Skip to content

Instantly share code, notes, and snippets.

@jeetsukumaran

jeetsukumaran/rijndael.py

Created October 17, 2011 02:54
Show Gist options
  • Star 23 You must be signed in to star a gist
  • Fork 7 You must be signed in to fork a gist
  • Save jeetsukumaran/1291836 to your computer and use it in GitHub Desktop.
Save jeetsukumaran/1291836 to your computer and use it in GitHub Desktop.
Download ZIP
Pure-Python implementation of Rijndael (AES) cipher.
Raw
rijndael.py
#############################################################################
# Original code ported from the Java reference code by Bram Cohen, April 2001,
# with the following statement:
#
# this code is public domain, unless someone makes
# an intellectual property claim against the reference
# code, in which case it can be made public domain by
# deleting all the comments and renaming all the variables
#
class Rijndael(object):
"""
A pure python (slow) implementation of rijndael with a decent interface.
To do a key setup::
r = Rijndael(key, block_size = 16)
key must be a string of length 16, 24, or 32
blocksize must be 16, 24, or 32. Default is 16
To use::
ciphertext = r.encrypt(plaintext)
plaintext = r.decrypt(ciphertext)
If any strings are of the wrong length a ValueError is thrown
"""
@classmethod
def create(cls):
if hasattr(cls, "RIJNDAEL_CREATED"):
return
# [keysize][block_size]
cls.num_rounds = {16: {16: 10, 24: 12, 32: 14}, 24: {16: 12, 24: 12, 32: 14}, 32: {16: 14, 24: 14, 32: 14}}
cls.shifts = [[[0, 0], [1, 3], [2, 2], [3, 1]],
[[0, 0], [1, 5], [2, 4], [3, 3]],
[[0, 0], [1, 7], [3, 5], [4, 4]]]
A = [[1, 1, 1, 1, 1, 0, 0, 0],
[0, 1, 1, 1, 1, 1, 0, 0],
[0, 0, 1, 1, 1, 1, 1, 0],
[0, 0, 0, 1, 1, 1, 1, 1],
[1, 0, 0, 0, 1, 1, 1, 1],
[1, 1, 0, 0, 0, 1, 1, 1],
[1, 1, 1, 0, 0, 0, 1, 1],
[1, 1, 1, 1, 0, 0, 0, 1]]
# produce log and alog tables, needed for multiplying in the
# field GF(2^m) (generator = 3)
alog = [1]
for i in xrange(255):
j = (alog[-1] << 1) ^ alog[-1]
if j & 0x100 != 0:
j ^= 0x11B
alog.append(j)
log = [0] * 256
for i in xrange(1, 255):
log[alog[i]] = i
# multiply two elements of GF(2^m)
def mul(a, b):
if a == 0 or b == 0:
return 0
return alog[(log[a & 0xFF] + log[b & 0xFF]) % 255]
# substitution box based on F^{-1}(x)
box = [[0] * 8 for i in xrange(256)]
box[1][7] = 1
for i in xrange(2, 256):
j = alog[255 - log[i]]
for t in xrange(8):
box[i][t] = (j >> (7 - t)) & 0x01
B = [0, 1, 1, 0, 0, 0, 1, 1]
# affine transform: box[i] <- B + A*box[i]
cox = [[0] * 8 for i in xrange(256)]
for i in xrange(256):
for t in xrange(8):
cox[i][t] = B[t]
for j in xrange(8):
cox[i][t] ^= A[t][j] * box[i][j]
# cls.S-boxes and inverse cls.S-boxes
cls.S = [0] * 256
cls.Si = [0] * 256
for i in xrange(256):
cls.S[i] = cox[i][0] << 7
for t in xrange(1, 8):
cls.S[i] ^= cox[i][t] << (7-t)
cls.Si[cls.S[i] & 0xFF] = i
# T-boxes
G = [[2, 1, 1, 3],
[3, 2, 1, 1],
[1, 3, 2, 1],
[1, 1, 3, 2]]
AA = [[0] * 8 for i in xrange(4)]
for i in xrange(4):
for j in xrange(4):
AA[i][j] = G[i][j]
AA[i][i+4] = 1
for i in xrange(4):
pivot = AA[i][i]
if pivot == 0:
t = i + 1
while AA[t][i] == 0 and t < 4:
t += 1
assert t != 4, 'G matrix must be invertible'
for j in xrange(8):
AA[i][j], AA[t][j] = AA[t][j], AA[i][j]
pivot = AA[i][i]
for j in xrange(8):
if AA[i][j] != 0:
AA[i][j] = alog[(255 + log[AA[i][j] & 0xFF] - log[pivot & 0xFF]) % 255]
for t in xrange(4):
if i != t:
for j in xrange(i+1, 8):
