Merge pull request #259 from Gustav-Simonsson/develop

KeyStore (Low level key functionality)

1 files changed, 245 insertions, 0 deletions

diff --git a/crypto/key_store_passphrase.go b/crypto/key_store_passphrase.go
new file mode 100644
index 000000000..e30a0a785
--- /dev/null
+++ b/crypto/key_store_passphrase.go
@@ -0,0 +1,245 @@
+/*
+	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 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.
+7. Plaintext padding is PKCS #7 [5][6]
+
+Encoding:
+
+1. On disk, ciphertext, 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:
+
+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"
+	"code.google.com/p/go-uuid/uuid"
+	"code.google.com/p/go.crypto/scrypt"
+	"crypto/aes"
+	"crypto/cipher"
+	crand "crypto/rand"
+	"encoding/json"
+	"errors"
+	"io"
+	"os"
+	"path"
+)
+
+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(keyId *uuid.UUID, auth string) (key *Key, err error) {
+	keyBytes, err := DecryptKey(ks, keyId, auth)
+	if err != nil {
+		return nil, err
+	}
+	key = &Key{
+		Id:         keyId,
+		PrivateKey: ToECDSA(keyBytes),
+	}
+	return key, err
+}
+
+func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) {
+	authArray := []byte(auth)
+	salt := getEntropyCSPRNG(32)
+	derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptr, scryptp, scryptdkLen)
+	if err != nil {
+		return err
+	}
+
+	keyBytes := FromECDSA(key.PrivateKey)
+	keyBytesHash := Sha3(keyBytes)
+	toEncrypt := PKCS7Pad(append(keyBytes, keyBytesHash...))
+
+	AES256Block, err := aes.NewCipher(derivedKey)
+	if err != nil {
+		return err
+	}
+
+	iv := getEntropyCSPRNG(aes.BlockSize) // 16
+	AES256CBCEncrypter := cipher.NewCBCEncrypter(AES256Block, iv)
+	cipherText := make([]byte, len(toEncrypt))
+	AES256CBCEncrypter.CryptBlocks(cipherText, toEncrypt)
+
+	cipherStruct := cipherJSON{
+		salt,
+		iv,
+		cipherText,
+	}
+	keyStruct := encryptedKeyJSON{
+		*key.Id,
+		cipherStruct,
+	}
+	keyJSON, err := json.Marshal(keyStruct)
+	if err != nil {
+		return err
+	}
+
+	return WriteKeyFile(key.Id.String(), ks.keysDirPath, keyJSON)
+}
+
+func (ks keyStorePassphrase) DeleteKey(keyId *uuid.UUID, auth string) (err error) {
+	// only delete if correct passphrase is given
+	_, err = DecryptKey(ks, keyId, auth)
+	if err != nil {
+		return err
+	}
+
+	keyDirPath := path.Join(ks.keysDirPath, keyId.String())
+	return os.RemoveAll(keyDirPath)
+}
+
+func DecryptKey(ks keyStorePassphrase, keyId *uuid.UUID, auth string) (keyBytes []byte, err error) {
+	fileContent, err := GetKeyFile(ks.keysDirPath, keyId)
+	if err != nil {
+		return nil, err
+	}
+
+	keyProtected := new(encryptedKeyJSON)
+	err = json.Unmarshal(fileContent, keyProtected)
+
+	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, err
+	}
+
+	AES256Block, err := aes.NewCipher(derivedKey)
+	if err != nil {
+		return nil, err
+	}
+
+	AES256CBCDecrypter := cipher.NewCBCDecrypter(AES256Block, iv)
+	paddedPlainText := make([]byte, len(cipherText))
+	AES256CBCDecrypter.CryptBlocks(paddedPlainText, cipherText)
+
+	plainText := PKCS7Unpad(paddedPlainText)
+	if plainText == nil {
+		err = errors.New("Decryption failed: PKCS7Unpad failed after decryption")
+		return 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")
+		return nil, err
+	}
+	return keyBytes, err
+}
+
+func getEntropyCSPRNG(n int) []byte {
+	mainBuff := make([]byte, n)
+	_, err := io.ReadFull(crand.Reader, mainBuff)
+	if err != nil {
+		panic("key generation: reading from crypto/rand failed: " + err.Error())
+	}
+	return mainBuff
+}
+
+// From https://leanpub.com/gocrypto/read#leanpub-auto-block-cipher-modes
+func PKCS7Pad(in []byte) []byte {
+	padding := 16 - (len(in) % 16)
+	if padding == 0 {
+		padding = 16
+	}
+	for i := 0; i < padding; i++ {
+		in = append(in, byte(padding))
+	}
+	return in
+}
+
+func PKCS7Unpad(in []byte) []byte {
+	if len(in) == 0 {
+		return nil
+	}
+
+	padding := in[len(in)-1]
+	if int(padding) > len(in) || padding > aes.BlockSize {
+		return nil
+	} else if padding == 0 {
+		return nil
+	}
+
+	for i := len(in) - 1; i > len(in)-int(padding)-1; i-- {
+		if in[i] != padding {
+			return nil
+		}
+	}
+	return in[:len(in)-int(padding)]
+}