].etm, + macResult: make([]byte, mac.Size()), + cipher: stream, + }, nil + } } // cipherModes documents properties of supported ciphers. Ciphers not included // are not supported and will not be negotiated, even if explicitly requested in // ClientConfig.Crypto.Ciphers. -var cipherModes = map[string]*streamCipherMode{ +var cipherModes = map[string]*cipherMode{ // Ciphers from RFC4344, which introduced many CTR-based ciphers. Algorithms // are defined in the order specified in the RFC. - "aes128-ctr": {16, aes.BlockSize, 0, newAESCTR}, - "aes192-ctr": {24, aes.BlockSize, 0, newAESCTR}, - "aes256-ctr": {32, aes.BlockSize, 0, newAESCTR}, + "aes128-ctr": {16, aes.BlockSize, streamCipherMode(0, newAESCTR)}, + "aes192-ctr": {24, aes.BlockSize, streamCipherMode(0, newAESCTR)}, + "aes256-ctr": {32, aes.BlockSize, streamCipherMode(0, newAESCTR)}, // Ciphers from RFC4345, which introduces security-improved arcfour ciphers. // They are defined in the order specified in the RFC. - "arcfour128": {16, 0, 1536, newRC4}, - "arcfour256": {32, 0, 1536, newRC4}, + "arcfour128": {16, 0, streamCipherMode(1536, newRC4)}, + "arcfour256": {32, 0, streamCipherMode(1536, newRC4)}, // Cipher defined in RFC 4253, which describes SSH Transport Layer Protocol. // Note that this cipher is not safe, as stated in RFC 4253: "Arcfour (and // RC4) has problems with weak keys, and should be used with caution." // RFC4345 introduces improved versions of Arcfour. - "arcfour": {16, 0, 0, newRC4}, + "arcfour": {16, 0, streamCipherMode(0, newRC4)}, - // AEAD ciphers are special cased. If we add any more non-stream - // ciphers, we should create a cleaner way to do this. - gcmCipherID: {16, 12, 0, nil}, - chacha20Poly1305ID: {64, 0, 0, nil}, + // AEAD ciphers + gcmCipherID: {16, 12, newGCMCipher}, + chacha20Poly1305ID: {64, 0, newChaCha20Cipher}, // CBC mode is insecure and so is not included in the default config. // (See http://www.isg.rhul.ac.uk/~kp/SandPfinal.pdf). If absolutely // needed, it's possible to specify a custom Config to enable it. // You should expect that an active attacker can recover plaintext if // you do. - aes128cbcID: {16, aes.BlockSize, 0, nil}, + aes128cbcID: {16, aes.BlockSize, newAESCBCCipher}, - // 3des-cbc is insecure and is disabled by default. - tripledescbcID: {24, des.BlockSize, 0, nil}, + // 3des-cbc is insecure and is not included in the default + // config. + tripledescbcID: {24, des.BlockSize, newTripleDESCBCCipher}, } // prefixLen is the length of the packet prefix that contains the packet length @@ -307,7 +307,7 @@ type gcmCipher struct { buf []byte } -func newGCMCipher(iv, key []byte) (packetCipher, error) { +func newGCMCipher(key, iv, unusedMacKey []byte, unusedAlgs directionAlgorithms) (packetCipher, error) { c, err := aes.NewCipher(key) if err != nil { return nil, err @@ -425,7 +425,7 @@ type cbcCipher struct { oracleCamouflage uint32 } -func newCBCCipher(c cipher.Block, iv, key, macKey []byte, algs directionAlgorithms) (packetCipher, error) { +func newCBCCipher(c cipher.Block, key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) { cbc := &cbcCipher{ mac: macModes[algs.MAC].new(macKey), decrypter: cipher.NewCBCDecrypter(c, iv), @@ -439,13 +439,13 @@ func newCBCCipher(c cipher.Block, iv, key, macKey []byte, algs directionAlgorith return cbc, nil } -func newAESCBCCipher(iv, key, macKey []byte, algs directionAlgorithms) (packetCipher, error) { +func newAESCBCCipher(key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) { c, err := aes.NewCipher(key) if err != nil { return nil, err } - cbc, err := newCBCCipher(c, iv, key, macKey, algs) + cbc, err := newCBCCipher(c, key, iv, macKey, algs) if err != nil { return nil, err } @@ -453,13 +453,13 @@ func newAESCBCCipher(iv, key, macKey []byte, algs directionAlgorithms) (packetCi return cbc, nil } -func newTripleDESCBCCipher(iv, key, macKey []byte, algs directionAlgorithms) (packetCipher, error) { +func newTripleDESCBCCipher(key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) { c, err := des.NewTripleDESCipher(key) if err != nil { return nil, err } - cbc, err := newCBCCipher(c, iv, key, macKey, algs) + cbc, err := newCBCCipher(c, key, iv, macKey, algs) if err != nil { return nil, err } @@ -646,9 +646,9 @@ type chacha20Poly1305Cipher struct { buf []byte } -func newChaCha20Cipher(key []byte) (packetCipher, error) { +func newChaCha20Cipher(key, unusedIV, unusedMACKey []byte, unusedAlgs directionAlgorithms) (packetCipher, error) { if len(key) != 64 { - panic("key length") + panic(len(key)) } c := &chacha20Poly1305Cipher{ diff --git a/ssh/transport.go b/ssh/transport.go index 5a567539..f6fae1db 100644 --- a/ssh/transport.go +++ b/ssh/transport.go @@ -233,51 +233,22 @@ var ( clientKeys = direction{[]byte{'A'}, []byte{'C'}, []byte{'E'}} ) -// generateKeys generates key material for IV, MAC and encryption. -func generateKeys(d direction, algs directionAlgorithms, kex *kexResult) (iv, key, macKey []byte) { - cipherMode := cipherModes[algs.Cipher] - macMode := macModes[algs.MAC] - - iv = make([]byte, cipherMode.ivSize) - key = make([]byte, cipherMode.keySize) - macKey = make([]byte, macMode.keySize) - - generateKeyMaterial(iv, d.ivTag, kex) - generateKeyMaterial(key, d.keyTag, kex) - generateKeyMaterial(macKey, d.macKeyTag, kex) - return -} - // setupKeys sets the cipher and MAC keys from kex.K, kex.H and sessionId, as // described in RFC 4253, section 6.4. direction should either be serverKeys // (to setup server->client keys) or clientKeys (for client->server keys). func newPacketCipher(d direction, algs directionAlgorithms, kex *kexResult) (packetCipher, error) { - iv, key, macKey := generateKeys(d, algs, kex) + cipherMode := cipherModes[algs.Cipher] + macMode := macModes[algs.MAC] - switch algs.Cipher { - case chacha20Poly1305ID: - return newChaCha20Cipher(key) - case gcmCipherID: - return newGCMCipher(iv, key) - case aes128cbcID: - return newAESCBCCipher(iv, key, macKey, algs) - case tripledescbcID: - return newTripleDESCBCCipher(iv, key, macKey, algs) - } + iv := make([]byte, cipherMode.ivSize) + key := make([]byte, cipherMode.keySize) + macKey := make([]byte, macMode.keySize) - c := &streamPacketCipher{ - mac: macModes[algs.MAC].new(macKey), - etm: macModes[algs.MAC].etm, - } - c.macResult = make([]byte, c.mac.Size()) + generateKeyMaterial(iv, d.ivTag, kex) + generateKeyMaterial(key, d.keyTag, kex) + generateKeyMaterial(macKey, d.macKeyTag, kex) - var err error - c.cipher, err = cipherModes[algs.Cipher].createStream(key, iv) - if err != nil { - return nil, err - } - - return c, nil + return cipherModes[algs.Cipher].create(key, iv, macKey, algs) } // generateKeyMaterial fills out with key material generated from tag, K, H