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authorGustav Simonsson <gustav.simonsson@gmail.com>2015-01-07 23:06:26 +0800
committerGustav Simonsson <gustav.simonsson@gmail.com>2015-01-16 02:40:10 +0800
commita1c2749380523178f87ae3fdfb02bc6641362924 (patch)
tree4e8a22b27b6f219f311531a52a87589be1e40520 /crypto/key_store_passphrase.go
parent945798f913d5cabd79635f45045b680b02396bf9 (diff)
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Address pull request comments
* Simplify scrypt constants with const block * Add key store constructors and make their types private * Simplify key store and file namings to be less Java Enterpriseā„¢ * Change test error logging to use t.Error(err) * Reduce number of naked returns (just like my ex-gf) * Simplify file reading path code
Diffstat (limited to 'crypto/key_store_passphrase.go')
-rw-r--r--crypto/key_store_passphrase.go253
1 files changed, 253 insertions, 0 deletions
diff --git a/crypto/key_store_passphrase.go b/crypto/key_store_passphrase.go
new file mode 100644
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+++ b/crypto/key_store_passphrase.go
@@ -0,0 +1,253 @@
+/*
+ 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 KeyStorePlaintextFile with the difference that
+the private key is encrypted and encoded as a JSON object within the
+key JSON object.
+
+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 as a JSON object.
+ cat a key file to see the structure.
+2. byte arrays are ASCII HEX encoded as 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"
+ "encoding/hex"
+ "encoding/json"
+ "errors"
+ "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 {
+ ks := new(keyStorePassphrase)
+ ks.keysDirPath = path
+ return ks
+}
+
+func (ks keyStorePassphrase) GenerateNewKey(auth string) (key *Key, err error) {
+ return GenerateNewKeyDefault(ks, auth)
+}
+
+func (ks keyStorePassphrase) GetKey(keyId *uuid.UUID, auth string) (key *Key, err error) {
+ keyBytes, flags, err := DecryptKey(ks, keyId, auth)
+ if err != nil {
+ return nil, err
+ }
+ key = new(Key)
+ key.Id = keyId
+ copy(key.Flags[:], flags[0:4])
+ key.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{
+ hex.EncodeToString(salt),
+ hex.EncodeToString(iv),
+ hex.EncodeToString(cipherText),
+ }
+ keyStruct := EncryptedKeyJSON{
+ key.Id.String(),
+ hex.EncodeToString(key.Flags[:]),
+ 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, flags []byte, err error) {
+ fileContent, err := GetKeyFile(ks.keysDirPath, keyId)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ keyProtected := new(EncryptedKeyJSON)
+ err = json.Unmarshal(fileContent, keyProtected)
+
+ flags, err = hex.DecodeString(keyProtected.Flags)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ salt, err := hex.DecodeString(keyProtected.Crypto.Salt)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ iv, err := hex.DecodeString(keyProtected.Crypto.IV)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ cipherText, err := hex.DecodeString(keyProtected.Crypto.CipherText)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ authArray := []byte(auth)
+ derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptr, scryptp, scryptdkLen)
+ if err != nil {
+ return nil, nil, err
+ }
+
+ AES256Block, err := aes.NewCipher(derivedKey)
+ if err != nil {
+ return nil, 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, 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, nil, err
+ }
+ return keyBytes, flags, err
+}
+
+// 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)]
+}