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 <nicola.murino@gmail.com>
Change-Id: Id4ce345a2065840f193986739ea890f105a1e929
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/392014
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
diff --git a/ssh/common.go b/ssh/common.go
index ba7052b..9dda7e5 100644
--- a/ssh/common.go
+++ b/ssh/common.go
@@ -48,7 +48,7 @@
// 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 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 36eac6c..1a098a2 100644
--- a/ssh/kex.go
+++ b/ssh/kex.go
@@ -22,6 +22,7 @@
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 @@
// 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) 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 @@
return nil, err
}
- h := hashFunc.New()
+ h := group.hashFunc.New()
magics.write(h)
writeString(h, kexDHReply.HostKey)
writeInt(h, X)
@@ -147,12 +147,11 @@
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 @@
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 @@
K: K,
HostKey: hostKeyBytes,
Signature: sig,
- Hash: crypto.SHA1,
+ Hash: group.hashFunc,
}, err
}
@@ -388,23 +387,33 @@
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),
+ hashFunc: crypto.SHA1,
+ }
+
+ // 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("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB9ED529077096966D670C354E4ABC9804F1746C08CA18217C32905E462E36CE3BE39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9DE2BCBF6955817183995497CEA956AE515D2261898FA051015728E5A8AACAA68FFFFFFFFFFFFFFFF", 16)
+ group14 := &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),
+ 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()}
