script.py

#This AWS lambda is setup at:
#https://o5lyi532hb.execute-api.us-east-1.amazonaws.com/default/ecboracle?prefixhex=00112233

import json
import os
import sys
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad


def lambda_handler(event, context):
    prefix=bytes.fromhex(event["queryStringParameters"]["prefixhex"])
    flag = os.environ["flag"]
    padded = pad(prefix + flag.encode(), 16)
    cipher = AES.new(os.environ["secretkey"].encode(), AES.MODE_ECB)
    try:
        encrypted = cipher.encrypt(padded)
    except ValueError as e:
        return {'statusCode': 500, "error": str(e)}

    return {
        'statusCode': 200,
        'body': json.dumps({"ciphertext": encrypted.hex()})
    }