ssh: support for marshaling keys using the OpenSSH format
This adds methods to marshal private keys, encrypted and unencrypted
to the OpenSSH format.
Fixes golang/go#37132
Change-Id: I1a95301f789ce04858e6b147748c6e8b7700384b
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/218620
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>
diff --git a/ssh/keys.go b/ssh/keys.go
index dac8ee7..1bf28d8 100644
--- a/ssh/keys.go
+++ b/ssh/keys.go
@@ -13,11 +13,13 @@
"crypto/ecdsa"
"crypto/elliptic"
"crypto/md5"
+ "crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/asn1"
"encoding/base64"
+ "encoding/binary"
"encoding/hex"
"encoding/pem"
"errors"
@@ -295,6 +297,18 @@
return b.Bytes()
}
+// MarshalPrivateKey returns a PEM block with the private key serialized in the
+// OpenSSH format.
+func MarshalPrivateKey(key crypto.PrivateKey, comment string) (*pem.Block, error) {
+ return marshalOpenSSHPrivateKey(key, comment, unencryptedOpenSSHMarshaler)
+}
+
+// MarshalPrivateKeyWithPassphrase returns a PEM block holding the encrypted
+// private key serialized in the OpenSSH format.
+func MarshalPrivateKeyWithPassphrase(key crypto.PrivateKey, comment string, passphrase []byte) (*pem.Block, error) {
+ return marshalOpenSSHPrivateKey(key, comment, passphraseProtectedOpenSSHMarshaler(passphrase))
+}
+
// PublicKey represents a public key using an unspecified algorithm.
//
// Some PublicKeys provided by this package also implement CryptoPublicKey.
@@ -1241,28 +1255,106 @@
}
}
+func unencryptedOpenSSHMarshaler(privKeyBlock []byte) ([]byte, string, string, string, error) {
+ key := generateOpenSSHPadding(privKeyBlock, 8)
+ return key, "none", "none", "", nil
+}
+
+func passphraseProtectedOpenSSHMarshaler(passphrase []byte) openSSHEncryptFunc {
+ return func(privKeyBlock []byte) ([]byte, string, string, string, error) {
+ salt := make([]byte, 16)
+ if _, err := rand.Read(salt); err != nil {
+ return nil, "", "", "", err
+ }
+
+ opts := struct {
+ Salt []byte
+ Rounds uint32
+ }{salt, 16}
+
+ // Derive key to encrypt the private key block.
+ k, err := bcrypt_pbkdf.Key(passphrase, salt, int(opts.Rounds), 32+aes.BlockSize)
+ if err != nil {
+ return nil, "", "", "", err
+ }
+
+ // Add padding matching the block size of AES.
+ keyBlock := generateOpenSSHPadding(privKeyBlock, aes.BlockSize)
+
+ // Encrypt the private key using the derived secret.
+
+ dst := make([]byte, len(keyBlock))
+ key, iv := k[:32], k[32:]
+ block, err := aes.NewCipher(key)
+ if err != nil {
+ return nil, "", "", "", err
+ }
+
+ stream := cipher.NewCTR(block, iv)
+ stream.XORKeyStream(dst, keyBlock)
+
+ return dst, "aes256-ctr", "bcrypt", string(Marshal(opts)), nil
+ }
+}
+
+const privateKeyAuthMagic = "openssh-key-v1\x00"
+
type openSSHDecryptFunc func(CipherName, KdfName, KdfOpts string, PrivKeyBlock []byte) ([]byte, error)
+type openSSHEncryptFunc func(PrivKeyBlock []byte) (ProtectedKeyBlock []byte, cipherName, kdfName, kdfOptions string, err error)
+
+type openSSHEncryptedPrivateKey struct {
+ CipherName string
+ KdfName string
+ KdfOpts string
+ NumKeys uint32
+ PubKey []byte
+ PrivKeyBlock []byte
+}
+
+type openSSHPrivateKey struct {
+ Check1 uint32
+ Check2 uint32
+ Keytype string
+ Rest []byte `ssh:"rest"`
+}
+
+type openSSHRSAPrivateKey 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"`
+}
+
+type openSSHEd25519PrivateKey struct {
+ Pub []byte
+ Priv []byte
+ Comment string
+ Pad []byte `ssh:"rest"`
+}
+
+type openSSHECDSAPrivateKey struct {
+ Curve string
+ Pub []byte
+ D *big.Int
+ Comment string
+ Pad []byte `ssh:"rest"`
+}
// parseOpenSSHPrivateKey parses an OpenSSH private key, using the decrypt
// function to unwrap the encrypted portion. unencryptedOpenSSHKey can be used
// as the decrypt function to parse an unencrypted private key. See
// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.key.
