ssh: add diffie-hellman-group16-sha512 kex

This group is disabled by default because it is a bit slower than
the others.
The group18-sha512 variant is too slow to include.

Benchstat results including diffie-hellman-group18-sha512:

name                                           time/op
Kexes/diffie-hellman-group-exchange-sha256-12  22.6ms ± 9%
Kexes/diffie-hellman-group18-sha512-12          1.15s ±11%
Kexes/ecdh-sha2-nistp384-12                    3.91ms ± 6%
Kexes/ecdh-sha2-nistp256-12                     304µs ± 5%
Kexes/curve25519-sha256@libssh.org-12           413µs ± 7%
Kexes/ecdh-sha2-nistp521-12                    11.6ms ±13%
Kexes/curve25519-sha256-12                      361µs ± 5%
Kexes/diffie-hellman-group-exchange-sha1-12    22.9ms ± 9%
Kexes/diffie-hellman-group1-sha1-12            3.59ms ± 6%
Kexes/diffie-hellman-group14-sha1-12           22.1ms ±11%
Kexes/diffie-hellman-group14-sha256-12         21.6ms ± 8%
Kexes/diffie-hellman-group16-sha512-12          138ms ± 9%

name                                           alloc/op
Kexes/diffie-hellman-group-exchange-sha256-12  67.8kB ± 1%
Kexes/diffie-hellman-group18-sha512-12          243kB ± 9%
Kexes/ecdh-sha2-nistp384-12                    13.9kB ± 0%
Kexes/ecdh-sha2-nistp256-12                    12.1kB ± 0%
Kexes/curve25519-sha256@libssh.org-12          8.22kB ± 0%
Kexes/ecdh-sha2-nistp521-12                    16.5kB ± 0%
Kexes/curve25519-sha256-12                     8.22kB ± 0%
Kexes/diffie-hellman-group-exchange-sha1-12    67.5kB ± 0%
Kexes/diffie-hellman-group1-sha1-12            34.9kB ± 0%
Kexes/diffie-hellman-group14-sha1-12           61.9kB ± 0%
Kexes/diffie-hellman-group14-sha256-12         62.0kB ± 0%
Kexes/diffie-hellman-group16-sha512-12          117kB ± 0%

name                                           allocs/op
Kexes/diffie-hellman-group-exchange-sha256-12     314 ± 0%
Kexes/diffie-hellman-group18-sha512-12            271 ± 4%
Kexes/ecdh-sha2-nistp384-12                       243 ± 0%
Kexes/ecdh-sha2-nistp256-12                       213 ± 0%
Kexes/curve25519-sha256@libssh.org-12             168 ± 0%
Kexes/ecdh-sha2-nistp521-12                       245 ± 0%
Kexes/curve25519-sha256-12                        168 ± 0%
Kexes/diffie-hellman-group-exchange-sha1-12       314 ± 0%
Kexes/diffie-hellman-group1-sha1-12               255 ± 0%
Kexes/diffie-hellman-group14-sha1-12              255 ± 0%
Kexes/diffie-hellman-group14-sha256-12            255 ± 0%
Kexes/diffie-hellman-group16-sha512-12            256 ± 0%

Change-Id: Id119401fda7e417675325f37e3d442e70585206c
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/506839
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>

1 files changed, 41 insertions, 0 deletions

diff --git a/ssh/kex_test.go b/ssh/kex_test.go
index 327013b..cb7f66a 100644
--- a/ssh/kex_test.go
+++ b/ssh/kex_test.go
@@ -8,6 +8,7 @@ package ssh
 
 import (
 	"crypto/rand"
+	"fmt"
 	"reflect"
 	"sync"
 	"testing"
@@ -63,3 +64,43 @@ func TestKexes(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkKexes(b *testing.B) {
+	type kexResultErr struct {
+		result *kexResult
+		err    error
+	}
+
+	for name, kex := range kexAlgoMap {
+		b.Run(name, func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				t1, t2 := memPipe()
+
+				s := make(chan kexResultErr, 1)
+				c := make(chan kexResultErr, 1)
+				var magics handshakeMagics
+
+				go func() {
+					r, e := kex.Client(t1, rand.Reader, &magics)
+					t1.Close()
+					c <- kexResultErr{r, e}
+				}()
+				go func() {
+					r, e := kex.Server(t2, rand.Reader, &magics, testSigners["ecdsa"].(AlgorithmSigner), testSigners["ecdsa"].PublicKey().Type())
+					t2.Close()
+					s <- kexResultErr{r, e}
+				}()
+
+				clientRes := <-c
+				serverRes := <-s
+
+				if clientRes.err != nil {
+					panic(fmt.Sprintf("client: %v", clientRes.err))
+				}
+				if serverRes.err != nil {
+					panic(fmt.Sprintf("server: %v", serverRes.err))
+				}
+			}
+		})
+	}
+}