/*
This file is part of go-ethereum
go-ethereum is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
go-ethereum is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @authors
* Gustav Simonsson <gustav.simonsson@gmail.com>
* @date 2015
*
*/
/*
This key store behaves as KeyStorePlain with the difference that
the private key is encrypted and on disk uses another JSON encoding.
Cryptography:
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'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, 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].
References:
1. http://www.tarsnap.com/scrypt/scrypt-slides.pdf
2. http://stackoverflow.com/questions/11126315/what-are-optimal-scrypt-work-factors
3. http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
4. http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher-block_chaining_.28CBC.29
5. https://leanpub.com/gocrypto/read#leanpub-auto-block-cipher-modes
6. http://tools.ietf.org/html/rfc2315
7. http://bitcoin.stackexchange.com/questions/3059/what-is-a-compressed-bitcoin-key
8. http://golang.org/pkg/crypto/ecdsa/#PrivateKey
9. https://golang.org/pkg/math/big/#Int.Bytes
*/
package crypto
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"encoding/json"
"errors"
"io"
"os"
"path/filepath"
"code.google.com/p/go-uuid/uuid"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/crypto/randentropy"
"golang.org/x/crypto/scrypt"
)
const (
// 2^18 / 8 / 1 uses 256MB memory and approx 1s CPU time on a modern CPU.
scryptN = 1 << 18
scryptr = 8
scryptp = 1
scryptdkLen = 32
)
type keyStorePassphrase struct {
keysDirPath string
}
func NewKeyStorePassphrase(path string) KeyStore2 {
return &keyStorePassphrase{path}
}
func (ks keyStorePassphrase) GenerateNewKey(rand io.Reader, auth string) (key *Key, err error) {
return GenerateNewKeyDefault(ks, rand, auth)
}
func (ks keyStorePassphrase) GetKey(keyAddr common.Address, auth string) (key *Key, err error) {
keyBytes, keyId, err := DecryptKey(ks, keyAddr, auth)
if err != nil {
return nil, err
}
key = &Key{
Id: uuid.UUID(keyId),
Address: keyAddr,
PrivateKey: ToECDSA(keyBytes),
}
return key, err
}
func (ks keyStorePassphrase) GetKeyAddresses() (addresses []common.Address, err error) {
return GetKeyAddresses(ks.keysDirPath)
}
func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) {
authArray := []byte(auth)
salt := randentropy.GetEntropyCSPRNG(32)
derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptr, scryptp, scryptdkLen)
if err != nil {
return err
}
encryptKey := Sha3(derivedKey[:16])[:16]
keyBytes := FromECDSA(key.PrivateKey)
toEncrypt := PKCS7Pad(keyBytes)
AES128Block, err := aes.NewCipher(encryptKey)
if err != nil {
return err
}
iv := randentropy.GetEntropyCSPRNG(aes.BlockSize) // 16
AES128CBCEncrypter := cipher.NewCBCEncrypter(AES128Block, iv)
cipherText := make([]byte, len(toEncrypt))
AES128CBCEncrypter.CryptBlocks(cipherText, toEncrypt)
mac := Sha3(derivedKey[16:32], cipherText)
cipherStruct := cipherJSON{
mac,
salt,
iv,
cipherText,
}
keyStruct := encryptedKeyJSON{
key.Id,
key.Address.Bytes(),
cipherStruct,
}
keyJSON, err := json.Marshal(keyStruct)
if err != nil {
return err
}
return WriteKeyFile(key.Address, ks.keysDirPath, keyJSON)
}
func (ks keyStorePassphrase) DeleteKey(keyAddr common.Address, auth string) (err error) {
// only delete if correct passphrase is given
_, _, err = DecryptKey(ks, keyAddr, auth)
if err != nil {
return err
}
keyDirPath := filepath.Join(ks.keysDirPath, keyAddr.Hex())
return os.RemoveAll(keyDirPath)
}
func DecryptKey(ks keyStorePassphrase, keyAddr common.Address, auth string) (keyBytes []byte, keyId []byte, err error) {
fileContent, err := GetKeyFile(ks.keysDirPath, keyAddr)
if err != nil {
return nil, nil, err
}
keyProtected := new(encryptedKeyJSON)
err = json.Unmarshal(fileContent, keyProtected)
keyId = keyProtected.Id
mac := keyProtected.Crypto.MAC
salt := keyProtected.Crypto.Salt
iv := keyProtected.Crypto.IV
cipherText := keyProtected.Crypto.CipherText
authArray := []byte(auth)
derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptr, scryptp, scryptdkLen)
if err != nil {
return nil, nil, err
}
calculatedMAC := Sha3(derivedKey[16:32], cipherText)
if !bytes.Equal(calculatedMAC, mac) {
err = errors.New("Decryption failed: MAC mismatch")
return nil, nil, err
}
plainText, err := aesCBCDecrypt(Sha3(derivedKey[:16])[:16], cipherText, iv)
if err != nil {
return nil, nil, err
}
return plainText, keyId, err
}
