utilities for XOR/ROT substritution cipher

gistfile1.txt

$ python
Python 2.7.3 (default, Feb 27 2014, 20:00:17)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from xortools import *
>>> plaintext = 'This program cannot be run in DOS mode.'
>>> ciphertext = xorencode(plaintext, 'AX')
>>> ciphertext
'\x150(+a(37&* 5a; 6/75x#=a*46a1/x\x05\x17\x12x,7%=o'
>>> find_xorkey(ciphertext, 'program', keylen=2)
'AX': 'This program cannot be run in DOS mode.'
>>> xordecode(ciphertext, 'AX')
'This program cannot be run in DOS mode.'
>>> ciphertext = rotencode(plaintext, 8)
>>> ciphertext
'Bpqa xzwoziu kivvwb jm zcv qv LWA uwlm.'
>>> find_rotkey(ciphertext)
0: 'Bpqa xzwoziu kivvwb jm zcv qv LWA uwlm.'
1: 'Aopz wyvnyht jhuuva il ybu pu KVZ tvkl.'
2: 'Znoy vxumxgs igttuz hk xat ot JUY sujk.'
3: 'Ymnx uwtlwfr hfssty gj wzs ns ITX rtij.'
4: 'Xlmw tvskveq gerrsx fi vyr mr HSW qshi.'
5: 'Wklv surjudp fdqqrw eh uxq lq GRV prgh.'
6: 'Vjku rtqitco ecppqv dg twp kp FQU oqfg.'
7: 'Uijt qsphsbn dboopu cf svo jo EPT npef.'
8: 'This program cannot be run in DOS mode.'
9: 'Sghr oqnfqzl bzmmns ad qtm hm CNR lncd.'
10: 'Rfgq npmepyk ayllmr zc psl gl BMQ kmbc.'
11: 'Qefp moldoxj zxkklq yb ork fk ALP jlab.'
12: 'Pdeo lnkcnwi ywjjkp xa nqj ej ZKO ikza.'
13: 'Ocdn kmjbmvh xviijo wz mpi di YJN hjyz.'
14: 'Nbcm jlialug wuhhin vy loh ch XIM gixy.'
15: 'Mabl ikhzktf vtgghm ux kng bg WHL fhwx.'
16: 'Lzak hjgyjse usffgl tw jmf af VGK egvw.'
17: 'Kyzj gifxird treefk sv ile ze UFJ dfuv.'
18: 'Jxyi fhewhqc sqddej ru hkd yd TEI cetu.'
19: 'Iwxh egdvgpb rpccdi qt gjc xc SDH bdst.'
20: 'Hvwg dfcufoa qobbch ps fib wb RCG acrs.'
21: 'Guvf cebtenz pnaabg or eha va QBF zbqr.'
22: 'Ftue bdasdmy omzzaf nq dgz uz PAE yapq.'
23: 'Estd aczrclx nlyyze mp cfy ty OZD xzop.'
24: 'Drsc zbyqbkw mkxxyd lo bex sx NYC wyno.'
25: 'Cqrb yaxpajv ljwwxc kn adw rw MXB vxmn.'
>>> rotdecode(ciphertext, 8)
'This program cannot be run in DOS mode.'
>>>

xortools.py

from itertools import cycle, product

def xorencode(s, key='\xFF'):
    return ''.join(chr(ord(x)^ord(y)) for x, y in zip(s, cycle(key)))

xordecode = xorencode

def find_xorkey(s, word, keylen=1):
    for tup in product(xrange(0x100), repeat=keylen):
        key = ''.join(chr(x) for x in tup)
        s2 = xordecode(s, key)
        if word in s2:
            print "%r: %r" % (key, s2)

def rotencode(s, n=13):
    a = []
    for c in s:
        x = ord(c) - 0x41
        if 0 <= x < 0x1B:
            a.append(chr(0x41 + ((x+n) % 26)))
            continue
        x -= 0x20
        if 0 <= x < 0x1B:
            a.append(chr(0x61 + ((x+n) % 26)))
            continue
        a.append(c)
    return ''.join(a)

def rotdecode(s, n=13):
    return rotencode(s, 26-n)

def find_rotkey(s):
    for i in xrange(26):
        x = rotdecode(s, i)
        print "%d: %r" % (i, x)