Exemple #1
0
    def _sub_cipher_cipher(self, ct1, ct2):
        """Subtract two ciphertexts.

        Args:
            ct1 (Ciphertext): First polynomial argument (Minuend).
            ct2 (Ciphertext): Second polynomial argument (Subtrahend).

        Returns:
            A Ciphertext object with value equivalent to result of subtraction of two provided
                arguments.
        """
        ct1, ct2 = copy.deepcopy(ct1.data), copy.deepcopy(ct2.data)
        result = ct2 if len(ct2) > len(ct1) else ct1
        min_size, max_size = min(len(ct1), len(ct2)), max(len(ct1), len(ct2))

        for i in range(min_size):
            for j in range(len(self.coeff_modulus)):
                result[i][j] = poly_sub_mod(ct1[i][j], ct2[i][j],
                                            self.coeff_modulus[j],
                                            self.poly_modulus)

        for i in range(min_size + 1, max_size):
            for j in range(len(self.coeff_modulus)):
                result[i][j] = poly_negate_mod(result[i][j],
                                               self.coeff_modulus[j])

        return CipherText(result)
Exemple #2
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def encrypt_symmetric(context, secret_key):
    """Create encryption of zero values with a secret key which can be used in subsequent
    processes to add a message into it.

    Args:
        context (Context): A valid context required for extracting the encryption parameters.
        secret_key (SecretKey): A secret key generated with same encryption parameters.

    Returns:
        A ciphertext object containing encryption of zeroes by symmetric encryption procedure.
    """
    coeff_modulus = context.param.coeff_modulus
    coeff_mod_size = len(coeff_modulus)

    # Sample uniformly at random
    c1 = sample_poly_uniform(context.param)

    # Sample e <-- chi
    e = sample_poly_normal(context.param)

    # calculate -(a*s + e) (mod q) and store in c0

    c0 = [0] * coeff_mod_size

    for i in range(coeff_mod_size):
        c0[i] = poly_negate_mod(
            poly_add_mod(
                poly_mul_mod(c1[i], secret_key[i], coeff_modulus[i]), e[i], coeff_modulus[i]
            ),
            coeff_modulus[i],
        )

    return CipherText([c0, c1])
Exemple #3
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def test_poly_negate_mod(op1, mod, result):
    assert poly_negate_mod(op1, mod) == result