diff --git a/ssh/kex.go b/ssh/kex.go index 1a098a2559..94287e44db 100644 --- a/ssh/kex.go +++ b/ssh/kex.go @@ -563,7 +563,6 @@ func (kex *curve25519sha256) Server(c packetConn, rand io.Reader, magics *handsh // diffie-hellman-group-exchange-sha256 key agreement protocols, // as described in RFC 4419 type dhGEXSHA struct { - g, p *big.Int hashFunc crypto.Hash } @@ -573,14 +572,7 @@ const ( 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) { +func (gex *dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) { // Send GexRequest kexDHGexRequest := kexDHGexRequestMsg{ MinBits: dhGroupExchangeMinimumBits, @@ -597,35 +589,29 @@ func (gex dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshake return nil, err } - var kexDHGexGroup kexDHGexGroupMsg - if err = Unmarshal(packet, &kexDHGexGroup); err != nil { + var msg kexDHGexGroupMsg + if err = Unmarshal(packet, &msg); 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()) + if msg.P.BitLen() < dhGroupExchangeMinimumBits || msg.P.BitLen() > dhGroupExchangeMaximumBits { + return nil, fmt.Errorf("ssh: server-generated gex p is out of range (%d bits)", msg.P.BitLen()) } - gex.p = kexDHGexGroup.P - gex.g = kexDHGexGroup.G - - // Check if g is safe by verifing that g > 1 and g < p - 1 - one := big.NewInt(1) - var pMinusOne = &big.Int{} - pMinusOne.Sub(gex.p, one) - if gex.g.Cmp(one) != 1 && gex.g.Cmp(pMinusOne) != -1 { + // Check if g is safe by verifying that 1 < g < p-1 + pMinusOne := new(big.Int).Sub(msg.P, bigOne) + if msg.G.Cmp(bigOne) <= 0 || msg.G.Cmp(pMinusOne) >= 0 { return nil, fmt.Errorf("ssh: server provided gex g is not safe") } // Send GexInit - var pHalf = &big.Int{} - pHalf.Rsh(gex.p, 1) + pHalf := new(big.Int).Rsh(msg.P, 1) x, err := rand.Int(randSource, pHalf) if err != nil { return nil, err } - X := new(big.Int).Exp(gex.g, x, gex.p) + X := new(big.Int).Exp(msg.G, x, msg.P) kexDHGexInit := kexDHGexInitMsg{ X: X, } @@ -644,13 +630,13 @@ func (gex dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshake return nil, err } - kInt, err := gex.diffieHellman(kexDHGexReply.Y, x) - if err != nil { - return nil, err + if kexDHGexReply.Y.Cmp(bigOne) <= 0 || kexDHGexReply.Y.Cmp(pMinusOne) >= 0 { + return nil, errors.New("ssh: DH parameter out of bounds") } + kInt := new(big.Int).Exp(kexDHGexReply.Y, x, msg.P) - // Check if k is safe by verifing that k > 1 and k < p - 1 - if kInt.Cmp(one) != 1 && kInt.Cmp(pMinusOne) != -1 { + // Check if k is safe by verifying that k > 1 and k < p - 1 + if kInt.Cmp(bigOne) <= 0 || kInt.Cmp(pMinusOne) >= 0 { return nil, fmt.Errorf("ssh: derived k is not safe") } @@ -660,8 +646,8 @@ func (gex dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshake 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, msg.P) + writeInt(h, msg.G) writeInt(h, X) writeInt(h, kexDHGexReply.Y) K := make([]byte, intLength(kInt)) @@ -691,35 +677,17 @@ func (gex dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshake 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) + g := big.NewInt(2) - kexDHGexGroup := kexDHGexGroupMsg{ - P: gex.p, - G: gex.g, + msg := &kexDHGexGroupMsg{ + P: p, + G: g, } - if err := c.writePacket(Marshal(&kexDHGexGroup)); err != nil { + if err := c.writePacket(Marshal(msg)); err != nil { return nil, err } @@ -733,19 +701,19 @@ func (gex dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshake return } - var pHalf = &big.Int{} - pHalf.Rsh(gex.p, 1) + pHalf := new(big.Int).Rsh(p, 1) y, err := rand.Int(randSource, pHalf) if err != nil { return } + Y := new(big.Int).Exp(g, y, p) - Y := new(big.Int).Exp(gex.g, y, gex.p) - kInt, err := gex.diffieHellman(kexDHGexInit.X, y) - if err != nil { - return nil, err + pMinusOne := new(big.Int).Sub(p, bigOne) + if kexDHGexInit.X.Cmp(bigOne) <= 0 || kexDHGexInit.X.Cmp(pMinusOne) >= 0 { + return nil, errors.New("ssh: DH parameter out of bounds") } + kInt := new(big.Int).Exp(kexDHGexInit.X, y, p) hostKeyBytes := priv.PublicKey().Marshal() @@ -755,8 +723,8 @@ func (gex dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshake 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, p) + writeInt(h, g) writeInt(h, kexDHGexInit.X) writeInt(h, Y)