ssh: Add support for RSA keys stored in OpenSSH's new format

Adds support for parsing RSA keys in the openssh-key-v1 private key format.

Change-Id: Iacdcbaadf72413e4067d146203604fb50b780083
Reviewed-on: https://go-review.googlesource.com/35244
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
Reviewed-by: Paul Querna <paul@querna.org>
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

ssh/keys.go

@@ -824,7 +824,7 @@ func ParseDSAPrivateKey(der []byte) (*dsa.PrivateKey, error) {
 
 // Implemented based on the documentation at
 // https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.key
-func parseOpenSSHPrivateKey(key []byte) (*ed25519.PrivateKey, error) {
+func parseOpenSSHPrivateKey(key []byte) (crypto.PrivateKey, error) {
 	magic := append([]byte("openssh-key-v1"), 0)
 	if !bytes.Equal(magic, key[0:len(magic)]) {
 		return nil, errors.New("ssh: invalid openssh private key format")
@@ -844,14 +844,15 @@ func parseOpenSSHPrivateKey(key []byte) (*ed25519.PrivateKey, error) {
 		return nil, err
 	}
 
+	if w.KdfName != "none" || w.CipherName != "none" {
+		return nil, errors.New("ssh: cannot decode encrypted private keys")
+	}
+
 	pk1 := struct {
 		Check1  uint32
 		Check2  uint32
 		Keytype string
-		Pub     []byte
-		Priv    []byte
-		Comment string
-		Pad     []byte `ssh:"rest"`
+		Rest    []byte `ssh:"rest"`
 	}{}
 
 	if err := Unmarshal(w.PrivKeyBlock, &pk1); err != nil {
@@ -862,24 +863,75 @@ func parseOpenSSHPrivateKey(key []byte) (*ed25519.PrivateKey, error) {
 		return nil, errors.New("ssh: checkint mismatch")
 	}
 
-	// we only handle ed25519 keys currently
-	if pk1.Keytype != KeyAlgoED25519 {
-		return nil, errors.New("ssh: unhandled key type")
-	}
+	// we only handle ed25519 and rsa keys currently
+	switch pk1.Keytype {
+	case KeyAlgoRSA:
+		// https://github.com/openssh/openssh-portable/blob/master/sshkey.c#L2760-L2773
+		key := struct {
+			N       *big.Int
+			E       *big.Int
+			D       *big.Int
+			Iqmp    *big.Int
+			P       *big.Int
+			Q       *big.Int
+			Comment string
+			Pad     []byte `ssh:"rest"`
+		}{}
+
+		if err := Unmarshal(pk1.Rest, &key); err != nil {
+			return nil, err
+		}
 
-	for i, b := range pk1.Pad {
-		if int(b) != i+1 {
-			return nil, errors.New("ssh: padding not as expected")
+		for i, b := range key.Pad {
+			if int(b) != i+1 {
+				return nil, errors.New("ssh: padding not as expected")
+			}
 		}
-	}
 
-	if len(pk1.Priv) != ed25519.PrivateKeySize {
-		return nil, errors.New("ssh: private key unexpected length")
-	}
+		pk := &rsa.PrivateKey{
+			PublicKey: rsa.PublicKey{
+				N: key.N,
+				E: int(key.E.Int64()),
+			},
+			D:      key.D,
+			Primes: []*big.Int{key.P, key.Q},
+		}
 
-	pk := ed25519.PrivateKey(make([]byte, ed25519.PrivateKeySize))
-	copy(pk, pk1.Priv)
-	return &pk, nil
+		if err := pk.Validate(); err != nil {
+			return nil, err
+		}
+
+		pk.Precompute()
+
+		return pk, nil
+	case KeyAlgoED25519:
+		key := struct {
+			Pub     []byte
+			Priv    []byte
+			Comment string
+			Pad     []byte `ssh:"rest"`
+		}{}
+
+		if err := Unmarshal(pk1.Rest, &key); err != nil {
+			return nil, err
+		}
+
+		if len(key.Priv) != ed25519.PrivateKeySize {
+			return nil, errors.New("ssh: private key unexpected length")
+		}
+
+		for i, b := range key.Pad {
+			if int(b) != i+1 {
+				return nil, errors.New("ssh: padding not as expected")
+			}
+		}
+
+		pk := ed25519.PrivateKey(make([]byte, ed25519.PrivateKeySize))
+		copy(pk, key.Priv)
+		return &pk, nil
+	default:
+		return nil, errors.New("ssh: unhandled key type")
+	}
 }
 
 // FingerprintLegacyMD5 returns the user presentation of the key's

ssh/testdata/keys.go

@@ -48,6 +48,22 @@ AAAEAaYmXltfW6nhRo3iWGglRB48lYq0z0Q3I3KyrdutEr6j7d/uFLuDlRbBc4ZVOsx+Gb
 HKuOrPtLHFvHsjWPwO+/AAAAE2dhcnRvbm1AZ2FydG9ubS14cHMBAg==
 -----END OPENSSH PRIVATE KEY-----
 `),
+	"rsa-openssh-format": []byte(`-----BEGIN OPENSSH PRIVATE KEY-----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+-----END OPENSSH PRIVATE KEY-----`),
 	"user": []byte(`-----BEGIN EC PRIVATE KEY-----
 MHcCAQEEILYCAeq8f7V4vSSypRw7pxy8yz3V5W4qg8kSC3zJhqpQoAoGCCqGSM49
 AwEHoUQDQgAEYcO2xNKiRUYOLEHM7VYAp57HNyKbOdYtHD83Z4hzNPVC4tM5mdGD