commit ec1908d607e1536e792fdc710cca740a5cfbb21a
parent 469d63f8a0571fe80dc545235dd8e11b955dfa4a
Author: mpizzzle <michael.770211@gmail.com>
Date: Sun, 5 Nov 2017 21:39:36 +0000
set 3 challenge 19/20 pretty much complete (I get the gist)
Diffstat:
3 files changed, 123 insertions(+), 3 deletions(-)
diff --git a/set3/break_fixed_nonce_ctr_statistically.py b/set3/break_fixed_nonce_ctr_statistically.py
@@ -0,0 +1,42 @@
+from Crypto.Cipher import AES
+from Crypto import Random
+from Crypto.Util import Counter
+
+frequent_letters = "etaoishr ETAOISHR"
+key = Random.new().read(AES.block_size)
+
+def encrypt(plaintext):
+ return AES.new(key, AES.MODE_CTR, counter=Counter.new(128)).encrypt(plaintext)
+
+def get_candidate_key_byte(transposed_block):
+ candidate = ''
+ candidate_frequency = 0
+
+ for c in range(256):
+ plaintext = ''.join([chr(c ^ ord(a)) for a in transposed_block])
+ frequency = sum([plaintext.count(frequent_letters[n]) for n in range(len(frequent_letters))])
+
+ if frequency > candidate_frequency:
+ candidate = chr(c)
+ candidate_frequency = frequency
+
+ return candidate
+
+def decrypt(key, msg):
+ return ''.join([chr(ord(key[i % len(key)]) ^ ord(char)) for i, char in enumerate(msg)])
+
+def get_key(file, key_length):
+ split_file = [file[i:i + key_length] for i in range(0, len(file), key_length)]
+ transposed_blocks = [''.join([block[x] for block in split_file[:len(split_file) - 1]]) for x in range(key_length)]
+ return ''.join([get_candidate_key_byte(block) for block in transposed_blocks])
+
+with open('files/20.txt') as f:
+ ciphertexts = [encrypt(line.decode("base64")) for line in f.read().splitlines()]
+
+key_length = min(len(ct) for ct in ciphertexts)
+ciphertext = ''.join([ct[:key_length] for ct in ciphertexts])
+found_key = get_key(ciphertext, key_length)
+plaintext = decrypt(found_key, ciphertext)
+
+for line in [plaintext[i:i + key_length] for i in range(0, len(plaintext), key_length)]:
+ print line
diff --git a/set3/break_fixed_nonce_ctr_using_substitutions.py b/set3/break_fixed_nonce_ctr_using_substitutions.py
@@ -4,8 +4,26 @@ from Crypto.Util import Counter
key = Random.new().read(AES.block_size)
+def encrypt(plaintext):
+ return AES.new(key, AES.MODE_CTR, counter=Counter.new(128)).encrypt(plaintext)
+
+def xor(a, b):
+ return "".join([chr(ord(x) ^ ord(y)) for (x, y) in zip(a, b)])
+
with open('files/19.txt') as f:
- ciphertexts = [AES.new(key, AES.MODE_CTR, counter=Counter.new(64,initial_value=0,little_endian=True,prefix="\x00\x00\x00\x00\x00\x00\x00\x00")).encrypt(line) for line in f.read().splitlines()]
+ ciphertexts = [encrypt(line.decode("base64")) for line in f.read().splitlines()]
+
+def drag_crib(crib, a_xor_b):
+ derp = []
+ for n in range(len(a_xor_b) - len(crib) + 1):
+ potential = xor(crib, a_xor_b[n : n + len(crib)])
+
+ #if all(x.isalpha() or x.isspace() for x in potential):
+ # if crib not in potential:
+ derp.append(potential)
+ print derp
-for ct in ciphertexts:
- print ct
+for i in range(40):
+ if i != 5:
+ print i
+ drag_crib("r polite ", xor(ciphertexts[i], ciphertexts[5]))
diff --git a/set3/files/20.txt b/set3/files/20.txt
@@ -0,0 +1,60 @@
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