From a1c2749380523178f87ae3fdfb02bc6641362924 Mon Sep 17 00:00:00 2001 From: Gustav Simonsson Date: Wed, 7 Jan 2015 16:06:26 +0100 Subject: Address pull request comments MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit * 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 Enterprise™ * Change test error logging to use t.Error(err) * Reduce number of naked returns (just like my ex-gf) * Simplify file reading path code --- crypto/key_store_passphrase.go | 253 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 253 insertions(+) create mode 100644 crypto/key_store_passphrase.go (limited to 'crypto/key_store_passphrase.go') diff --git a/crypto/key_store_passphrase.go b/crypto/key_store_passphrase.go new file mode 100644 index 000000000..eaf73422f --- /dev/null +++ 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 . +*/ +/** + * @authors + * Gustav Simonsson + * @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)] +} -- cgit v1.2.3