func parseOpenSSHPrivateKey(key []byte, decrypt openSSHDecryptFunc) (crypto.PrivateKey, error) {
- const magic = "openssh-key-v1\x00"
- if len(key) < len(magic) || string(key[:len(magic)]) != magic {
+ if len(key) < len(privateKeyAuthMagic) || string(key[:len(privateKeyAuthMagic)]) != privateKeyAuthMagic {
return nil, errors.New("ssh: invalid openssh private key format")
}
- remaining := key[len(magic):]
+ remaining := key[len(privateKeyAuthMagic):]
- var w struct {
- CipherName string
- KdfName string
- KdfOpts string
- NumKeys uint32
- PubKey []byte
- PrivKeyBlock []byte
- }
-
+ var w openSSHEncryptedPrivateKey
if err := Unmarshal(remaining, &w); err != nil {
return nil, err
}
@@ -1284,13 +1376,7 @@
return nil, err
}
- pk1 := struct {
- Check1 uint32
- Check2 uint32
- Keytype string
- Rest []byte `ssh:"rest"`
- }{}
-
+ var pk1 openSSHPrivateKey
if err := Unmarshal(privKeyBlock, &pk1); err != nil || pk1.Check1 != pk1.Check2 {
if w.CipherName != "none" {
return nil, x509.IncorrectPasswordError
@@ -1300,18 +1386,7 @@
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"`
- }{}
-
+ var key openSSHRSAPrivateKey
if err := Unmarshal(pk1.Rest, &key); err != nil {
return nil, err
}
@@ -1337,13 +1412,7 @@
return pk, nil
case KeyAlgoED25519:
- key := struct {
- Pub []byte
- Priv []byte
- Comment string
- Pad []byte `ssh:"rest"`
- }{}
-
+ var key openSSHEd25519PrivateKey
if err := Unmarshal(pk1.Rest, &key); err != nil {
return nil, err
}
@@ -1360,14 +1429,7 @@
copy(pk, key.Priv)
return &pk, nil
case KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521:
- key := struct {
- Curve string
- Pub []byte
- D *big.Int
- Comment string
- Pad []byte `ssh:"rest"`
- }{}
-
+ var key openSSHECDSAPrivateKey
if err := Unmarshal(pk1.Rest, &key); err != nil {
return nil, err
}
@@ -1415,6 +1477,131 @@
}
}
+func marshalOpenSSHPrivateKey(key crypto.PrivateKey, comment string, encrypt openSSHEncryptFunc) (*pem.Block, error) {
+ var w openSSHEncryptedPrivateKey
+ var pk1 openSSHPrivateKey
+
+ // Random check bytes.
+ var check uint32
+ if err := binary.Read(rand.Reader, binary.BigEndian, &check); err != nil {
+ return nil, err
+ }
+
+ pk1.Check1 = check
+ pk1.Check2 = check
+ w.NumKeys = 1
+
+ // Use a []byte directly on ed25519 keys.
+ if k, ok := key.(*ed25519.PrivateKey); ok {
+ key = *k
+ }
+
+ switch k := key.(type) {
+ case *rsa.PrivateKey:
+ E := new(big.Int).SetInt64(int64(k.PublicKey.E))
+ // Marshal public key:
+ // E and N are in reversed order in the public and private key.
+ pubKey := struct {
+ KeyType string
+ E *big.Int
+ N *big.Int
+ }{
+ KeyAlgoRSA,
+ E, k.PublicKey.N,
+ }
+ w.PubKey = Marshal(pubKey)
+
+ // Marshal private key.
+ key := openSSHRSAPrivateKey{
+ N: k.PublicKey.N,
+ E: E,
+ D: k.D,
+ Iqmp: k.Precomputed.Qinv,
+ P: k.Primes[0],
+ Q: k.Primes[1],
+ Comment: comment,
+ }
+ pk1.Keytype = KeyAlgoRSA
+ pk1.Rest = Marshal(key)
+ case ed25519.PrivateKey:
+ pub := make([]byte, ed25519.PublicKeySize)
+ priv := make([]byte, ed25519.PrivateKeySize)
+ copy(pub, k[32:])
+ copy(priv, k)
+
+ // Marshal public key.
+ pubKey := struct {
+ KeyType string
+ Pub []byte
+ }{
+ KeyAlgoED25519, pub,
+ }
+ w.PubKey = Marshal(pubKey)
+
+ // Marshal private key.
