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@ -28,24 +28,25 @@ the private key is encrypted and on disk uses another JSON encoding. |
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Cryptography: |
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1. Encryption key is scrypt derived key from user passphrase. Scrypt parameters |
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1. Encryption key is first 16 bytes of SHA3-256 of first 16 bytes of |
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scrypt derived key from user passphrase. Scrypt parameters |
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(work factors) [1][2] are defined as constants below. |
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2. Scrypt salt is 32 random bytes from CSPRNG. It is appended to ciphertext. |
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3. Checksum is SHA3 of the private key bytes. |
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4. Plaintext is concatenation of private key bytes and checksum. |
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5. Encryption algo is AES 256 CBC [3][4] |
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6. CBC IV is 16 random bytes from CSPRNG. It is appended to ciphertext. |
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2. Scrypt salt is 32 random bytes from CSPRNG. |
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It's stored in plain next to ciphertext in key file. |
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3. MAC is SHA3-256 of concatenation of ciphertext and last 16 bytes of scrypt derived key. |
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4. Plaintext is the EC private key bytes. |
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5. Encryption algo is AES 128 CBC [3][4] |
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6. CBC IV is 16 random bytes from CSPRNG. |
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It's stored in plain next to ciphertext in key file. |
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7. Plaintext padding is PKCS #7 [5][6] |
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Encoding: |
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1. On disk, ciphertext, salt and IV are encoded in a nested JSON object. |
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1. On disk, the ciphertext, MAC, salt and IV are encoded in a nested JSON object. |
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cat a key file to see the structure. |
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2. byte arrays are base64 JSON strings. |
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3. The EC private key bytes are in uncompressed form [7]. |
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They are a big-endian byte slice of the absolute value of D [8][9]. |
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4. The checksum is the last 32 bytes of the plaintext byte array and the |
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private key is the preceeding bytes. |
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References: |
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@ -75,11 +76,14 @@ import ( |
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"path/filepath" |
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"code.google.com/p/go-uuid/uuid" |
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"github.com/ethereum/go-ethereum/common" |
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"github.com/ethereum/go-ethereum/crypto/randentropy" |
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"golang.org/x/crypto/scrypt" |
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) |
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const ( |
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keyHeaderVersion = "1" |
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keyHeaderKDF = "scrypt" |
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// 2^18 / 8 / 1 uses 256MB memory and approx 1s CPU time on a modern CPU.
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scryptN = 1 << 18 |
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scryptr = 8 |
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@ -99,7 +103,7 @@ func (ks keyStorePassphrase) GenerateNewKey(rand io.Reader, auth string) (key *K |
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return GenerateNewKeyDefault(ks, rand, auth) |
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} |
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func (ks keyStorePassphrase) GetKey(keyAddr []byte, auth string) (key *Key, err error) { |
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func (ks keyStorePassphrase) GetKey(keyAddr common.Address, auth string) (key *Key, err error) { |
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keyBytes, keyId, err := DecryptKey(ks, keyAddr, auth) |
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if err != nil { |
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return nil, err |
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@ -112,43 +116,63 @@ func (ks keyStorePassphrase) GetKey(keyAddr []byte, auth string) (key *Key, err |
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return key, err |
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} |
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func (ks keyStorePassphrase) GetKeyAddresses() (addresses [][]byte, err error) { |
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func (ks keyStorePassphrase) GetKeyAddresses() (addresses []common.Address, err error) { |
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return GetKeyAddresses(ks.keysDirPath) |
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} |
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func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) { |
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authArray := []byte(auth) |
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salt := randentropy.GetEntropyMixed(32) |
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salt := randentropy.GetEntropyCSPRNG(32) |
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derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptr, scryptp, scryptdkLen) |
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if err != nil { |
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return err |
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} |
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encryptKey := Sha3(derivedKey[:16])[:16] |
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keyBytes := FromECDSA(key.PrivateKey) |
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keyBytesHash := Sha3(keyBytes) |
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toEncrypt := PKCS7Pad(append(keyBytes, keyBytesHash...)) |
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toEncrypt := PKCS7Pad(keyBytes) |
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AES256Block, err := aes.NewCipher(derivedKey) |
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AES128Block, err := aes.NewCipher(encryptKey) |
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if err != nil { |
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return err |
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} |
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iv := randentropy.GetEntropyMixed(aes.BlockSize) // 16
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AES256CBCEncrypter := cipher.NewCBCEncrypter(AES256Block, iv) |
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iv := randentropy.GetEntropyCSPRNG(aes.BlockSize) // 16
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AES128CBCEncrypter := cipher.NewCBCEncrypter(AES128Block, iv) |
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cipherText := make([]byte, len(toEncrypt)) |
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AES256CBCEncrypter.CryptBlocks(cipherText, toEncrypt) |
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AES128CBCEncrypter.CryptBlocks(cipherText, toEncrypt) |
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mac := Sha3(derivedKey[16:32], cipherText) |
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cipherStruct := cipherJSON{ |
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salt, |
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iv, |
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cipherText, |
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scryptParamsJSON := scryptParamsJSON{ |
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N: scryptN, |
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R: scryptr, |
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P: scryptp, |
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DkLen: scryptdkLen, |
