From d359caa4a39d59a440003b37a6cc7ace3871fd4a Mon Sep 17 00:00:00 2001 From: Mariano Cano Date: Fri, 7 Feb 2020 20:24:11 -0800 Subject: [PATCH] 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 TryBot-Result: Gopher Robot LUCI-TryBot-Result: Go LUCI Reviewed-by: Cherry Mui Reviewed-by: Roland Shoemaker Auto-Submit: Roland Shoemaker --- ssh/keys.go | 286 +++++++++++++++++++++++++++++++++++++++-------- ssh/keys_test.go | 68 +++++++++++ 2 files changed, 308 insertions(+), 46 deletions(-) diff --git a/ssh/keys.go b/ssh/keys.go index dac8ee7244..1bf28d87f6 100644 --- a/ssh/keys.go +++ b/ssh/keys.go @@ -13,11 +13,13 @@ import ( "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 @@ func MarshalAuthorizedKey(key PublicKey) []byte { 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 passphraseProtectedOpenSSHKey(passphrase []byte) openSSHDecryptFunc { } } +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):] - - var w struct { - CipherName string - KdfName string - KdfOpts string - NumKeys uint32 - PubKey []byte - PrivKeyBlock []byte - } + remaining := key[len(privateKeyAuthMagic):] + var w openSSHEncryptedPrivateKey if err := Unmarshal(remaining, &w); err != nil { return nil, err } @@ -1284,13 +1376,7 @@ func parseOpenSSHPrivateKey(key []byte, decrypt openSSHDecryptFunc) (crypto.Priv 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 @@ func parseOpenSSHPrivateKey(key []byte, decrypt openSSHDecryptFunc) (crypto.Priv 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 @@ func parseOpenSSHPrivateKey(key []byte, decrypt openSSHDecryptFunc) (crypto.Priv 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 @@ func parseOpenSSHPrivateKey(key []byte, decrypt openSSHDecryptFunc) (crypto.Priv 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 parseOpenSSHPrivateKey(key []byte, decrypt openSSHDecryptFunc) (crypto.Priv } } +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 @@ func checkOpenSSHKeyPadding(pad []byte) error { 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 334ef74532..a8e216ede8 100644 --- a/ssh/keys_test.go +++ b/ssh/keys_test.go @@ -281,6 +281,74 @@ func TestMarshalParsePublicKey(t *testing.T) { } } +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