ssh/test: reset the random source before capturing a recording

If a recording file exists but is invalid for any reason, the random
source may have already been used, resulting in a recording that
cannot be replayed.

Change-Id: Ib81aaf163f5783fede2c14a0ac10a8d2af6019c6
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/664917
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Nicola Murino <nicola.murino@gmail.com>

ssh/test/recording_client_test.go

@@ -21,7 +21,6 @@ import (
 	"time"
 
 	"golang.org/x/crypto/internal/testenv"
-	"golang.org/x/crypto/sha3"
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/testdata"
 )
@@ -169,6 +168,8 @@ func (test *clientTest) run(t *testing.T, write bool) {
 	var clientConn net.Conn
 	var recordingConn *recordingConn
 
+	setDeterministicRandomSource(&test.config.Config)
+
 	if write {
 		// We store the username used when we record the connection so we can
 		// reuse the same username when running tests.
@@ -238,7 +239,6 @@ func recordingsClientConfig() *ssh.ClientConfig {
 	if config.KeyExchanges[0] == "mlkem768x25519-sha256" {
 		config.KeyExchanges = config.KeyExchanges[1:]
 	}
-	config.Rand = sha3.NewShake128()
 	config.Auth = []ssh.AuthMethod{
 		ssh.PublicKeys(testSigners["rsa"]),
 	}

ssh/test/recording_server_test.go

@@ -18,7 +18,6 @@ import (
 	"time"
 
 	"golang.org/x/crypto/internal/testenv"
-	"golang.org/x/crypto/sha3"
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/testdata"
 )
@@ -132,6 +131,8 @@ func (test *serverTest) run(t *testing.T, write bool) {
 	var serverConn net.Conn
 	var recordingConn *recordingConn
 
+	setDeterministicRandomSource(&test.config.Config)
+
 	if write {
 		var err error
 		recordingConn, err = test.connFromCommand(t)
@@ -211,9 +212,6 @@ func (test *serverTest) run(t *testing.T, write bool) {
 
 func recordingsServerConfig() *ssh.ServerConfig {
 	config := &ssh.ServerConfig{
-		Config: ssh.Config{
-			Rand: sha3.NewShake128(),
-		},
 		PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
 			return nil, nil
 		},

ssh/test/recording_test.go

@@ -23,6 +23,7 @@ import (
 	"text/template"
 	"time"
 
+	"golang.org/x/crypto/sha3"
 	"golang.org/x/crypto/ssh"
 )
 
@@ -412,6 +413,15 @@ func writeFile(path string, contents []byte) {
 	}
 }
 
+// setDeterministicRandomSource sets a deterministic random source for the
+// provided ssh.Config. It is intended solely for use in test cases, as
+// deterministic randomness is insecure and should never be used in production
+// environments. A deterministic random source is required to enable consistent
+// testing against recorded session files.
+func setDeterministicRandomSource(config *ssh.Config) {
+	config.Rand = sha3.NewShake128()
+}
+
 func TestMain(m *testing.M) {
 	flag.Usage = func() {
 		fmt.Fprintf(flag.CommandLine.Output(), "Usage of %s:\n", os.Args)