246 lines
6.5 KiB
Go
246 lines
6.5 KiB
Go
/*
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This file is part of go-ethereum
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go-ethereum is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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go-ethereum is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @authors
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* Gustav Simonsson <gustav.simonsson@gmail.com>
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* @date 2015
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*
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*/
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/*
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This key store behaves as KeyStorePlain with the difference that
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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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(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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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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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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1. http://www.tarsnap.com/scrypt/scrypt-slides.pdf
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2. http://stackoverflow.com/questions/11126315/what-are-optimal-scrypt-work-factors
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3. http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
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4. http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher-block_chaining_.28CBC.29
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5. https://leanpub.com/gocrypto/read#leanpub-auto-block-cipher-modes
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6. http://tools.ietf.org/html/rfc2315
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7. http://bitcoin.stackexchange.com/questions/3059/what-is-a-compressed-bitcoin-key
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8. http://golang.org/pkg/crypto/ecdsa/#PrivateKey
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9. https://golang.org/pkg/math/big/#Int.Bytes
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*/
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package crypto
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import (
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"bytes"
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"code.google.com/p/go-uuid/uuid"
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"code.google.com/p/go.crypto/scrypt"
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"crypto/aes"
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"crypto/cipher"
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crand "crypto/rand"
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"encoding/json"
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"errors"
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"io"
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"os"
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"path"
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)
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const (
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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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scryptp = 1
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scryptdkLen = 32
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)
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type keyStorePassphrase struct {
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keysDirPath string
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}
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func NewKeyStorePassphrase(path string) KeyStore2 {
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return &keyStorePassphrase{path}
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}
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func (ks keyStorePassphrase) GenerateNewKey(rand io.Reader, auth string) (key *Key, err error) {
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return GenerateNewKeyDefault(ks, rand, auth)
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}
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func (ks keyStorePassphrase) GetKey(keyId *uuid.UUID, auth string) (key *Key, err error) {
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keyBytes, err := DecryptKey(ks, keyId, auth)
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if err != nil {
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return nil, err
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}
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key = &Key{
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Id: keyId,
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PrivateKey: ToECDSA(keyBytes),
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}
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return key, err
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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 := 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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keyBytes := FromECDSA(key.PrivateKey)
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keyBytesHash := Sha3(keyBytes)
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toEncrypt := PKCS7Pad(append(keyBytes, keyBytesHash...))
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AES256Block, err := aes.NewCipher(derivedKey)
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if err != nil {
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return err
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}
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iv := getEntropyCSPRNG(aes.BlockSize) // 16
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AES256CBCEncrypter := cipher.NewCBCEncrypter(AES256Block, iv)
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cipherText := make([]byte, len(toEncrypt))
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AES256CBCEncrypter.CryptBlocks(cipherText, toEncrypt)
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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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}
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keyStruct := encryptedKeyJSON{
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*key.Id,
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cipherStruct,
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}
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keyJSON, err := json.Marshal(keyStruct)
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if err != nil {
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return err
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}
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return WriteKeyFile(key.Id.String(), ks.keysDirPath, keyJSON)
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}
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func (ks keyStorePassphrase) DeleteKey(keyId *uuid.UUID, auth string) (err error) {
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// only delete if correct passphrase is given
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_, err = DecryptKey(ks, keyId, auth)
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if err != nil {
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return err
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}
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keyDirPath := path.Join(ks.keysDirPath, keyId.String())
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return os.RemoveAll(keyDirPath)
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}
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func DecryptKey(ks keyStorePassphrase, keyId *uuid.UUID, auth string) (keyBytes []byte, err error) {
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fileContent, err := GetKeyFile(ks.keysDirPath, keyId)
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if err != nil {
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return nil, err
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}
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keyProtected := new(encryptedKeyJSON)
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err = json.Unmarshal(fileContent, keyProtected)
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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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authArray := []byte(auth)
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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 nil, err
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}
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AES256Block, err := aes.NewCipher(derivedKey)
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if err != nil {
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return nil, err
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}
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AES256CBCDecrypter := cipher.NewCBCDecrypter(AES256Block, iv)
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paddedPlainText := make([]byte, len(cipherText))
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AES256CBCDecrypter.CryptBlocks(paddedPlainText, cipherText)
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plainText := PKCS7Unpad(paddedPlainText)
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if plainText == nil {
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err = errors.New("Decryption failed: PKCS7Unpad failed after decryption")
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return 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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return nil, err
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}
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return keyBytes, err
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}
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func getEntropyCSPRNG(n int) []byte {
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mainBuff := make([]byte, n)
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_, err := io.ReadFull(crand.Reader, mainBuff)
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if err != nil {
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panic("key generation: reading from crypto/rand failed: " + err.Error())
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}
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return mainBuff
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}
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// From https://leanpub.com/gocrypto/read#leanpub-auto-block-cipher-modes
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func PKCS7Pad(in []byte) []byte {
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padding := 16 - (len(in) % 16)
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if padding == 0 {
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padding = 16
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}
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for i := 0; i < padding; i++ {
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in = append(in, byte(padding))
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}
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return in
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}
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func PKCS7Unpad(in []byte) []byte {
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if len(in) == 0 {
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return nil
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}
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padding := in[len(in)-1]
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if int(padding) > len(in) || padding > aes.BlockSize {
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return nil
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} else if padding == 0 {
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return nil
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}
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for i := len(in) - 1; i > len(in)-int(padding)-1; i-- {
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if in[i] != padding {
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return nil
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}
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}
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return in[:len(in)-int(padding)]
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}
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