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196 lines (155 loc) · 5.59 KB
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"""
Pure Python implementation of SEAL3
Reference:
https://link.springer.com/article/10.1007/s001459900048
"""
from __future__ import annotations
import struct
from typing import Iterable
from refinery.lib.crypto import rotr32
from refinery.units.crypto.cipher import StreamCipherUnit
__all__ = ['seal']
class SEAL_Gamma:
"""
This class implements the key derivation for the SEAL cipher.
"""
def _process(self, state, w):
"""
This is a pure Python implementation of a SHA1 Round.
"""
def lrot(b, n):
return ((n << b) | (n >> (32 - b))) & 0xFFFFFFFF
for t in range(16, 80):
w.append(lrot(1, w[t - 3] ^ w[t - 8] ^ w[t - 14] ^ w[t - 16]))
a, b, c, d, e = state
for t in range(80):
if t < 20:
k = 0x5A827999
f = d ^ (b & (c ^ d))
elif t < 40:
k = 0x6ED9EBA1
f = b ^ c ^ d
elif t < 60:
k = 0x8F1BBCDC
f = (b & c) | (b & d) | (c & d)
else:
k = 0xCA62C1D6
f = b ^ c ^ d
e = (lrot(5, a) + f + e + w[t] + k) & 0xFFFFFFFF
a, b, c, d, e = e, a, lrot(30, b), c, d
return (
(state[0] + a) & 0xFFFFFFFF,
(state[1] + b) & 0xFFFFFFFF,
(state[2] + c) & 0xFFFFFFFF,
(state[3] + d) & 0xFFFFFFFF,
(state[4] + e) & 0xFFFFFFFF
)
def process(self, w):
self.state = self._process(self.state, w)
def apply(self, i):
sha_index = i // 5
if sha_index != self.last_index:
self.D[0] = sha_index
self.state = tuple(self.H)
self.process(list(self.D))
self.last_index = sha_index
return self.state[i % 5]
def __init__(self, key, byteswap=True):
self.last_index = 0xFFFFFFFF
self.D = 0x10 * [0]
prefix = '>' if byteswap else '<'
self.H = struct.unpack(prefix + 'IIIII', key)
class SEAL_Cipher:
"""
Implementation of the SEAL algorithm. The `byteswap` option can be set
to false if the key already has the correct byte order to be used as a
SHA1 state.
"""
def __init__(self, key, byteswap=True):
self.gamma = SEAL_Gamma(key, byteswap)
self.counter_inside = 0
self.counter_outside = 0
self.counter_start = 0
self.iterations_per_count = 4
self.T = B''.join(
struct.pack('<I', self.gamma.apply(i)) for i in range(512))
self.S = [self.gamma.apply(i + 1 * 0x1000) for i in range(256)]
self.R = [self.gamma.apply(i + 2 * 0x1000) for i in range(16)]
def ttab(self, index):
value, = struct.unpack('<I', self.T[index:index + 4])
return value
def __iter__(self):
def rotr9(n):
return 0xFFFFFFFF & (((n & 0xFFFFFFF) >> 9) | (n << 23))
while True:
a = ( self.counter_outside) ^ self.R[4 * self.counter_inside + 0] # noqa
b = rotr32(0x08, self.counter_outside) ^ self.R[4 * self.counter_inside + 1] # noqa
c = rotr32(0x10, self.counter_outside) ^ self.R[4 * self.counter_inside + 2] # noqa
d = rotr32(0x18, self.counter_outside) ^ self.R[4 * self.counter_inside + 3] # noqa
def warp():
nonlocal a, b, c, d
p = a & 0x7FC; b += self.ttab(p); a = rotr9(a) # noqa
p = b & 0x7FC; c += self.ttab(p); b = rotr9(b) # noqa
p = c & 0x7FC; d += self.ttab(p); c = rotr9(c) # noqa
p = d & 0x7FC; a += self.ttab(p); d = rotr9(d) # noqa
warp()
warp()
w, x, y, z = d, b, a, c
warp()
a, b, c, d = a, b, c, d
for i in range(64):
p = a & 0x7FC
a = rotr9(a)
b += self.ttab(p)
b ^= a
q = b & 0x7FC
b = rotr9(b)
c ^= self.ttab(q)
c += b
p = (p + c) & 0x7FC
c = rotr9(c)
d += self.ttab(p)
d ^= c
q = (q + d) & 0x7FC
d = rotr9(d)
a ^= self.ttab(q)
a += d
p = (p + a) & 0x7FC
b ^= self.ttab(p)
a = rotr9(a)
q = (q + b) & 0x7FC
c += self.ttab(q)
b = rotr9(b)
p = (p + c) & 0x7FC
d ^= self.ttab(p)
c = rotr9(c)
q = (q + d) & 0x7FC
d = rotr9(d)
a += self.ttab(q)
a &= 0xFFFFFFFF
b &= 0xFFFFFFFF
c &= 0xFFFFFFFF
d &= 0xFFFFFFFF
yield from bytearray(struct.pack('<IIII',
(b + self.S[4 * i + 0]) & 0xFFFFFFFF, c ^ self.S[4 * i + 1],
(d + self.S[4 * i + 2]) & 0xFFFFFFFF, a ^ self.S[4 * i + 3]))
if i & 1:
a += y
b += z
c ^= y
d ^= z
else:
a += w
b += x
c ^= w
d ^= x
self.counter_inside = (self.counter_inside + 1) % self.iterations_per_count
if not self.counter_inside:
self.counter_outside += 1
class seal(StreamCipherUnit):
"""
SEAL encryption and decryption.
"""
key_size = {20}
def keystream(self) -> Iterable[bytes]:
return SEAL_Cipher(self.args.key)