CTFs and solutions

guess-mode-double-shot/attack.py

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+#!/usr/bin/env python3
+
+from pwn import *
+
+HOST = "130.192.5.212"
+PORT = "6532"
+
+server = remote(HOST, PORT)
+sleepT = 0.5
+# Different IV when CBC therefore different encryption?
+for i in range(128):
+    print('-'*20)
+    print(server.recv(1024))
+    payload = (b'A'*32).hex()
+    server.send(payload)
+    server.send('\n')
+    sleep(sleepT)
+    enc = server.recv(1024).split(b":")[1].split(b'\n')[0].strip()
+    print(f"Encryption1:{enc}")
+    enc = bytes.fromhex(enc.decode('utf-8'))
+    sleep(sleepT)
+    #payload2 =  bytes([d1 ^ e1 for d1, e1 in zip(b'A'*32, enc)])
+    payload2 = (b'A'*32).hex()
+    #print(payload2)
+
+    #payload2= (b'B'*32).hex()
+    server.send(payload2)
+    server.send('\n')
+    sleep(sleepT)
+    enc2 = server.recv(1024).split(b":")[1].split(b'\n')[0].strip()
+    #print(enc)
+    print(f"Encryption2:{enc2}")
+    enc2 = bytes.fromhex(enc2.decode('utf-8'))
+    sleep(sleepT)
+    if(enc==enc2):
+        print("ECB")
+        server.send(b"ECB")
+        server.send("\n")
+    else:
+        print("CBC")
+        server.send(b"CBC")
+        server.send("\n")
+        sleep(sleepT)
+    #print(server.recv(1024))
+    sleep(sleepT)
+
+print(server.recv(1024))

guess-mode-double-shot/chall.py

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+from Cryptodome.Cipher import AES
+from Cryptodome.Random import get_random_bytes
+#from secret import flag
+import random
+flag="puppa"
+modes_mapping = {
+    "ECB": AES.MODE_ECB,
+    "CBC": AES.MODE_CBC
+}
+
+
+class RandomCipherRandomMode():
+    def __init__(self):
+        modes = [AES.MODE_ECB, AES.MODE_CBC]
+        self.mode = random.choice(modes)
+        self.key = get_random_bytes(32)
+        if self.mode == AES.MODE_ECB:
+            self.iv = None
+            self.cipher = AES.new(key=self.key, mode=self.mode)
+        else:
+            self.iv = get_random_bytes(16)
+            self.cipher = AES.new(key=self.key, iv=self.iv, mode=self.mode)
+
+    def encrypt(self, data):
+        return self.cipher.encrypt(data)
+
+    def decrypt(self, data):
+        return self.cipher.decrypt(data)
+
+
+def main():
+
+    for i in range(128):
+        cipher = RandomCipherRandomMode()
+
+        print(f"Challenge #{i}")
+
+        data = b"\00"*32
+
+        otp = get_random_bytes(len(data))
+        #I dont know the OTP generated
+        for _ in range(2):
+            print(f"The otp is:{otp.hex()}")
+            #data = bytes.fromhex(input("Input: ").strip())
+            if len(data) != 32:
+                print("Data must be 32 bytes long")
+                return
+            data = bytes([d ^ o for d, o in zip(data, otp)])
+            print(f"Output: {cipher.encrypt(data).hex()}")
+        mode_test = input(f"What mode did I use? (ECB, CBC)\n")
+        if mode_test in modes_mapping.keys() and modes_mapping[mode_test] == cipher.mode:
+            print("OK, next")
+        else:
+            print("Wrong, sorry")
+            return
+
+    print(f"The flag is: {flag}")
+
+
+if __name__ == "__main__":
+    main()