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authorGustav Simonsson <gustav.simonsson@gmail.com>2015-04-03 00:15:58 +0800
committerGustav Simonsson <gustav.simonsson@gmail.com>2015-05-12 23:18:30 +0800
commit6b23094cff77d7e485e0a2ae5698884f63c87ce7 (patch)
tree54f1b48de9df3cd7b6e8e388b91fa76190d1a852 /crypto
parent9918b6c84e2547f3d24a6cfeb97cfcbd6cb4dc98 (diff)
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Improve key store passphrase crypto
* Change MAC-then-Encrypt to Encrypt-then-MAC * Change AES256 to AES128 * Use first 16 bytes of KDF derived key for AES and remaining 16 for MAC
Diffstat (limited to 'crypto')
-rw-r--r--crypto/crypto.go2
-rw-r--r--crypto/key.go1
-rw-r--r--crypto/key_store_passphrase.go49
-rw-r--r--crypto/key_store_test.go2
4 files changed, 31 insertions, 23 deletions
diff --git a/crypto/crypto.go b/crypto/crypto.go
index 3c5783014..6fc5bfd36 100644
--- a/crypto/crypto.go
+++ b/crypto/crypto.go
@@ -252,7 +252,7 @@ func aesCBCDecrypt(key []byte, cipherText []byte, iv []byte) (plainText []byte,
decrypter.CryptBlocks(paddedPlainText, cipherText)
plainText = PKCS7Unpad(paddedPlainText)
if plainText == nil {
- err = errors.New("Decryption failed: PKCS7Unpad failed after decryption")
+ err = errors.New("Decryption failed: PKCS7Unpad failed after AES decryption")
}
return plainText, err
}
diff --git a/crypto/key.go b/crypto/key.go
index 0b84bfec1..654d9e83d 100644
--- a/crypto/key.go
+++ b/crypto/key.go
@@ -48,6 +48,7 @@ type plainKeyJSON struct {
}
type cipherJSON struct {
+ MAC []byte
Salt []byte
IV []byte
CipherText []byte
diff --git a/crypto/key_store_passphrase.go b/crypto/key_store_passphrase.go
index ee383584c..4cfb1851b 100644
--- a/crypto/key_store_passphrase.go
+++ b/crypto/key_store_passphrase.go
@@ -28,24 +28,25 @@ the private key is encrypted and on disk uses another JSON encoding.
Cryptography:
-1. Encryption key is scrypt derived key from user passphrase. Scrypt parameters
+1. Encryption key is first 16 bytes of SHA3-256 of first 16 bytes of
+ scrypt derived key from user passphrase. Scrypt parameters
(work factors) [1][2] are defined as constants below.
-2. Scrypt salt is 32 random bytes from CSPRNG. It is appended to ciphertext.
-3. Checksum is SHA3 of the private key bytes.
-4. Plaintext is concatenation of private key bytes and checksum.
-5. Encryption algo is AES 256 CBC [3][4]
-6. CBC IV is 16 random bytes from CSPRNG. It is appended to ciphertext.
+2. Scrypt salt is 32 random bytes from CSPRNG.
+ It's stored in plain next to ciphertext in key file.
+3. MAC is SHA3-256 of concatenation of ciphertext and last 16 bytes of scrypt derived key.
+4. Plaintext is the EC private key bytes.
+5. Encryption algo is AES 128 CBC [3][4]
+6. CBC IV is 16 random bytes from CSPRNG.
+ It's stored in plain next to ciphertext in key file.
7. Plaintext padding is PKCS #7 [5][6]
Encoding:
-1. On disk, ciphertext, salt and IV are encoded in a nested JSON object.
+1. On disk, the ciphertext, MAC, salt and IV are encoded in a nested JSON object.
cat a key file to see the structure.
2. byte arrays are base64 JSON strings.
3. The EC private key bytes are in uncompressed form [7].
They are a big-endian byte slice of the absolute value of D [8][9].
-4. The checksum is the last 32 bytes of the plaintext byte array and the
- private key is the preceeding bytes.
References:
@@ -124,21 +125,25 @@ func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) {
return err
}
+ encryptKey := Sha3(derivedKey[:16])[:16]
+
keyBytes := FromECDSA(key.PrivateKey)
- keyBytesHash := Sha3(keyBytes)
- toEncrypt := PKCS7Pad(append(keyBytes, keyBytesHash...))
+ toEncrypt := PKCS7Pad(keyBytes)
- AES256Block, err := aes.NewCipher(derivedKey)
+ AES128Block, err := aes.NewCipher(encryptKey)
if err != nil {
return err
}
iv := randentropy.GetEntropyCSPRNG(aes.BlockSize) // 16
- AES256CBCEncrypter := cipher.NewCBCEncrypter(AES256Block, iv)
+ AES128CBCEncrypter := cipher.NewCBCEncrypter(AES128Block, iv)
cipherText := make([]byte, len(toEncrypt))
- AES256CBCEncrypter.CryptBlocks(cipherText, toEncrypt)
+ AES128CBCEncrypter.CryptBlocks(cipherText, toEncrypt)
+
+ mac := Sha3(derivedKey[16:32], cipherText)
cipherStruct := cipherJSON{
+ mac,
salt,
iv,
cipherText,
@@ -177,6 +182,7 @@ func DecryptKey(ks keyStorePassphrase, keyAddr []byte, auth string) (keyBytes []
err = json.Unmarshal(fileContent, keyProtected)
keyId = keyProtected.Id
+ mac := keyProtected.Crypto.MAC
salt := keyProtected.Crypto.Salt
iv := keyProtected.Crypto.IV
cipherText := keyProtected.Crypto.CipherText
@@ -186,15 +192,16 @@ func DecryptKey(ks keyStorePassphrase, keyAddr []byte, auth string) (keyBytes []
if err != nil {
return nil, nil, err
}
- plainText, err := aesCBCDecrypt(derivedKey, cipherText, iv)
- if err != nil {
+
+ calculatedMAC := Sha3(derivedKey[16:32], cipherText)
+ if !bytes.Equal(calculatedMAC, mac) {
+ err = errors.New("Decryption failed: MAC mismatch")
return nil, nil, err
}
- keyBytes = plainText[:len(plainText)-32]
- keyBytesHash := plainText[len(plainText)-32:]
- if !bytes.Equal(Sha3(keyBytes), keyBytesHash) {
- err = errors.New("Decryption failed: checksum mismatch")
+
+ plainText, err := aesCBCDecrypt(Sha3(derivedKey[:16])[:16], cipherText, iv)
+ if err != nil {
return nil, nil, err
}
- return keyBytes, keyId, err
+ return plainText, keyId, err
}
diff --git a/crypto/key_store_test.go b/crypto/key_store_test.go
index f0a1e567b..6e50afe34 100644
--- a/crypto/key_store_test.go
+++ b/crypto/key_store_test.go
@@ -1,8 +1,8 @@
package crypto
import (
- "github.com/ethereum/go-ethereum/crypto/randentropy"
"github.com/ethereum/go-ethereum/common"
+ "github.com/ethereum/go-ethereum/crypto/randentropy"
"reflect"
"testing"
)