diff options
Diffstat (limited to 'vendor/golang.org/x/crypto/ssh/kex.go')
| -rw-r--r-- | vendor/golang.org/x/crypto/ssh/kex.go | 789 |
1 files changed, 789 insertions, 0 deletions
diff --git a/vendor/golang.org/x/crypto/ssh/kex.go b/vendor/golang.org/x/crypto/ssh/kex.go new file mode 100644 index 000000000..6c3c648fc --- /dev/null +++ b/vendor/golang.org/x/crypto/ssh/kex.go @@ -0,0 +1,789 @@ +// Copyright 2013 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package ssh + +import ( + "crypto" + "crypto/ecdsa" + "crypto/elliptic" + "crypto/rand" + "crypto/subtle" + "encoding/binary" + "errors" + "fmt" + "io" + "math/big" + + "golang.org/x/crypto/curve25519" +) + +const ( + kexAlgoDH1SHA1 = "diffie-hellman-group1-sha1" + kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1" + kexAlgoECDH256 = "ecdh-sha2-nistp256" + kexAlgoECDH384 = "ecdh-sha2-nistp384" + kexAlgoECDH521 = "ecdh-sha2-nistp521" + kexAlgoCurve25519SHA256 = "curve25519-sha256@libssh.org" + + // For the following kex only the client half contains a production + // ready implementation. The server half only consists of a minimal + // implementation to satisfy the automated tests. + kexAlgoDHGEXSHA1 = "diffie-hellman-group-exchange-sha1" + kexAlgoDHGEXSHA256 = "diffie-hellman-group-exchange-sha256" +) + +// kexResult captures the outcome of a key exchange. +type kexResult struct { + // Session hash. See also RFC 4253, section 8. + H []byte + + // Shared secret. See also RFC 4253, section 8. + K []byte + + // Host key as hashed into H. + HostKey []byte + + // Signature of H. + Signature []byte + + // A cryptographic hash function that matches the security + // level of the key exchange algorithm. It is used for + // calculating H, and for deriving keys from H and K. + Hash crypto.Hash + + // The session ID, which is the first H computed. This is used + // to derive key material inside the transport. + SessionID []byte +} + +// handshakeMagics contains data that is always included in the +// session hash. +type handshakeMagics struct { + clientVersion, serverVersion []byte + clientKexInit, serverKexInit []byte +} + +func (m *handshakeMagics) write(w io.Writer) { + writeString(w, m.clientVersion) + writeString(w, m.serverVersion) + writeString(w, m.clientKexInit) + writeString(w, m.serverKexInit) +} + +// kexAlgorithm abstracts different key exchange algorithms. +type kexAlgorithm interface { + // Server runs server-side key agreement, signing the result + // with a hostkey. + Server(p packetConn, rand io.Reader, magics *handshakeMagics, s Signer) (*kexResult, error) + + // Client runs the client-side key agreement. Caller is + // responsible for verifying the host key signature. + Client(p packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) +} + +// dhGroup is a multiplicative group suitable for implementing Diffie-Hellman key agreement. +type dhGroup struct { + g, p, pMinus1 *big.Int +} + +func (group *dhGroup) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) { + if theirPublic.Cmp(bigOne) <= 0 || theirPublic.Cmp(group.pMinus1) >= 0 { + return nil, errors.New("ssh: DH parameter out of bounds") + } + return new(big.Int).Exp(theirPublic, myPrivate, group.p), nil +} + +func (group *dhGroup) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) { + hashFunc := crypto.SHA1 + + var x *big.Int + for { + var err error + if x, err = rand.Int(randSource, group.pMinus1); err != nil { + return nil, err + } + if x.Sign() > 