crypt.py

import numpy as np
import time

from utils import polyadd, polymul
from keygen import gen_normal_poly, gen_binary_poly


def encrypt(pk, size, q, t, poly_mod, pt):
    """Encrypt an integer.
    Args:
        pk: public-key.
        size: size of polynomials.
        q: ciphertext modulus.
        t: plaintext modulus.
        poly_mod: polynomial modulus.
        pt: integer to be encrypted.
    Returns:
        Tuple representing a ciphertext.      
    """
    # encode the integer into a plaintext polynomial
    s_time = time.time()
    m = np.array([pt] + [0] * (size - 1), dtype=np.int64) % t
    delta = q // t
    scaled_m = delta * m  % q
    e1 = gen_normal_poly(size)
    e2 = gen_normal_poly(size)
    u = gen_binary_poly(size)
    ct0 = polyadd(
            polyadd(
                polymul(pk[0], u, q, poly_mod),
                e1, q, poly_mod),
            scaled_m, q, poly_mod
        )
    ct1 = polyadd(
            polymul(pk[1], u, q, poly_mod),
            e2, q, poly_mod
        )
    cost = (time.time() - s_time) * 1000
    print("encrypt cost %sms" % cost)
    return (ct0, ct1)

def decrypt(sk, size, q, t, poly_mod, ct):
    """Decrypt a ciphertext
    Args:
        sk: secret-key.
        size: size of polynomials.
        q: ciphertext modulus.
        t: plaintext modulus.
        poly_mod: polynomial modulus.
        ct: ciphertext.
    Returns:
        Integer representing the plaintext.
    """
    s_time = time.time()
    scaled_pt = polyadd(
            polymul(ct[1], sk, q, poly_mod),
            ct[0], q, poly_mod
        )
    decrypted_poly = np.round(scaled_pt * t / q) % t
    cost = (time.time() - s_time) * 1000
    print("encrypt cost %sms" % cost)

    return int(decrypted_poly[0])