ssh: add hmac-sha2-512

This adds support for hmac-sha2-512 to ensure compatibility with SSH clients that request this MAC algorithm.

This rebases #18.

Change-Id: Ia103c10a8b7e2e8dde556d5c36550eb5fa6bc1f6
GitHub-Last-Rev: 987ccae
GitHub-Pull-Request: #257
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/501455
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Commit-Queue: Han-Wen Nienhuys <hanwen@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

ssh/common.go

@@ -85,7 +85,7 @@ var supportedHostKeyAlgos = []string{
 // This is based on RFC 4253, section 6.4, but with hmac-md5 variants removed
 // because they have reached the end of their useful life.
 var supportedMACs = []string{
-	"hmac-sha2-512-etm@openssh.com", "hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1", "hmac-sha1-96",
+	"hmac-sha2-512-etm@openssh.com", "hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha2-512", "hmac-sha1", "hmac-sha1-96",
 }
 
 var supportedCompressions = []string{compressionNone}

ssh/mac.go

@@ -53,6 +53,9 @@ var macModes = map[string]*macMode{
 	"hmac-sha2-256-etm@openssh.com": {32, true, func(key []byte) hash.Hash {
 		return hmac.New(sha256.New, key)
 	}},
+	"hmac-sha2-512": {64, false, func(key []byte) hash.Hash {
+		return hmac.New(sha512.New, key)
+	}},
 	"hmac-sha2-256": {32, false, func(key []byte) hash.Hash {
 		return hmac.New(sha256.New, key)
 	}},