implement aes cbc, block size needs to be fixed

TPs/TP02/py/cfich_aes_cbc.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+import os
+import argparse
+
+def setup(key_file):
+    f = open(key_file,"wb")
+    key_bytes = os.urandom(32)
+    f.write(key_bytes)
+    f.close()
+
+def encrypt(input_file, key_file):
+    fkey = open(key_file,"rb")
+    inp = open(input_file,"rb")
+    out = open(f"{input_file}.enc","wb")
+
+    key = fkey.read()
+    plaintext = inp.read()
+    print(f"plaintext len : {len(plaintext)}")
+    iv = os.urandom(16)
+    # FIX: block size for aes must be 16 bytes
+    # plaintext needs padding
+    cipher = Cipher(algorithms.AES(key),modes.CBC(iv))
+    encryptor = cipher.encryptor()
+    ciphertext = encryptor.update(plaintext)
+    print(f"plaintext len : {len(plaintext)}")
+    print(f"ciphertext len : {len(ciphertext)}")
+    print(f"iv len : {len(iv)}")
+    ciphertext = iv + ciphertext
+
+    out.write(ciphertext)
+
+    fkey.close()
+    inp.close()
+    out.close()
+
+def decrypt(input_file,key_file):
+    fkey = open(key_file,"rb")
+    inp = open(f"{input_file}","rb")
+    out = open(f"{input_file}.dec","wb")
+
+    key = fkey.read()
+    input_bytes = inp.read()
+    iv = input_bytes[:16]
+    ciphertext = input_bytes[16:]
+
+    # FIX: block size for aes must be 16 bytes
+    # plaintext needs padding
+    cipher = Cipher(algorithms.AES(key=key),mode=modes.CBC(iv))
+    decryptor = cipher.decryptor()
+    plaintext = decryptor.update(ciphertext)
+
+    out.write(plaintext)
+
+    fkey.close()
+    inp.close()
+    out.close()
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Program to perform operations using AES cipher on files",
+    )
+
+    subparsers = parser.add_subparsers(dest="operation", help="Operation to perform")
+
+    # Setup subcommand
+    setup_parser = subparsers.add_parser("setup", help="Setup a key file")
+    setup_parser.add_argument("fkey", help="File to contain the appropriate key for the AES cipher")
+
+    # Encrypt subcommand
+    enc_parser = subparsers.add_parser("enc", help="Encrypt a file")
+    enc_parser.add_argument("fich", help="File to be encrypted")
+    enc_parser.add_argument("fkey", help="File containing the key for the AES cipher")
+
+    # Decrypt subcommand
+    dec_parser = subparsers.add_parser("dec", help="Decrypt a file")
+    dec_parser.add_argument("fich", help="File to be decrypted")
+    dec_parser.add_argument("fkey", help="File containing the key for the AES cipher")
+
+    args = parser.parse_args()
+    match args.operation:
+        case "setup":
+            key_file = args.fkey
+            setup(key_file)
+        case "enc":
+            input_file = args.fich
+            key_file = args.fkey
+            encrypt(input_file,key_file)
+        case "dec":
+            input_file = args.fich
+            key_file = args.fkey
+            decrypt(input_file,key_file)
+
+if __name__ == "__main__":
+    main()