0 { + break + } + } + + X := new(big.Int).Exp(group.g, x, group.p) + kexDHInit := kexDHInitMsg{ + X: X, + } + if err := c.writePacket(Marshal(&kexDHInit)); err != nil { + return nil, err + } + + packet, err := c.readPacket() + if err != nil { + return nil, err + } + + var kexDHReply kexDHReplyMsg + if err = Unmarshal(packet, &kexDHReply); err != nil { + return nil, err + } + + ki, err := group.diffieHellman(kexDHReply.Y, x) + if err != nil { + return nil, err + } + + h := hashFunc.New() + magics.write(h) + writeString(h, kexDHReply.HostKey) + writeInt(h, X) + writeInt(h, kexDHReply.Y) + K := make([]byte, intLength(ki)) + marshalInt(K, ki) + h.Write(K) + + return &kexResult{ + H: h.Sum(nil), + K: K, + HostKey: kexDHReply.HostKey, + Signature: kexDHReply.Signature, + Hash: crypto.SHA1, + }, nil +} + +func (group *dhGroup) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) { + hashFunc := crypto.SHA1 + packet, err := c.readPacket() + if err != nil { + return + } + var kexDHInit kexDHInitMsg + if err = Unmarshal(packet, &kexDHInit); err != nil { + return + } + + var y *big.Int + for { + if y, err = rand.Int(randSource, group.pMinus1); err != nil { + return + } + if y.Sign() > 0 { + break + } + } + + Y := new(big.Int).Exp(group.g, y, group.p) + ki, err := group.diffieHellman(kexDHInit.X, y) + if err != nil { + return nil, err + } + + hostKeyBytes := priv.PublicKey().Marshal() + + h := hashFunc.New() + magics.write(h) + writeString(h, hostKeyBytes) + writeInt(h, kexDHInit.X) + writeInt(h, Y) + + K := make([]byte, intLength(ki)) + marshalInt(K, ki) + h.Write(K) + + H := h.Sum(nil) + + // H is already a hash, but the hostkey signing will apply its + // own key-specific hash algorithm. + sig, err := signAndMarshal(priv, randSource, H) + if err != nil { + return nil, err + } + + kexDHReply := kexDHReplyMsg{ + HostKey: hostKeyBytes, + Y: Y, + Signature: sig, + } + packet = Marshal(&kexDHReply) + + err = c.writePacket(packet) + return &kexResult{ + H: H, + K: K, + HostKey: hostKeyBytes, + Signature: sig, + Hash: crypto.SHA1, + }, err +} + +// ecdh performs Elliptic Curve Diffie-Hellman key exchange as +// described in RFC 5656, section 4. +type ecdh struct { + curve elliptic.Curve +} + +func (kex *ecdh) Client(c packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) { + ephKey, err := ecdsa.GenerateKey(kex.curve, rand) + if err != nil { + return nil, err + } + + kexInit := kexECDHInitMsg{ + ClientPubKey: elliptic.Marshal(kex.curve, ephKey.PublicKey.X, ephKey.PublicKey.Y), + } + + serialized := Marshal(&kexInit) + if err := c.writePacket(serialized); err != nil { + return nil, err + } + + packet, err := c.readPacket() + if err != nil { + return nil, err + } + + var reply kexECDHReplyMsg + if err = Unmarshal(packet, &reply); err != nil { + return nil, err + } + + x, y, err := unmarshalECKey(kex.curve, reply.EphemeralPubKey) + if err != nil { + return nil, err + } + + // generate shared secret + secret, _ := kex.curve.ScalarMult(x, y, ephKey.D.Bytes()) + + h := ecHash(kex.curve).New() + magics.write(h) + writeString(h, reply.HostKey) + writeString(h, kexInit.ClientPubKey) + writeString(h, reply.EphemeralPubKey) + K := make([]byte, intLength(secret)) + marshalInt(K, secret) + h.Write(K) + + return &kexResult{ + H: h.Sum(nil), + K: K, + HostKey: reply.HostKey, + Signature: reply.Signature, + Hash: ecHash(kex.curve), + }, nil +} + +// unmarshalECKey parses and checks an EC key. +func