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pypresent.py
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# Python PRESENT implementation
# Version: 1.0
# Date: 13/10/2008
#
# =============================================================================
# Copyright (c) 2008 Christophe Oosterlynck (christophe.oosterlynck@gmail.com)
# Philippe Teuwen (philippe.teuwen@nxp.com)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
# =============================================================================
""" PRESENT block cipher implementation
USAGE EXAMPLE:
---------------
Importing:
-----------
>>> from pypresent import Present
Encrypting with a 80-bit key:
------------------------------
>>> key = "00000000000000000000".decode('hex')
>>> plain = "0000000000000000".decode('hex')
>>> cipher = Present(key)
>>> encrypted = cipher.encrypt(plain)
>>> encrypted.encode('hex')
'5579c1387b228445'
>>> decrypted = cipher.decrypt(encrypted)
>>> decrypted.encode('hex')
'0000000000000000'
Encrypting with a 128-bit key:
-------------------------------
>>> key = "0123456789abcdef0123456789abcdef".decode('hex')
>>> plain = "0123456789abcdef".decode('hex')
>>> cipher = Present(key)
>>> encrypted = cipher.encrypt(plain)
>>> encrypted.encode('hex')
'0e9d28685e671dd6'
>>> decrypted = cipher.decrypt(encrypted)
>>> decrypted.encode('hex')
'0123456789abcdef'
fully based on standard specifications: http://www.crypto.ruhr-uni-bochum.de/imperia/md/content/texte/publications/conferences/present_ches2007.pdf
test vectors: http://www.crypto.ruhr-uni-bochum.de/imperia/md/content/texte/publications/conferences/slides/present_testvectors.zip
"""
class Present:
def __init__(self,key,rounds=32):
"""Create a PRESENT cipher object
key: the key as a 128-bit or 80-bit rawstring
rounds: the number of rounds as an integer, 32 by default
"""
self.rounds = rounds
if len(key) * 8 == 80:
self.roundkeys = generateRoundkeys80(string2number(key),self.rounds)
elif len(key) * 8 == 128:
self.roundkeys = generateRoundkeys128(string2number(key),self.rounds)
else:
raise ValueError, "Key must be a 128-bit or 80-bit rawstring"
def encrypt(self,block):
"""Encrypt 1 block (8 bytes)
Input: plaintext block as raw string
Output: ciphertext block as raw string
"""
state = string2number(block)
for i in xrange (self.rounds-1):
state = addRoundKey(state,self.roundkeys[i])
state = sBoxLayer(state)
state = pLayer(state)
cipher = addRoundKey(state,self.roundkeys[-1])
return number2string_N(cipher,8)
def decrypt(self,block):
"""Decrypt 1 block (8 bytes)
Input: ciphertext block as raw string
Output: plaintext block as raw string
"""
state = string2number(block)
for i in xrange (self.rounds-1):
state = addRoundKey(state,self.roundkeys[-i-1])
state = pLayer_dec(state)
state = sBoxLayer_dec(state)
decipher = addRoundKey(state,self.roundkeys[0])
return number2string_N(decipher,8)
def get_block_size(self):
return 8
# 0 1 2 3 4 5 6 7 8 9 a b c d e f
Sbox= [0xc,0x5,0x6,0xb,0x9,0x0,0xa,0xd,0x3,0xe,0xf,0x8,0x4,0x7,0x1,0x2]
Sbox_inv = [Sbox.index(x) for x in xrange(16)]
PBox = [0,16,32,48,1,17,33,49,2,18,34,50,3,19,35,51,
4,20,36,52,5,21,37,53,6,22,38,54,7,23,39,55,
8,24,40,56,9,25,41,57,10,26,42,58,11,27,43,59,
12,28,44,60,13,29,45,61,14,30,46,62,15,31,47,63]
PBox_inv = [PBox.index(x) for x in xrange(64)]
def generateRoundkeys80(key,rounds):
"""Generate the roundkeys for a 80-bit key
Input:
key: the key as a 80-bit integer
rounds: the number of rounds as an integer
Output: list of 64-bit roundkeys as integers"""
roundkeys = []
for i in xrange(1,rounds+1): # (K1 ... K32)
# rawkey: used in comments to show what happens at bitlevel
# rawKey[0:64]
roundkeys.append(key >>16)
#1. Shift
#rawKey[19:len(rawKey)]+rawKey[0:19]
key = ((key & (2**19-1)) << 61) + (key >> 19)
#2. SBox
#rawKey[76:80] = S(rawKey[76:80])
key = (Sbox[key >> 76] << 76)+(key & (2**76-1))
#3. Salt
#rawKey[15:20] ^ i
key ^= i << 15
return roundkeys
def generateRoundkeys128(key,rounds):
"""Generate the roundkeys for a 128-bit key
Input:
key: the key as a 128-bit integer
rounds: the number of rounds as an integer
Output: list of 64-bit roundkeys as integers"""
roundkeys = []
for i in xrange(1,rounds+1): # (K1 ... K32)
# rawkey: used in comments to show what happens at bitlevel
roundkeys.append(key >>64)
#1. Shift
key = ((key & (2**67-1)) << 61) + (key >> 67)
#2. SBox
key = (Sbox[key >> 124] << 124)+(Sbox[(key >> 120) & 0xF] << 120)+(key & (2**120-1))
#3. Salt
#rawKey[62:67] ^ i
key ^= i << 62
return roundkeys
def addRoundKey(state,roundkey):
return state ^ roundkey
def sBoxLayer(state):
"""SBox function for encryption
Input: 64-bit integer
Output: 64-bit integer"""
output = 0
for i in xrange(16):
output += Sbox[( state >> (i*4)) & 0xF] << (i*4)
return output
def sBoxLayer_dec(state):
"""Inverse SBox function for decryption
Input: 64-bit integer
Output: 64-bit integer"""
output = 0
for i in xrange(16):
output += Sbox_inv[( state >> (i*4)) & 0xF] << (i*4)
return output
def pLayer(state):
"""Permutation layer for encryption
Input: 64-bit integer
Output: 64-bit integer"""
output = 0
for i in xrange(64):
output += ((state >> i) & 0x01) << PBox[i]
return output
def pLayer_dec(state):
"""Permutation layer for decryption
Input: 64-bit integer
Output: 64-bit integer"""
output = 0
for i in xrange(64):
output += ((state >> i) & 0x01) << PBox_inv[i]
return output
def string2number(i):
""" Convert a string to a number
Input: string (big-endian)
Output: long or integer
"""
return int(i.encode('hex'),16)
def number2string_N(i, N):
"""Convert a number to a string of fixed size
i: long or integer
N: length of string
Output: string (big-endian)
"""
s = '%0*x' % (N*2, i)
return s.decode('hex')
def _test():
import doctest
doctest.testmod()
if __name__ == "__main__":
_test()