+ key := openSSHEd25519PrivateKey{
+ Pub: pub,
+ Priv: priv,
+ Comment: comment,
+ }
+ pk1.Keytype = KeyAlgoED25519
+ pk1.Rest = Marshal(key)
+ case *ecdsa.PrivateKey:
+ var curve, keyType string
+ switch name := k.Curve.Params().Name; name {
+ case "P-256":
+ curve = "nistp256"
+ keyType = KeyAlgoECDSA256
+ case "P-384":
+ curve = "nistp384"
+ keyType = KeyAlgoECDSA384
+ case "P-521":
+ curve = "nistp521"
+ keyType = KeyAlgoECDSA521
+ default:
+ return nil, errors.New("ssh: unhandled elliptic curve " + name)
+ }
+
+ pub := elliptic.Marshal(k.Curve, k.PublicKey.X, k.PublicKey.Y)
+
+ // Marshal public key.
+ pubKey := struct {
+ KeyType string
+ Curve string
+ Pub []byte
+ }{
+ keyType, curve, pub,
+ }
+ w.PubKey = Marshal(pubKey)
+
+ // Marshal private key.
+ key := openSSHECDSAPrivateKey{
+ Curve: curve,
+ Pub: pub,
+ D: k.D,
+ Comment: comment,
+ }
+ pk1.Keytype = keyType
+ pk1.Rest = Marshal(key)
+ default:
+ return nil, fmt.Errorf("ssh: unsupported key type %T", k)
+ }
+
+ var err error
+ // Add padding and encrypt the key if necessary.
+ w.PrivKeyBlock, w.CipherName, w.KdfName, w.KdfOpts, err = encrypt(Marshal(pk1))
+ if err != nil {
+ return nil, err
+ }
+
+ b := Marshal(w)
+ block := &pem.Block{
+ Type: "OPENSSH PRIVATE KEY",
+ Bytes: append([]byte(privateKeyAuthMagic), b...),
+ }
+ return block, nil
+}
+
func checkOpenSSHKeyPadding(pad []byte) error {
for i, b := range pad {
if int(b) != i+1 {
@@ -1424,6 +1611,13 @@
return nil
}
+func generateOpenSSHPadding(block []byte, blockSize int) []byte {
+ for i, l := 0, len(block); (l+i)%blockSize != 0; i++ {
+ block = append(block, byte(i+1))
+ }
+ return block
+}
+
// FingerprintLegacyMD5 returns the user presentation of the key's
// fingerprint as described by RFC 4716 section 4.
func FingerprintLegacyMD5(pubKey PublicKey) string {
diff --git a/ssh/keys_test.go b/ssh/keys_test.go
index 334ef74..a8e216e 100644
--- a/ssh/keys_test.go
+++ b/ssh/keys_test.go
@@ -281,6 +281,74 @@
}
}
+func TestMarshalPrivateKey(t *testing.T) {
+ tests := []struct {
+ name string
+ }{
+ {"rsa-openssh-format"},
+ {"ed25519"},
+ {"p256-openssh-format"},
+ {"p384-openssh-format"},
+ {"p521-openssh-format"},
+ }
+ for _, tt := range tests {
+ t.Run(tt.name, func(t *testing.T) {
+ expected, ok := testPrivateKeys[tt.name]
+ if !ok {
+ t.Fatalf("cannot find key %s", tt.name)
+ }
+
+ block, err := MarshalPrivateKey(expected, "test@golang.org")
+ if err != nil {
+ t.Fatalf("cannot marshal %s: %v", tt.name, err)
+ }
+
+ key, err := ParseRawPrivateKey(pem.EncodeToMemory(block))
+ if err != nil {
+ t.Fatalf("cannot parse %s: %v", tt.name, err)
+ }
+
+ if !reflect.DeepEqual(expected, key) {
+ t.Errorf("unexpected marshaled key %s", tt.name)
+ }
+ })
+ }
+}
+
+func TestMarshalPrivateKeyWithPassphrase(t *testing.T) {
+ tests := []struct {
+ name string
+ }{
+ {"rsa-openssh-format"},
+ {"ed25519"},
+ {"p256-openssh-format"},
+ {"p384-openssh-format"},
+ {"p521-openssh-format"},
+ }
+ for _, tt := range tests {
+ t.Run(tt.name, func(t *testing.T) {
+ expected, ok := testPrivateKeys[tt.name]
+ if !ok {
+ t.Fatalf("cannot find key %s", tt.name)
+ }
+
+ block, err := MarshalPrivateKeyWithPassphrase(expected, "test@golang.org", []byte("test-passphrase"))
+ if err != nil {
+ t.Fatalf("cannot marshal %s: %v", tt.name, err)
+ }
+
+ key, err := ParseRawPrivateKeyWithPassphrase(pem.EncodeToMemory(block), []byte("test-passphrase"))
+ if err != nil {
+ t.Fatalf("cannot parse %s: %v", tt.name, err)
+ }
+
+ if !reflect.DeepEqual(expected, key) {
+ t.Errorf("unexpected marshaled key %s", tt.name)
+ }
+ })
+ }
+}
+
type testAuthResult struct {
pubKey PublicKey
options []string
