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ssh: add diffie-hellman-group16-sha512 kex
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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/[email protected]           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/[email protected]          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/[email protected]             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 <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Auto-Submit: Filippo Valsorda <[email protected]>
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Filippo Valsorda <[email protected]>
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drakkan authored and gopherbot committed Jul 31, 2023
1 parent ddfa821 commit eab9315
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Showing 4 changed files with 61 additions and 3 deletions.
8 changes: 5 additions & 3 deletions ssh/common.go
Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,8 @@ 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,
kexAlgoDH14SHA256, kexAlgoDH14SHA1, kexAlgoDH1SHA1,
kexAlgoDH14SHA256, kexAlgoDH16SHA512, kexAlgoDH14SHA1,
kexAlgoDH1SHA1,
}

// serverForbiddenKexAlgos contains key exchange algorithms, that are forbidden
Expand All @@ -59,8 +60,9 @@ var serverForbiddenKexAlgos = map[string]struct{}{
kexAlgoDHGEXSHA256: {}, // server half implementation is only minimal to satisfy the automated tests
}

// preferredKexAlgos specifies the default preference for key-exchange algorithms
// in preference order.
// preferredKexAlgos specifies the default preference for key-exchange
// algorithms in preference order. The diffie-hellman-group16-sha512 algorithm
// is disabled by default because it is a bit slower than the others.
var preferredKexAlgos = []string{
kexAlgoCurve25519SHA256, kexAlgoCurve25519SHA256LibSSH,
kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521,
Expand Down
12 changes: 12 additions & 0 deletions ssh/kex.go
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ const (
kexAlgoDH1SHA1 = "diffie-hellman-group1-sha1"
kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1"
kexAlgoDH14SHA256 = "diffie-hellman-group14-sha256"
kexAlgoDH16SHA512 = "diffie-hellman-group16-sha512"
kexAlgoECDH256 = "ecdh-sha2-nistp256"
kexAlgoECDH384 = "ecdh-sha2-nistp384"
kexAlgoECDH521 = "ecdh-sha2-nistp521"
Expand Down Expand Up @@ -430,6 +431,17 @@ func init() {
hashFunc: crypto.SHA256,
}

// This is the group called diffie-hellman-group16-sha512 in RFC
// 8268 and Oakley Group 16 in RFC 3526.
p, _ = new(big.Int).SetString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

kexAlgoMap[kexAlgoDH16SHA512] = &dhGroup{
g: new(big.Int).SetInt64(2),
p: p,
pMinus1: new(big.Int).Sub(p, bigOne),
hashFunc: crypto.SHA512,
}

kexAlgoMap[kexAlgoECDH521] = &ecdh{elliptic.P521()}
kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()}
kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()}
Expand Down
41 changes: 41 additions & 0 deletions ssh/kex_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ package ssh

import (
"crypto/rand"
"fmt"
"reflect"
"sync"
"testing"
Expand Down Expand Up @@ -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))
}
}
})
}
}
3 changes: 3 additions & 0 deletions ssh/test/session_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -410,6 +410,9 @@ func TestKeyExchanges(t *testing.T) {
// are not included in the default list of supported kex so we have to add them
// here manually.
kexOrder = append(kexOrder, "diffie-hellman-group-exchange-sha1", "diffie-hellman-group-exchange-sha256")
// The key exchange algorithms diffie-hellman-group16-sha512 is disabled by
// default so we add it here manually.
kexOrder = append(kexOrder, "diffie-hellman-group16-sha512")
for _, kex := range kexOrder {
t.Run(kex, func(t *testing.T) {
server := newServer(t)
Expand Down

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