funga-eth/funga/eth/keystore/keyfile.py

# standard imports
import os
import hashlib
import logging
import json
import uuid

# external imports
import coincurve
from Crypto.Cipher import AES
from Crypto.Util import Counter
import sha3

# local imports
from funga.error import (
        DecryptError,
        KeyfileError,
        )
from funga.eth.encoding import private_key_to_address

logg = logging.getLogger(__name__)

algo_keywords = [
    'aes-128-ctr',
        ]
hash_keywords = [
    'scrypt'
        ]

default_kdfparams = {
    'dklen': 32,
    'n': 1 << 18,
    'p': 1,
    'r': 8,
    'salt': os.urandom(32).hex(),
        }


def to_mac(mac_key, ciphertext_bytes):
    h = sha3.keccak_256()
    h.update(mac_key)
    h.update(ciphertext_bytes)
    return h.digest()


class Hashes:

    @staticmethod
    def from_scrypt(kdfparams=default_kdfparams, passphrase=''):
        dklen = int(kdfparams['dklen']) 
        n = int(kdfparams['n']) 
        p = int(kdfparams['p']) 
        r = int(kdfparams['r']) 
        salt = bytes.fromhex(kdfparams['salt'])

        return hashlib.scrypt(passphrase.encode('utf-8'), salt=salt,n=n, p=p, r=r, maxmem=1024*1024*1024, dklen=dklen)

    
class Ciphers:

    aes_128_block_size = 1 << 7
    aes_iv_len = 16

    @staticmethod
    def decrypt_aes_128_ctr(ciphertext, decryption_key, iv):
        ctr = Counter.new(Ciphers.aes_128_block_size, initial_value=iv)
        cipher = AES.new(decryption_key, AES.MODE_CTR, counter=ctr)
        plaintext = cipher.decrypt(ciphertext)
        return plaintext


    @staticmethod
    def encrypt_aes_128_ctr(plaintext, encryption_key, iv):
        ctr = Counter.new(Ciphers.aes_128_block_size, initial_value=iv)
        cipher = AES.new(encryption_key, AES.MODE_CTR, counter=ctr)
        ciphertext = cipher.encrypt(plaintext)
        return ciphertext


def to_dict(private_key_bytes, passphrase=''):
   
    private_key = coincurve.PrivateKey(secret=private_key_bytes)

    encryption_key = Hashes.from_scrypt(passphrase=passphrase)

    address_hex = private_key_to_address(private_key)
    iv_bytes = os.urandom(Ciphers.aes_iv_len)
    iv = int.from_bytes(iv_bytes, 'big')
    ciphertext_bytes = Ciphers.encrypt_aes_128_ctr(private_key.secret, encryption_key[:16], iv)

    mac = to_mac(encryption_key[16:], ciphertext_bytes)

    crypto_dict = {
        'cipher': 'aes-128-ctr',
        'ciphertext': ciphertext_bytes.hex(),
        'cipherparams': {
            'iv': iv_bytes.hex(),
            },
        'kdf': 'scrypt',
        'kdfparams': default_kdfparams,
        'mac': mac.hex(),
        }

    uu = uuid.uuid1()
    o = {
        'address': address_hex,
        'version': 3,
        'crypto': crypto_dict,
        'id': str(uu),
        }
    return o


def from_dict(o, passphrase=''):

    cipher = o['crypto']['cipher']
    if cipher not in algo_keywords:
        raise NotImplementedError('cipher "{}" not implemented'.format(cipher))

    kdf = o['crypto']['kdf']
    if kdf not in hash_keywords:
        raise NotImplementedError('kdf "{}" not implemented'.format(kdf))

    m = getattr(Hashes, 'from_{}'.format(kdf.replace('-', '_'))) 
    decryption_key = m(o['crypto']['kdfparams'], passphrase)

    control_mac = bytes.fromhex(o['crypto']['mac'])
    iv_bytes = bytes.fromhex(o['crypto']['cipherparams']['iv'])
    iv = int.from_bytes(iv_bytes, "big")
    ciphertext_bytes = bytes.fromhex(o['crypto']['ciphertext'])
    
    # check mac
    calculated_mac = to_mac(decryption_key[16:], ciphertext_bytes)
    if control_mac != calculated_mac:
        raise DecryptError('mac mismatch when decrypting passphrase')
    
    m = getattr(Ciphers, 'decrypt_{}'.format(cipher.replace('-', '_')))

    try:
        pk = m(ciphertext_bytes, decryption_key[:16], iv)
    except AssertionError as e:
        raise DecryptError('could not decrypt keyfile: {}'.format(e))

    return pk


def from_file(filepath, passphrase=''):

    f = open(filepath, 'r')
    try:
        o = json.load(f)
    except json.decoder.JSONDecodeError as e:
        f.close()
        raise KeyfileError(e)
    f.close()

    return from_dict(o, passphrase)


def from_some(v, passphrase=''):
    if isinstance(v, bytes):
        v = v.decode('utf-8')

    if isinstance(v, str):
        try:
            return from_file(v, passphrase)
        except Exception:
            logg.debug('keyfile parse as file fail')
            pass
        v = json.loads(v)

    return from_dict(v, passphrase)