From f653fd44571b05e38b7310e56b69d111e09bdd2f Mon Sep 17 00:00:00 2001 From: Filippo Valsorda Date: Sat, 12 Mar 2022 10:21:59 -0500 Subject: [PATCH] ssh: add diffie-hellman-group14-sha256 kex RFC 9142 made diffie-hellman-group14-sha256 from RFC 8268 a MUST, and it's strictly better than diffie-hellman-group14-sha1, which we already have, and trivial to add. > The method of key exchange used for the name "diffie-hellman- > group14-sha256" is the same as that for "diffie-hellman-group14-sha1" > except that the SHA256 hash algorithm is used. Ignore the bigger groups which have a meaningful performance cost, and don't share the same interoperability benefit. Adapted from CL 387994. Fixes golang/go#31731 Co-authored-by: Nicola Murino Change-Id: Id4ce345a2065840f193986739ea890f105a1e929 --- ssh/common.go | 4 ++-- ssh/kex.go | 41 +++++++++++++++++++++++++---------------- 2 files changed, 27 insertions(+), 18 deletions(-) diff --git a/ssh/common.go b/ssh/common.go index ba7052b0be..9dda7e5fad 100644 --- a/ssh/common.go +++ b/ssh/common.go @@ -48,7 +48,7 @@ var supportedKexAlgos = []string{ // P384 and P521 are not constant-time yet, but since we don't // reuse ephemeral keys, using them for ECDH should be OK. kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521, - kexAlgoDH14SHA1, kexAlgoDH1SHA1, + kexAlgoDH14SHA256, kexAlgoDH14SHA1, kexAlgoDH1SHA1, } // serverForbiddenKexAlgos contains key exchange algorithms, that are forbidden @@ -63,7 +63,7 @@ var serverForbiddenKexAlgos = map[string]struct{}{ var preferredKexAlgos = []string{ kexAlgoCurve25519SHA256, kexAlgoCurve25519SHA256LibSSH, kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521, - kexAlgoDH14SHA1, + kexAlgoDH14SHA256, kexAlgoDH14SHA1, } // supportedHostKeyAlgos specifies the supported host-key algorithms (i.e. methods diff --git a/ssh/kex.go b/ssh/kex.go index 36eac6cacd..1a098a2559 100644 --- a/ssh/kex.go +++ b/ssh/kex.go @@ -22,6 +22,7 @@ import ( const ( kexAlgoDH1SHA1 = "diffie-hellman-group1-sha1" kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1" + kexAlgoDH14SHA256 = "diffie-hellman-group14-sha256" kexAlgoECDH256 = "ecdh-sha2-nistp256" kexAlgoECDH384 = "ecdh-sha2-nistp384" kexAlgoECDH521 = "ecdh-sha2-nistp521" @@ -87,6 +88,7 @@ type kexAlgorithm interface { // dhGroup is a multiplicative group suitable for implementing Diffie-Hellman key agreement. type dhGroup struct { g, p, pMinus1 *big.Int + hashFunc crypto.Hash } func (group *dhGroup) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) { @@ -97,8 +99,6 @@ func (group *dhGroup) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, } func (group *dhGroup) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) { - hashFunc := crypto.SHA1 - var x *big.Int for { var err error @@ -133,7 +133,7 @@ func (group *dhGroup) Client(c packetConn, randSource io.Reader, magics *handsha return nil, err } - h := hashFunc.New() + h := group.hashFunc.New() magics.write(h) writeString(h, kexDHReply.HostKey) writeInt(h, X) @@ -147,12 +147,11 @@ func (group *dhGroup) Client(c packetConn, randSource io.Reader, magics *handsha K: K, HostKey: kexDHReply.HostKey, Signature: kexDHReply.Signature, - Hash: crypto.SHA1, + Hash: group.hashFunc, }, 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 @@ -180,7 +179,7 @@ func (group *dhGroup) Server(c packetConn, randSource io.Reader, magics *handsha hostKeyBytes := priv.PublicKey().Marshal() - h := hashFunc.New() + h := group.hashFunc.New() magics.write(h) writeString(h, hostKeyBytes) writeInt(h, kexDHInit.X) @@ -212,7 +211,7 @@ func (group *dhGroup) Server(c packetConn, randSource io.Reader, magics *handsha K: K, HostKey: hostKeyBytes, Signature: sig, - Hash: crypto.SHA1, + Hash: group.hashFunc, }, err } @@ -388,25 +387,35 @@ func (kex *ecdh) Server(c packetConn, rand io.Reader, magics *handshakeMagics, p 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. + // 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), + g: new(big.Int).SetInt64(2), + p: p, + pMinus1: new(big.Int).Sub(p, bigOne), + hashFunc: crypto.SHA1, } - // This is the group called diffie-hellman-group14-sha1 in RFC - // 4253 and Oakley Group 14 in RFC 3526. + // This are the groups called diffie-hellman-group14-sha1 and + // diffie-hellman-group14-sha256 in RFC 4253 and RFC 8268, + // and Oakley Group 14 in RFC 3526. p, _ = new(big.Int).SetString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kexAlgoMap[kexAlgoDH14SHA1] = &dhGroup{ + group14 := &dhGroup{ g: new(big.Int).SetInt64(2), p: p, pMinus1: new(big.Int).Sub(p, bigOne), } + kexAlgoMap[kexAlgoDH14SHA1] = &dhGroup{ + g: group14.g, p: group14.p, pMinus1: group14.pMinus1, + hashFunc: crypto.SHA1, + } + kexAlgoMap[kexAlgoDH14SHA256] = &dhGroup{ + g: group14.g, p: group14.p, pMinus1: group14.pMinus1, + hashFunc: crypto.SHA256, + } + kexAlgoMap[kexAlgoECDH521] = &ecdh{elliptic.P521()} kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()} kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()}