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Salt: hex.EncodeToString(salt), |
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} |
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keyStruct := encryptedKeyJSON{ |
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key.Id, |
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key.Address, |
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cipherStruct, |
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cipherParamsJSON := cipherparamsJSON{ |
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IV: hex.EncodeToString(iv), |
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} |
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keyJSON, err := json.Marshal(keyStruct) |
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cryptoStruct := cryptoJSON{ |
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Cipher: "aes-128-cbc", |
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CipherText: hex.EncodeToString(cipherText), |
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CipherParams: cipherParamsJSON, |
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KDF: "scrypt", |
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KDFParams: scryptParamsJSON, |
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MAC: hex.EncodeToString(mac), |
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Version: "1", |
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} |
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encryptedKeyJSON := encryptedKeyJSON{ |
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hex.EncodeToString(key.Address[:]), |
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cryptoStruct, |
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key.Id.String(), |
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version, |
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} |
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keyJSON, err := json.Marshal(encryptedKeyJSON) |
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if err != nil { |
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return err |
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} |
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@ -156,18 +180,18 @@ func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) { |
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return WriteKeyFile(key.Address, ks.keysDirPath, keyJSON) |
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} |
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func (ks keyStorePassphrase) DeleteKey(keyAddr []byte, auth string) (err error) { |
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func (ks keyStorePassphrase) DeleteKey(keyAddr common.Address, auth string) (err error) { |
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// only delete if correct passphrase is given
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_, _, err = DecryptKey(ks, keyAddr, auth) |
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if err != nil { |
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return err |
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} |
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keyDirPath := filepath.Join(ks.keysDirPath, hex.EncodeToString(keyAddr)) |
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keyDirPath := filepath.Join(ks.keysDirPath, hex.EncodeToString(keyAddr[:])) |
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return os.RemoveAll(keyDirPath) |
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} |
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func DecryptKey(ks keyStorePassphrase, keyAddr []byte, auth string) (keyBytes []byte, keyId []byte, err error) { |
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func DecryptKey(ks keyStorePassphrase, keyAddr common.Address, auth string) (keyBytes []byte, keyId []byte, err error) { |
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fileContent, err := GetKeyFile(ks.keysDirPath, keyAddr) |
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if err != nil { |
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return nil, nil, err |
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@ -176,25 +200,48 @@ func DecryptKey(ks keyStorePassphrase, keyAddr []byte, auth string) (keyBytes [] |
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keyProtected := new(encryptedKeyJSON) |
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err = json.Unmarshal(fileContent, keyProtected) |
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keyId = keyProtected.Id |
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salt := keyProtected.Crypto.Salt |
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iv := keyProtected.Crypto.IV |
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cipherText := keyProtected.Crypto.CipherText |
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keyId = uuid.Parse(keyProtected.Id) |
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authArray := []byte(auth) |
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derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptr, scryptp, scryptdkLen) |
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mac, err := hex.DecodeString(keyProtected.Crypto.MAC) |
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if err != nil { |
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return nil, nil, err |
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} |
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iv, err := hex.DecodeString(keyProtected.Crypto.CipherParams.IV) |
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if err != nil { |
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return nil, nil, err |
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} |
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cipherText, err := hex.DecodeString(keyProtected.Crypto.CipherText) |
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if err != nil { |
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return nil, nil, err |
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} |
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plainText, err := aesCBCDecrypt(derivedKey, cipherText, iv) |
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salt, err := hex.DecodeString(keyProtected.Crypto.KDFParams.Salt) |
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if err != nil { |
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return nil, nil, err |
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} |
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n := keyProtected.Crypto.KDFParams.N |
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r := keyProtected.Crypto.KDFParams.R |
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p := keyProtected.Crypto.KDFParams.P |
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dkLen := keyProtected.Crypto.KDFParams.DkLen |
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authArray := []byte(auth) |
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derivedKey, err := scrypt.Key(authArray, salt, n, r, p, dkLen) |
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if err != nil { |
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return nil, nil, err |
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} |
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keyBytes = plainText[:len(plainText)-32] |
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keyBytesHash := plainText[len(plainText)-32:] |
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if !bytes.Equal(Sha3(keyBytes), keyBytesHash) { |
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err = errors.New("Decryption failed: checksum mismatch") |
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calculatedMAC := Sha3(derivedKey[16:32], cipherText) |
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if !bytes.Equal(calculatedMAC, mac) { |
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err = errors.New("Decryption failed: MAC mismatch") |
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return nil, nil, err |
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} |
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plainText, err := aesCBCDecrypt(Sha3(derivedKey[:16])[:16], cipherText, iv) |
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if err != nil { |
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return nil, nil, err |
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} |
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return keyBytes, keyId, err |
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return plainText, keyId, err |
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} |
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Jeffrey Wilcke
10 years ago