AA[t][j] ^= mul(AA[i][j], AA[t][i])
AA[t][i] = 0
iG = [[0] * 4 for i in xrange(4)]
for i in xrange(4):
for j in xrange(4):
iG[i][j] = AA[i][j + 4]
def mul4(a, bs):
if a == 0:
return 0
r = 0
for b in bs:
r <<= 8
if b != 0:
r = r | mul(a, b)
return r
cls.T1 = []
cls.T2 = []
cls.T3 = []
cls.T4 = []
cls.T5 = []
cls.T6 = []
cls.T7 = []
cls.T8 = []
cls.U1 = []
cls.U2 = []
cls.U3 = []
cls.U4 = []
for t in xrange(256):
s = cls.S[t]
cls.T1.append(mul4(s, G[0]))
cls.T2.append(mul4(s, G[1]))
cls.T3.append(mul4(s, G[2]))
cls.T4.append(mul4(s, G[3]))
s = cls.Si[t]
cls.T5.append(mul4(s, iG[0]))
cls.T6.append(mul4(s, iG[1]))
cls.T7.append(mul4(s, iG[2]))
cls.T8.append(mul4(s, iG[3]))
cls.U1.append(mul4(t, iG[0]))
cls.U2.append(mul4(t, iG[1]))
cls.U3.append(mul4(t, iG[2]))
cls.U4.append(mul4(t, iG[3]))
# round constants
cls.rcon = [1]
r = 1
for t in xrange(1, 30):
r = mul(2, r)
cls.rcon.append(r)
cls.RIJNDAEL_CREATED = True
def __init__(self, key, block_size = 16):
# create common meta-instance infrastructure
self.create()
if block_size != 16 and block_size != 24 and block_size != 32:
raise ValueError('Invalid block size: ' + str(block_size))
if len(key) != 16 and len(key) != 24 and len(key) != 32:
raise ValueError('Invalid key size: ' + str(len(key)))
self.block_size = block_size
ROUNDS = Rijndael.num_rounds[len(key)][block_size]
BC = block_size / 4
# encryption round keys
Ke = [[0] * BC for i in xrange(ROUNDS + 1)]
# decryption round keys
Kd = [[0] * BC for i in xrange(ROUNDS + 1)]
ROUND_KEY_COUNT = (ROUNDS + 1) * BC
KC = len(key) / 4
# copy user material bytes into temporary ints
tk = []
for i in xrange(0, KC):
tk.append((ord(key[i * 4]) << 24) | (ord(key[i * 4 + 1]) << 16) |
(ord(key[i * 4 + 2]) << 8) | ord(key[i * 4 + 3]))
# copy values into round key arrays
t = 0
j = 0
while j < KC and t < ROUND_KEY_COUNT:
Ke[t / BC][t % BC] = tk[j]
Kd[ROUNDS - (t / BC)][t % BC] = tk[j]
j += 1
t += 1
tt = 0
rconpointer = 0
while t < ROUND_KEY_COUNT:
# extrapolate using phi (the round key evolution function)
tt = tk[KC - 1]
tk[0] ^= (Rijndael.S[(tt >> 16) & 0xFF] & 0xFF) << 24 ^ \
(Rijndael.S[(tt >> 8) & 0xFF] & 0xFF) << 16 ^ \
(Rijndael.S[ tt & 0xFF] & 0xFF) << 8 ^ \
(Rijndael.S[(tt >> 24) & 0xFF] & 0xFF) ^ \
(Rijndael.rcon[rconpointer] & 0xFF) << 24
rconpointer += 1
if KC != 8:
for i in xrange(1, KC):
tk[i] ^= tk[i-1]
else:
for i in xrange(1, KC / 2):
tk[i] ^= tk[i-1]
tt = tk[KC / 2 - 1]
tk[KC / 2] ^= (Rijndael.S[ tt & 0xFF] & 0xFF) ^ \
(Rijndael.S[(tt >> 8) & 0xFF] & 0xFF) << 8 ^ \
(Rijndael.S[(tt >> 16) & 0xFF] & 0xFF) << 16 ^ \
(Rijndael.S[(tt >> 24) & 0xFF] & 0xFF) << 24
for i in xrange(KC / 2 + 1, KC):
tk[i] ^= tk[i-1]
# copy values into round key arrays
j = 0
while j < KC and t < ROUND_KEY_COUNT:
Ke[t / BC][t % BC] = tk[j]
Kd[ROUNDS - (t / BC)][t % BC] = tk[j]
j += 1
t += 1
# inverse MixColumn where needed
for r in xrange(1, ROUNDS):
for j in xrange(BC):
tt = Kd[r][j]
Kd[r][j] = Rijndael.U1[(tt >> 24) & 0xFF] ^ \
Rijndael.U2[(tt >> 16) & 0xFF] ^ \
Rijndael.U3[(tt >> 8) & 0xFF] ^ \
Rijndael.U4[ tt & 0xFF]
self.Ke = Ke
self.Kd = Kd
def encrypt(self, plaintext):
if len(plaintext) != self.block_size:
raise ValueError('wrong block length, expected ' + str(self.block_size) + ' got ' + str(len(plaintext)))
Ke = self.Ke
BC = self.block_size / 4
ROUNDS = len(Ke) - 1
if BC == 4:
Rijndael.SC = 0
elif BC == 6:
Rijndael.SC = 1
else:
Rijndael.SC = 2
s1 = Rijndael.shifts[Rijndael.SC][1][0]