unmarshalECKey(curve elliptic.Curve, pubkey []byte) (x, y *big.Int, err error) { + x, y = elliptic.Unmarshal(curve, pubkey) + if x == nil { + return nil, nil, errors.New("ssh: elliptic.Unmarshal failure") + } + if !validateECPublicKey(curve, x, y) { + return nil, nil, errors.New("ssh: public key not on curve") + } + return x, y, nil +} + +// validateECPublicKey checks that the point is a valid public key for +// the given curve. See [SEC1], 3.2.2 +func validateECPublicKey(curve elliptic.Curve, x, y *big.Int) bool { + if x.Sign() == 0 && y.Sign() == 0 { + return false + } + + if x.Cmp(curve.Params().P) >= 0 { + return false + } + + if y.Cmp(curve.Params().P) >= 0 { + return false + } + + if !curve.IsOnCurve(x, y) { + return false + } + + // We don't check if N * PubKey == 0, since + // + // - the NIST curves have cofactor = 1, so this is implicit. + // (We don't foresee an implementation that supports non NIST + // curves) + // + // - for ephemeral keys, we don't need to worry about small + // subgroup attacks. + return true +} + +func (kex *ecdh) Server(c packetConn, rand io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) { + packet, err := c.readPacket() + if err != nil { + return nil, err + } + + var kexECDHInit kexECDHInitMsg + if err = Unmarshal(packet, &kexECDHInit); err != nil { + return nil, err + } + + clientX, clientY, err := unmarshalECKey(kex.curve, kexECDHInit.ClientPubKey) + if err != nil { + return nil, err + } + + // We could cache this key across multiple users/multiple + // connection attempts, but the benefit is small. OpenSSH + // generates a new key for each incoming connection. + ephKey, err := ecdsa.GenerateKey(kex.curve, rand) + if err != nil { + return nil, err + } + + hostKeyBytes := priv.PublicKey().Marshal() + + serializedEphKey := elliptic.Marshal(kex.curve, ephKey.PublicKey.X, ephKey.PublicKey.Y) + + // generate shared secret + secret, _ := kex.curve.ScalarMult(clientX, clientY, ephKey.D.Bytes()) + + h := ecHash(kex.curve).New() + magics.write(h) + writeString(h, hostKeyBytes) + writeString(h, kexECDHInit.ClientPubKey) + writeString(h, serializedEphKey) + + K := make([]byte, intLength(secret)) + marshalInt(K, secret) + h.Write(K) + + H := h.Sum(nil) + + // H is already a hash, but the hostkey signing will apply its + // own key-specific hash algorithm. + sig, err := signAndMarshal(priv, rand, H) + if err != nil { + return nil, err + } + + reply := kexECDHReplyMsg{ + EphemeralPubKey: serializedEphKey, + HostKey: hostKeyBytes, + Signature: sig, + } + + serialized := Marshal(&reply) + if err := c.writePacket(serialized); err != nil { + return nil, err + } + + return &kexResult{ + H: H, + K: K, + HostKey: reply.HostKey, + Signature: sig, + Hash: ecHash(kex.curve), + }, nil +} + +var kexAlgoMap = map[string]kexAlgorithm{} + +func init() { + // This is the group called diffie-hellman-group1-sha1 in RFC + // 4253 and Oakley Group 2 in RFC 2409. + p, _ := new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF", 16) + kexAlgoMap[kexAlgoDH1SHA1] = &dhGroup{ + g: new(big.Int).SetInt64(2), + p: p, + pMinus1: new(big.Int).Sub(p, bigOne), + } + + // This is the group called diffie-hellman-group14-sha1 in RFC + // 4253 and Oakley Group 14 in RFC 3526. + p, _ = new(big.Int).SetString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kexAlgoMap[kexAlgoDH14SHA1] = &dhGroup{ + g: new(big.Int).SetInt64(2), + p: p, + pMinus1: