crypto/custom_encryption

crypto/custom_encryption/custom_encryption.py

@@ -0,0 +1,64 @@
+from random import randint
+import sys
+
+
+def generator(g, x, p):
+    return pow(g, x) % p
+
+
+def encrypt(plaintext, key):
+    cipher = []
+    for char in plaintext:
+        cipher.append(((ord(char) * key*311)))
+    return cipher
+
+
+def is_prime(p):
+    v = 0
+    for i in range(2, p + 1):
+        if p % i == 0:
+            v = v + 1
+    if v > 1:
+        return False
+    else:
+        return True
+
+
+def dynamic_xor_encrypt(plaintext, text_key):
+    cipher_text = ""
+    key_length = len(text_key)
+    for i, char in enumerate(plaintext[::-1]):
+        key_char = text_key[i % key_length]
+        encrypted_char = chr(ord(char) ^ ord(key_char))
+        cipher_text += encrypted_char
+    return cipher_text
+
+
+def test(plain_text, text_key):
+    p = 97
+    g = 31
+    if not is_prime(p) and not is_prime(g):
+        print("Enter prime numbers")
+        return
+    a = randint(p-10, p)
+    b = randint(g-10, g)
+    print(f"a = {a}")
+    print(f"b = {b}")
+    u = generator(g, a, p)
+    v = generator(g, b, p)
+    key = generator(v, a, p)
+    b_key = generator(u, b, p)
+    shared_key = None
+    if key == b_key:
+        shared_key = key
+    else:
+        print("Invalid key")
+        return
+    semi_cipher = dynamic_xor_encrypt(plain_text, text_key)
+    cipher = encrypt(semi_cipher, shared_key)
+    print(f'cipher is: {cipher}')
+
+
+if __name__ == "__main__":
+    message = sys.argv[1]
+    test(message, "trudeau")

crypto/custom_encryption/enc_flag

@@ -0,0 +1,3 @@
+a = 97
+b = 22
+cipher is: [151146, 1158786, 1276344, 1360314, 1427490, 1377108, 1074816, 1074816, 386262, 705348, 0, 1393902, 352674, 83970, 1141992, 0, 369468, 1444284, 16794, 1041228, 403056, 453438, 100764, 100764, 285498, 100764, 436644, 856494, 537408, 822906, 436644, 117558, 201528, 285498]

crypto/custom_encryption/solve.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+
+def generator(g, x, p):
+    return pow(g, x) % p
+
+# xor encryption is symmetric, apart
+# from the reversing part
+def dynamic_xor_decrypt(plaintext, text_key):
+    cipher_text = ""
+    key_length = len(text_key)
+    for i, char in enumerate(plaintext):
+        key_char = text_key[i % key_length]
+        encrypted_char = chr(ord(char) ^ ord(key_char))
+        cipher_text += encrypted_char
+    return ''.join(reversed(cipher_text))
+
+def decrypt(cipher, key):
+    plaintext = ''
+    for char in cipher:
+        plaintext += chr(char // (key * 311))
+    return plaintext
+
+cipher = [151146, 1158786, 1276344, 1360314, 1427490, 1377108, 1074816, 1074816, 386262, 705348, 0, 1393902, 352674, 83970, 1141992, 0, 369468, 1444284, 16794, 1041228, 403056, 453438, 100764, 100764, 285498, 100764, 436644, 856494, 537408, 822906, 436644, 117558, 201528, 285498]
+
+if __name__ == '__main__':
+    p = 97
+    g = 31
+    a = 97
+    b = 22
+    u = generator(g, a, p)
+    v = generator(g, b, p)
+    key = generator(v, a, p)
+    b_key = generator(u, b, p)
+    assert key == b_key
+    decrypted = decrypt(cipher, key)
+    xor_decrypted = dynamic_xor_decrypt(decrypted, 'trudeau')
+    print(xor_decrypted)
+
+