timelock.py

import scrypt
import sys
from itertools import count
from nacl.secret import SecretBox
from nacl.utils import random
from nacl.exceptions import CryptoError

def kdf(password):
    N = 16384
    r = 1024
    p = 1
    return scrypt.hash(password, 'timelock', N, r, p, SecretBox.KEY_SIZE)

if sys.argv[1] == 'e':
    minutes = int(float(sys.argv[2]) * 8.0)
    key = sys.argv[3]
    for i in xrange(minutes):
        key = kdf(key)
    nonce = random(SecretBox.NONCE_SIZE)
    message = sys.argv[4]
    box = SecretBox(key)
    encrypted = box.encrypt(message, nonce)
    print encrypted.encode('base64').replace('\n', '')
elif sys.argv[1] == 'd':
    key = sys.argv[2]
    ciphertext = sys.argv[3].decode('base64')
    for i in count():
        key = kdf(key)
        print 'trying', i
        box = SecretBox(key)
        try:
            print box.decrypt(ciphertext)
            break
        except CryptoError, e:
            pass