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@kravietz

kravietz/break.py

Created Nov 7, 2017
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Vigenere over bytes (XOR) statistical solver
#!/usr/bin/env python3
import collections
import statistics
line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
ciphertext = []
for i in range(0, len(line)-2, 2):
b = line[i] + line[i+1]
ciphertext.append(int(b, 16))
def hex_print(c):
for i in c:
print("{:02X} ".format(i), end="")
print()
def ischar(c):
return (c >= 32 and c <= 47) or (c >= 57 and c < 127)
qis = []
for hkl in range(2, 10):
# hkl - hypothetical key length
# take each hkl-th character and form a string hcr - hypothetical cryptogram
hcr = ciphertext[::hkl]
#print('*** Trying key length', hkl)
#hex_print(hcr)
counter = collections.Counter(hcr)
q = [x/len(hcr) for x in counter.values()]
#print('q=', q)
q2 = [x**2 for x in q]
#print('q2=', q2)
q3 = sum(q2)
#print('q3=', q3, 'N=', hkl)
if q3 > 0.065:
print('*** Found key length N=', hkl)
N = hkl
keystream = []
print('*** Trying to break key bytes')
english = 'etaoinshrdlcumwfgypbvkjxqz'
def distance(s1, s2):
s2 = s2[:len(s1)]
return sum(abs(ord(x) - ord(y)) for x,y in zip(s1, s2))
import difflib
for i in range(N):
stream = ciphertext[i::N]
print('stream=', end='')
hex_print(stream)
candidates = {}
for k in range(256):
fail = False
stream_p = []
for c in stream:
p = c ^ k
# even one non-alpha char means this key byte is wrong
if not ischar(p):
fail = True
#print('x')
break
# append decrypted char to stream plaintext
p = chr(p).lower()
if p >= 'a' and p <= 'z':
stream_p.append(p)
if not fail:
print('stream_p=', ''.join(stream_p))
# test 1/2 all decrypted chars must be alpha
if not fail:
# test 2/2 letter frequency matches English
print('*** Trying key byte i={} k={:02x}'.format(i, k))
c = collections.Counter(stream_p)
# because c.most_common() is a dictionary and dictionary hashes in Python
# are randomized, the exact sequence returned here will be *different on each run*
freq = ''.join(x[0] for x in c.most_common())
ratio = difflib.SequenceMatcher(a=freq, b=english).ratio()
print('freq=', freq, 'ratio=', ratio)
candidates[k] = ratio
keystream.append(max(candidates, key=candidates.get))
print('Keystream')
hex_print(keystream)
i = 0
plaintext = []
for c in ciphertext:
p = c ^ keystream[i % len(keystream)]
i += 1
plaintext.append(chr(p))
for c in plaintext:
print(c, end='')
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