common/encrypt_template.py

#!/usr/bin/env python3
"""
Encrypt a plaintext using the protocol's cipher.

Usage: python encrypt.py <plaintext_hex> [--key-hex KEY] [--iv-hex IV]

Input:  plaintext as a hexadecimal string
Output: ciphertext as a hexadecimal string on stdout

This script applies ONLY the cipher layer -- no compression,
base64, or transport encoding.
"""
import sys


def encrypt(plaintext: bytes, key: bytes | None = None, iv: bytes | None = None) -> bytes:
    """Encrypt plaintext bytes and return ciphertext bytes.

    Implement the cipher used by this protocol.
    Do not apply compression, base64, or transport encoding.
    """
    raise NotImplementedError("TODO: implement encryption")


def main():
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <plaintext_hex> [--key-hex KEY] [--iv-hex IV]",
              file=sys.stderr)
        sys.exit(1)

    plaintext = bytes.fromhex(sys.argv[1])

    key_hex = None
    iv_hex = None
    i = 2
    while i < len(sys.argv):
        if sys.argv[i] == "--key-hex" and i + 1 < len(sys.argv):
            key_hex = sys.argv[i + 1]
            i += 2
        elif sys.argv[i] == "--iv-hex" and i + 1 < len(sys.argv):
            iv_hex = sys.argv[i + 1]
            i += 2
        else:
            i += 1

    key = bytes.fromhex(key_hex) if key_hex else None
    iv = bytes.fromhex(iv_hex) if iv_hex else None

    ciphertext = encrypt(plaintext, key, iv)
    print(ciphertext.hex())


if __name__ == "__main__":
    main()