new(big.Int).Sub(p, bigOne), + } + + kexAlgoMap[kexAlgoECDH521] = &ecdh{elliptic.P521()} + kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()} + kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()} + kexAlgoMap[kexAlgoCurve25519SHA256] = &curve25519sha256{} + kexAlgoMap[kexAlgoDHGEXSHA1] = &dhGEXSHA{hashFunc: crypto.SHA1} + kexAlgoMap[kexAlgoDHGEXSHA256] = &dhGEXSHA{hashFunc: crypto.SHA256} +} + +// curve25519sha256 implements the curve25519-sha256@libssh.org key +// agreement protocol, as described in +// https://git.libssh.org/projects/libssh.git/tree/doc/curve25519-sha256@libssh.org.txt +type curve25519sha256 struct{} + +type curve25519KeyPair struct { + priv [32]byte + pub [32]byte +} + +func (kp *curve25519KeyPair) generate(rand io.Reader) error { + if _, err := io.ReadFull(rand, kp.priv[:]); err != nil { + return err + } + curve25519.ScalarBaseMult(&kp.pub, &kp.priv) + return nil +} + +// curve25519Zeros is just an array of 32 zero bytes so that we have something +// convenient to compare against in order to reject curve25519 points with the +// wrong order. +var curve25519Zeros [32]byte + +func (kex *curve25519sha256) Client(c packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) { + var kp curve25519KeyPair + if err := kp.generate(rand); err != nil { + return nil, err + } + if err := c.writePacket(Marshal(&kexECDHInitMsg{kp.pub[:]})); err != nil { + return nil, err + } + + packet, err := c.readPacket() + if err != nil { + return nil, err + } + + var reply kexECDHReplyMsg + if err = Unmarshal(packet, &reply); err != nil { + return nil, err + } + if len(reply.EphemeralPubKey) != 32 { + return nil, errors.New("ssh: peer's curve25519 public value has wrong length") + } + + var servPub, secret [32]byte + copy(servPub[:], reply.EphemeralPubKey) + curve25519.ScalarMult(&secret, &kp.priv, &servPub) + if subtle.ConstantTimeCompare(secret[:], curve25519Zeros[:]) == 1 { + return nil, errors.New("ssh: peer's curve25519 public value has wrong order") + } + + h := crypto.SHA256.New() + magics.write(h) + writeString(h, reply.HostKey) + writeString(h, kp.pub[:]) + writeString(h, reply.EphemeralPubKey) + + ki := new(big.Int).SetBytes(secret[:]) + K := make([]byte, intLength(ki)) + marshalInt(K, ki) + h.Write(K) + + return &kexResult{ + H: h.Sum(nil), + K: K, + HostKey: reply.HostKey, + Signature: reply.Signature, + Hash: crypto.SHA256, + }, nil +} + +func (kex *curve25519sha256) Server(c packetConn, rand io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) { + packet, err := c.readPacket() + if err != nil { + return + } + var kexInit kexECDHInitMsg + if err = Unmarshal(packet, &kexInit); err != nil { + return + } + + if len(kexInit.ClientPubKey) != 32 { + return nil, errors.New("ssh: peer's curve25519 public value has wrong length") + } + + var kp curve25519KeyPair + if err := kp.generate(rand); err != nil { + return nil, err + } + + var clientPub, secret [32]byte + copy(clientPub[:], kexInit.ClientPubKey) + curve25519.ScalarMult(&secret, &kp.priv, &clientPub) + if subtle.ConstantTimeCompare(secret[:], curve25519Zeros[:]) == 1 { + return nil, errors.New("ssh: peer's curve25519 public value has wrong order") + } + + hostKeyBytes := priv.PublicKey().Marshal() + + h := crypto.SHA256.New() + magics.write(h) + writeString(h, hostKeyBytes) + writeString(h, kexInit.ClientPubKey) + writeString(h, kp.pub[:]) + + ki := new(big.Int).SetBytes(secret[:]) + K := make([]byte, intLength(ki)) + marshalInt(K, ki) + h.Write(K) + + H := h.Sum(nil) + + sig, err := signAndMarshal(priv, rand, H) + if err != nil { + return nil, err + } + + reply := kexECDHReplyMsg{ + EphemeralPubKey: kp.pub[:], + HostKey: hostKeyBytes, + Signature: sig, + } + if err := c.writePacket(Marshal(&reply)); err != nil { + return nil, err + } + return &kexResult{ + H: H, + K: K, + HostKey: hostKeyBytes, + Signature: sig, + Hash: crypto.SHA256, + }, nil +} + +// dhGEXSHA implements the diffie-hellman-group-exchange-sha1 and +// diffie-hellman-group-exchange-sha256 key agreement protocols, +// as described in RFC 4419 +type dhGEXSHA struct { + g, p *big.Int + hashFunc crypto.Hash +} + +const numMRTests = 64 + +const ( + dhGroupExchangeMinimumBits = 2048 + dhGroupExchangePreferredBits = 2048 + dhGroupExchangeMaximumBits = 8192 +) + +func (gex *dhGEXSHA) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) { + if theirPublic.Sign() <= 0 || theirPublic.Cmp(gex.p) >= 0 { + return nil, fmt.Errorf("ssh: DH parameter out of bounds") + } + return new(big.Int).Exp(theirPublic, myPrivate, gex.p), nil +} + +func (gex *dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) { + // Send GexRequest + kexDHGexRequest := kexDHGexRequestMsg{ + MinBits: dhGroupExchangeMinimumBits, + PreferedBits: dhGroupExchangePreferredBits, + MaxBits: dhGroupExchangeMaximumBits, + } + if err := c.writePacket(Marshal(&kexDHGexRequest)); err != nil { + return nil, err + } + + // Receive GexGroup + packet, err := c.readPacket() + if err != nil { + return nil, err + } + + var kexDHGexGroup kexDHGexGroupMsg + if err = Unmarshal(packet, &kexDHGexGroup); err != nil { + return nil, err + } + + // reject if p's bit length < dhGroupExchangeMinimumBits or > dhGroupExchangeMaximumBits + if kexDHGexGroup.P.BitLen() < dhGroupExchangeMinimumBits || kexDHGexGroup.P.BitLen() > dhGroupExchangeMaximumBits { + return nil, fmt.Errorf("ssh: server-generated gex p is out of range (%d bits)", kexDHGexGroup.P.BitLen()) + } + + gex.p = kexDHGexGroup.P + gex.g = kexDHGexGroup.G + + // Check if p is safe by verifing that p and (p-1)/2 are primes + one := big.NewInt(1) + var pHalf = &big.Int{} + pHalf.Rsh(gex.p, 1) + if !gex.p.ProbablyPrime(numMRTests) || !pHalf.ProbablyPrime(numMRTests) { + return nil, fmt.Errorf("ssh: server provided gex p is not safe") + } + + // Check if g is safe by verifing that g > 1 and g < p - 1 + var pMinusOne = &big.Int{} + pMinusOne.Sub(gex.p, one) + if gex.g.Cmp(one) != 1 && gex.g.Cmp(pMinusOne) != -1 { + return nil, fmt.Errorf("ssh: server provided gex g is not safe") + } + + // Send GexInit + x, err := rand.Int(randSource, pHalf) + if err != nil { + return nil, err + } + X := new(big.Int).Exp(gex.g, x, gex.p) + kexDHGexInit := kexDHGexInitMsg{ + X: X, + } + if err := c.writePacket(Marshal(&kexDHGexInit)); err != nil { + return nil, err + } + + // Receive GexReply + packet, err = c.readPacket() + if err != nil { + return nil, err + } + + var kexDHGexReply kexDHGexReplyMsg + if err = Unmarshal(packet, &kexDHGexReply); err != nil { + return nil, err + } + + kInt, err := gex.diffieHellman(kexDHGexReply.Y, x) + if err != nil { + return nil, err + } + + // Check if k is safe by verifing that k > 1 and k < p - 1 + if kInt.Cmp(one) != 1 && kInt.Cmp(pMinusOne) != -1 { + return nil, fmt.Errorf("ssh: derived k is not safe") + } + + h := gex.hashFunc.New() + magics.write(h) + writeString(h, kexDHGexReply.HostKey) + binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits)) + binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits)) + binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits)) + writeInt(h, gex.p) + writeInt(h, gex.g) + writeInt(h, X) + writeInt(h, kexDHGexReply.Y) + K := make([]byte, intLength(kInt)) + marshalInt(K, kInt) + h.Write(K) + + return &kexResult{ + H: h.Sum(nil), + K: K, + HostKey: kexDHGexReply.HostKey, + Signature: kexDHGexReply.Signature, + Hash: gex.hashFunc, + }, nil +} + +// Server half implementation of the Diffie Hellman Key Exchange with SHA1 and SHA256. +// +// This is a minimal implementation to satisfy the automated tests. +func (gex *dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) { + // Receive GexRequest + packet, err := c.readPacket() + if err != nil { + return + } + var kexDHGexRequest kexDHGexRequestMsg + if err = Unmarshal(packet, &kexDHGexRequest); err != nil { + return + } + + // smoosh the user's preferred size into our own limits + if kexDHGexRequest.PreferedBits > dhGroupExchangeMaximumBits { + kexDHGexRequest.PreferedBits = dhGroupExchangeMaximumBits + } + if kexDHGexRequest.PreferedBits < dhGroupExchangeMinimumBits { + kexDHGexRequest.PreferedBits = dhGroupExchangeMinimumBits + } + // fix min/max if they're inconsistent. technically, we could just pout + // and hang up, but there's no harm in giving them the benefit of the + // doubt and just picking a bitsize for them. + if kexDHGexRequest.MinBits > kexDHGexRequest.PreferedBits { + kexDHGexRequest.MinBits = kexDHGexRequest.PreferedBits + } + if kexDHGexRequest.MaxBits < kexDHGexRequest.PreferedBits { + kexDHGexRequest.MaxBits = kexDHGexRequest.PreferedBits + } + + // Send GexGroup + // This is the group called diffie-hellman-group14-sha1 in RFC + // 4253 and Oakley Group 14 in RFC 3526. + p, _ := new(big.Int).SetString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gex.p = p + gex.g = big.NewInt(2) + + kexDHGexGroup := kexDHGexGroupMsg{ + P: gex.p, + G: gex.g, + } + if err := c.writePacket(Marshal(&kexDHGexGroup)); err != nil { + return nil, err + } + + // Receive GexInit + packet, err = c.readPacket() + if err != nil { + return + } + var kexDHGexInit kexDHGexInitMsg + if err = Unmarshal(packet, &kexDHGexInit); err != nil { + return + } + + var pHalf = &big.Int{} + pHalf.Rsh(gex.p, 1) + + y, err := rand.Int(randSource, pHalf) + if err != nil { + return + } + + Y := new(big.Int).Exp(gex.g, y, gex.p) + kInt, err := gex.diffieHellman(kexDHGexInit.X, y) + if err != nil { + return nil, err + } + + hostKeyBytes := priv.PublicKey().Marshal() + + h := gex.hashFunc.New() + magics.write(h) + writeString(h, hostKeyBytes) + binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits)) + binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits)) + binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits)) + writeInt(h, gex.p) + writeInt(h, gex.g) + writeInt(h, kexDHGexInit.X) + writeInt(h, Y) + + K := make([]byte, intLength(kInt)) + marshalInt(K, kInt) + h.Write(K) + + H := h.Sum(nil) + + // H is already a hash, but the hostkey signing will apply its + // own key-specific hash algorithm. + sig, err := signAndMarshal(priv, randSource, H) + if err != nil { + return nil, err + } + + kexDHGexReply := kexDHGexReplyMsg{ + HostKey: hostKeyBytes, + Y: Y, + Signature: sig, + } + packet = Marshal(&kexDHGexReply) + + err = c.writePacket(packet) + + return &kexResult{ + H: H, + K: K, + HostKey: hostKeyBytes, + Signature: sig, + Hash: gex.hashFunc, + }, err +} |