aes.py

"""
A pure python (slow) implementation of rijndael with a decent interface

To include -

from rijndael import rijndael

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
"""

# ported from the Java reference code by Bram Cohen, bram@gawth.com, April 2001
# 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

import copy
import string



#-----------------------
#TREV - ADDED BECAUSE THERE'S WARNINGS ABOUT INT OVERFLOW BEHAVIOR CHANGING IN
#2.4.....
import os
if os.name != "java":
    import exceptions
    if hasattr(exceptions, "FutureWarning"):
        import warnings
        warnings.filterwarnings("ignore", category=FutureWarning, append=1)
#-----------------------



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]]]

# [keysize][block_size]
num_rounds = {16: {16: 10, 24: 12, 32: 14}, 24: {16: 12, 24: 12, 32: 14}, 32: {16: 14, 24: 14, 32: 14}}

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]

# S-boxes and inverse S-boxes
S =  [0] * 256
Si = [0] * 256
for i in xrange(256):
    S[i] = cox[i][0] << 7
    for t in xrange(1, 8):
        S[i] ^= cox[i][t] << (7-t)
    Si[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

T1 = []
T2 = []
T3 = []
T4 = []
T5 = []
T6 = []
T7 = []
T8 = []
U1 = []
U2 = []
U3 = []
U4 = []

for t in xrange(256):
    s = S[t]
    T1.append(mul4(s, G[0]))
    T2.append(mul4(s, G[1]))
    T3.append(mul4(s, G[2]))
    T4.append(mul4(s, G[3]))

    s = Si[t]
    T5.append(mul4(s, iG[0]))
    T6.append(mul4(s, iG[1]))
    T7.append(mul4(s, iG[2]))
    T8.append(mul4(s, iG[3]))

    U1.append(mul4(t, iG[0]))
    U2.append(mul4(t, iG[1]))
    U3.append(mul4(t, iG[2]))
    U4.append(mul4(t, iG[3]))

# round constants
rcon = [1]
r = 1
for t in xrange(1, 30):
    r = mul(2, r)
    rcon.append(r)

del A
del AA
del pivot
del B
del G
del box
del log
del alog
del i
del j
del r
del s
del t
del mul
del mul4
del cox
del iG

class rijndael:
    def __init__(self, key, block_size = 16):
        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 = 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] ^= (S[(tt >> 16) & 0xFF] & 0xFF) << 24 ^  \
                     (S[(tt >>  8) & 0xFF] & 0xFF) << 16 ^  \
                     (S[ tt        & 0xFF] & 0xFF) <<  8 ^  \
                     (S[(tt >> 24) & 0xFF] & 0xFF)       ^  \
                     (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] ^= (S[ tt        & 0xFF] & 0xFF)       ^ \
                              (S[(tt >>  8) & 0xFF] & 0xFF) <<  8 ^ \
                              (S[(tt >> 16) & 0xFF] & 0xFF) << 16 ^ \
                              (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] = U1[(tt >> 24) & 0xFF] ^ \
                           U2[(tt >> 16) & 0xFF] ^ \
                           U3[(tt >>  8) & 0xFF] ^ \
                           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:
            SC = 0
        elif BC == 6:
            SC = 1
        else:
            SC = 2
        s1 = shifts[SC][1][0]
        s2 = shifts[SC][2][0]
        s3 = shifts[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] = (T1[(t[ i           ] >> 24) & 0xFF] ^
                        T2[(t[(i + s1) % BC] >> 16) & 0xFF] ^
                        T3[(t[(i + s2) % BC] >>  8) & 0xFF] ^
                        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((S[(t[ i           ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
            result.append((S[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
            result.append((S[(t[(i + s2) % BC] >>  8) & 0xFF] ^ (tt >>  8)) & 0xFF)
            result.append((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(plaintext)))
        Kd = self.Kd

        BC = self.block_size / 4
        ROUNDS = len(Kd) - 1
        if BC == 4:
            SC = 0
        elif BC == 6:
            SC = 1
        else:
            SC = 2
        s1 = shifts[SC][1][1]
        s2 = shifts[SC][2][1]
        s3 = shifts[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] = (T5[(t[ i           ] >> 24) & 0xFF] ^
                        T6[(t[(i + s1) % BC] >> 16) & 0xFF] ^
                        T7[(t[(i + s2) % BC] >>  8) & 0xFF] ^
                        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((Si[(t[ i           ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
            result.append((Si[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
            result.append((Si[(t[(i + s2) % BC] >>  8) & 0xFF] ^ (tt >>  8)) & 0xFF)
            result.append((Si[ t[(i + s3) % BC]        & 0xFF] ^  tt       ) & 0xFF)
        return string.join(map(chr, result), '')

def encrypt(key, block):
    return rijndael(key, len(block)).encrypt(block)

def decrypt(key, block):
    return rijndael(key, len(block)).decrypt(block)

def test():
    def t(kl, bl):
        b = 'b' * bl
        r = rijndael('a' * kl, bl)
        assert r.decrypt(r.encrypt(b)) == 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)