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set1/challenge6.py

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+from Crypto.Util.number import *
+import base64
+import statistics
+
+def hamming_distance(str1: str, str2: str) -> int:
+    if len(str1) != len(str2):
+        raise ValueError("Input strings must have the same length")
+
+    hamming = bin(bytes_to_long(str1) ^ bytes_to_long(str2))
+    distance = 0
+    for one in hamming:
+        if one == '1':
+            distance = distance + 1
+
+    return distance
+
+
+# a = b'this is a test'
+# b = b'wokka wokka!!!'
+# print(hamming_distance(a,b))
+
+with open("set1/6.txt",'r') as file:
+    lines = file.readlines()
+base64_str = "".join(line.strip() for line in lines)
+cipher = base64.b64decode(base64_str)
+
+# variances = [99]
+# for key_size in range(2,40):
+#     # print('key_size',key_size)
+#     a = hamming_distance(cipher[0: key_size], cipher[key_size:2 * key_size]) / key_size
+#     b = hamming_distance(cipher[2 * key_size: 3 * key_size], cipher[3 * key_size: 4 * key_size]) / key_size
+#     c = hamming_distance(cipher[4 * key_size: 5 * key_size], cipher[5 * key_size: 6 * key_size]) / key_size
+#     d = hamming_distance(cipher[6 * key_size: 7 * key_size], cipher[7 * key_size: 8 * key_size]) / key_size
+#     data = [a, b, c, d]
+#     variances.append(statistics.variance(data))
+    
+# print(variances.index(min(variances)))
+
+for keysz in range(2, 40):
+    print(keysz, hamming_distance(cipher[:keysz], cipher[keysz: 2 * keysz]) * 1.0 / keysz, sum([hamming_distance(cipher[keysz * i:keysz * i + keysz], cipher[: keysz]) for i in range(10)]) * 1.0 / keysz)
+
+
+
+
+# key_size = 4
+# for key_size in range(1,40):
+    # print(len(cipher) / key_size)
+# for i in range(int(len(cipher) / key_size)):
+#     for key in range(255):
+#         decrypted = "".join(chr(b ^ key) for b in cipher[i * key_size: i * key_size + key_size])
+#         print(decrypted)
+