Authenticated Chacha20 in python

TPs/TP03/py/pbenc_chacha20_poly1305.py

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+from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
+import argparse
+import os
+
+
+def setup(key_file):
+    key = ChaCha20Poly1305.generate_key()
+    with open(key_file, "wb") as f:
+        f.write(key)
+
+
+def encrypt(input_file, key_file):
+    with open(key_file, "rb") as f:
+        key = f.read(32)
+
+    with open(input_file, "rb") as f:
+        plaintext = f.read()
+
+    aad = b"authenticated but unencrypted data"
+    nonce = os.urandom(12)
+
+    cipher = ChaCha20Poly1305(key)
+    ciphertext = cipher.encrypt(nonce, plaintext, aad)
+
+    with open(f"{input_file}.enc", "wb") as f:
+        f.write(nonce + ciphertext)
+
+
+
+def decrypt(input_file, key_file):
+    with open(key_file, "rb") as f:
+        key = f.read(32)
+    
+    with open(input_file, "rb") as f:
+        input_bytes = f.read()
+
+    aad = b"authenticated but unencrypted data"
+    nonce = input_bytes[:12]
+    ciphertext = input_bytes[12:]
+
+
+    cipher = ChaCha20Poly1305(key)
+    plaintext = cipher.decrypt(nonce, ciphertext, aad)
+
+    with open(f"{input_file}.dec", "wb") as f:
+        f.write(plaintext)
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Program to perform operations using Authenticated ChaCha20 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 ChaCha20 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 ChaCha20 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 ChaCha20 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)
+        case "help":
+            parser.print_help()
+
+if __name__ == "__main__":
+    main()