def __init__(self, seed=None):
if not seed:
seed = urandom(56)
elif len(seed) < 4 * 8 + 3 * 8:
raise Exception('Seed value too short')
self.key_words = [
littleendian2int(seed[i * 4:i * 4 + 4]) for i in range(8)
]
self.nonce_words = [
littleendian2int(seed[32 + i * 4:32 + i * 4 + 4]) for _ in range(3)
]
self.counter = 1
self.buf = ""
def chacha20_decrypt(data, key, counter=1):
"Decrypt a string using a key"
key = fixed_length_key(key, 32)
key_words = [littleendian2int(key[i:i + 4]) for i in range(0, 32, 4)]
nonce_words = [littleendian2int(data[i:i + 4]) for i in range(0, 12, 4)]
ciphertext = data[12:]
plaintext = ""
for i in range(0, len(ciphertext), 64):
j = _i32(i // 64)
key_stream = chacha20_block(key_words, [_i32(counter + j)],
nonce_words)
block = ciphertext[i:i + 64]
plaintext += xor_str(block, key_stream)
return plaintext
def chacha20_encrypt(plaintext, key, counter=1):
"Encrypt a string using a key"
key = fixed_length_key(key, 32)
key_words = [littleendian2int(key[i:i + 4]) for i in range(0, 32, 4)]
nonce_words = [littleendian2int(urandom(4)) for _ in range(3)]
ciphertext = "".join([int2littleendian(n, 4) for n in nonce_words])
for i in range(0, len(plaintext), 64):
j = _i32(i // 64)
key_stream = chacha20_block(key_words, [_i32(counter + j)],
nonce_words)
block = plaintext[i:i + 64]
ciphertext += xor_str(block, key_stream)
return ciphertext
def poly1305(data, key):
"Poly1305 message authentication code"
r = littleendian2int(key[:16])
r = clamp(r)
s = littleendian2int(key[16:])
accumulator = 0
p = (1 << 130) - 5
for i in range(0, len(data), 16):
block = data[i:i + 16]
n = littleendian2int(block)
onebit = 2**(len(block) * 8)
n = n + onebit
accumulator += n
accumulator = (r * accumulator) % p
accumulator += s
tag = int2littleendian(accumulator, 16)[:16]
return tag
def poly1305_key_gen(key, nonce):
counter = 0
key_words = [littleendian2int(key[i:i + 4]) for i in range(0, 32, 4)]
nonce_words = [littleendian2int(nonce[i:i + 4]) for i in range(0, 12, 4)]
block = crypturd.chacha20_block(key_words, [counter], nonce_words)
return block[:32]