shared.py

import os
import hashlib
import nacl.secret
import nacl.utils

def get_flag_env():
    flag = os.getenv('GZCTF_FLAG')
    if flag is None:
        flag = 'GZT{this_is_a_test_flag}'
    return flag

def get_key():
    seed = hashlib.sha512(get_flag_env().encode()).digest()
    key_size = nacl.secret.SecretBox.KEY_SIZE
    nonce_size = nacl.secret.SecretBox.NONCE_SIZE
    key = seed[:key_size]
    nonce = seed[key_size:key_size+nonce_size]
    return key, nonce

def enc_red_packet(red_packet):
    key, nonce = get_key()
    box = nacl.secret.SecretBox(key)
    return box.encrypt(red_packet.encode(), nonce).ciphertext.hex()

def dec_red_packet(enc_red_packet):
    key, nonce = get_key()
    box = nacl.secret.SecretBox(key)
    return box.decrypt(bytes.fromhex(enc_red_packet), nonce).decode()

if __name__ == '__main__':
    print("key seed :", get_flag_env())
    enc = enc_red_packet('这是一个测试红包')
    print("encrypt  :", enc)
    dec = dec_red_packet(enc)
    print("decrypt  :", dec)