s2 = Rijndael.shifts[Rijndael.SC][2][0]
s3 = Rijndael.shifts[Rijndael.SC][3][0]
a = [0] * BC
# temporary work array
t = []
# plaintext to ints + key
for i in xrange(BC):
t.append((ord(plaintext[i * 4 ]) << 24 |
ord(plaintext[i * 4 + 1]) << 16 |
ord(plaintext[i * 4 + 2]) << 8 |
ord(plaintext[i * 4 + 3]) ) ^ Ke[0][i])
# apply round transforms
for r in xrange(1, ROUNDS):
for i in xrange(BC):
a[i] = (Rijndael.T1[(t[ i ] >> 24) & 0xFF] ^
Rijndael.T2[(t[(i + s1) % BC] >> 16) & 0xFF] ^
Rijndael.T3[(t[(i + s2) % BC] >> 8) & 0xFF] ^
Rijndael.T4[ t[(i + s3) % BC] & 0xFF] ) ^ Ke[r][i]
t = copy.copy(a)
# last round is special
result = []
for i in xrange(BC):
tt = Ke[ROUNDS][i]
result.append((Rijndael.S[(t[ i ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
result.append((Rijndael.S[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
result.append((Rijndael.S[(t[(i + s2) % BC] >> 8) & 0xFF] ^ (tt >> 8)) & 0xFF)
result.append((Rijndael.S[ t[(i + s3) % BC] & 0xFF] ^ tt ) & 0xFF)
return string.join(map(chr, result), '')
def decrypt(self, ciphertext):
if len(ciphertext) != self.block_size:
raise ValueError('wrong block length, expected ' + str(self.block_size) + ' got ' + str(len(ciphertext)))
Kd = self.Kd
BC = self.block_size / 4
ROUNDS = len(Kd) - 1
if BC == 4:
Rijndael.SC = 0
elif BC == 6:
Rijndael.SC = 1
else:
Rijndael.SC = 2
s1 = Rijndael.shifts[Rijndael.SC][1][1]
s2 = Rijndael.shifts[Rijndael.SC][2][1]
s3 = Rijndael.shifts[Rijndael.SC][3][1]
a = [0] * BC
# temporary work array
t = [0] * BC
# ciphertext to ints + key
for i in xrange(BC):
t[i] = (ord(ciphertext[i * 4 ]) << 24 |
ord(ciphertext[i * 4 + 1]) << 16 |
ord(ciphertext[i * 4 + 2]) << 8 |
ord(ciphertext[i * 4 + 3]) ) ^ Kd[0][i]
# apply round transforms
for r in xrange(1, ROUNDS):
for i in xrange(BC):
a[i] = (Rijndael.T5[(t[ i ] >> 24) & 0xFF] ^
Rijndael.T6[(t[(i + s1) % BC] >> 16) & 0xFF] ^
Rijndael.T7[(t[(i + s2) % BC] >> 8) & 0xFF] ^
Rijndael.T8[ t[(i + s3) % BC] & 0xFF] ) ^ Kd[r][i]
t = copy.copy(a)
# last round is special
result = []
for i in xrange(BC):
tt = Kd[ROUNDS][i]
result.append((Rijndael.Si[(t[ i ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
result.append((Rijndael.Si[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
result.append((Rijndael.Si[(t[(i + s2) % BC] >> 8) & 0xFF] ^ (tt >> 8)) & 0xFF)
result.append((Rijndael.Si[ t[(i + s3) % BC] & 0xFF] ^ tt ) & 0xFF)
return string.join(map(chr, result), '')
# @staticmethod
# def encrypt_block(key, block):
# return Rijndael(key, len(block)).encrypt(block)
# @staticmethod
# def decrypt_block(key, block):
# return Rijndael(key, len(block)).decrypt(block)
@staticmethod
def test():
def t(kl, bl):
b = 'b' * bl
r = Rijndael('a' * kl, bl)
x = r.encrypt(b)
assert x != b
assert r.decrypt(x) == b
t(16, 16)
t(16, 24)
t(16, 32)
t(24, 16)
t(24, 24)
t(24, 32)
t(32, 16)
t(32, 24)
t(32, 32)
# Rijndael
#############################################################################
@MichaelK866
Copy link

How can I use the code to encrypt a Windows or Linux partition? e.g. F:/ or sda4 ?

@AnirudhKonduru
Copy link

How can I use the code to encrypt a Windows or Linux partition? e.g. F:/ or sda4 ?

@MichaelK866 Please don't. This was probably written as an exercise to understand the algorithm. To encrypt/decrypt your stuff, use more standardized, battle tested tools(like LUKS for linux).

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment