def negate(self, ct):
"""Negate a cipher i.e -(ct_value)
Args:
ct (Ciphertext): Ciphertext to be negated.
Returns:
A Ciphertext object with value equivalent to result of -(ct_value).
"""
result = copy.deepcopy(ct.data)
for i in range(len(result)):
for j in range(len(result[i])):
for k in range(len(result[i][j])):
result[i][j][k] = negate_mod(ct.data[i][j][k], self.coeff_modulus[j])
return CipherText(result)
def negate(self, ct):
"""Negate a cipher i.e -(ct_value)
Args:
ct (Ciphertext): Ciphertext to be negated.
Returns:
A Ciphertext object with value equivalent to result of -(ct_value).
"""
context_data = self.context.context_data_map[ct.param_id]
coeff_modulus = context_data.param.coeff_modulus
result = copy.deepcopy(ct.data)
for i in range(len(result)):
for j in range(len(coeff_modulus)):
for k in range(len(result[i][j])):
result[i][j][k] = negate_mod(result[i][j][k],
coeff_modulus[j])
return CipherText(result, ct.param_id)
def sm_mrq(self, input):
"""
Require: Input in base Bsk U {m_tilde}
Ensure: Output in base Bsk
"""
m_tilde_div_2 = self.m_tilde >> 1
result = []
# Compute r_m_tilde; The last component of the input is mod m_tilde
r_m_tilde = []
for i in range(self.coeff_count):
r_m_tilde.append(
negate_mod(
multiply_mod(input[-1][i], self.inv_prod_q_mod_m_tilde,
self.m_tilde),
self.m_tilde,
))
for k in range(self.base_Bsk.size):
base_Bsk_elt = self.base_Bsk.base[k]
inv_m_tilde_mod_Bsk_elt = self.inv_m_tilde_mod_Bsk[k]
prod_q_mod_Bsk_elt = self.prod_q_mod_Bsk[k]
temp_list = []
for i in range(self.coeff_count):
# We need centered reduction of r_m_tilde modulo Bsk. Note that m_tilde is chosen
# to be a power of two so we have '>=' below.
temp = r_m_tilde[i]
if temp >= m_tilde_div_2:
temp += base_Bsk_elt - self.m_tilde
# Compute (input + q*r_m_tilde)*m_tilde^(-1) mod Bsk
temp_list.append(((
(prod_q_mod_Bsk_elt * temp + input[k][i]) % base_Bsk_elt) *
inv_m_tilde_mod_Bsk_elt) % base_Bsk_elt)
result.append(temp_list)
return result
def __init__(self, encryption_param):
n = encryption_param.poly_modulus
q = encryption_param.coeff_modulus
t = encryption_param.plain_modulus
self._coeff_count = n
self.base_q = RNSBase(q)
self.base_q_size = len(q)
self._t = t
self._base_t_gamma = RNSBase([t, gamma])
self._base_t_gamma_size = 2
self.prod_t_gamma_mod_q = [(t * gamma) % q for q in self.base_q.base]
self._inv_gamma_mod_t = invert_mod(gamma, self._t)
# Compute -prod(q)^(-1) mod {t, gamma}
self.neg_inv_q_mod_t_gamma = [0] * self._base_t_gamma_size
for i in range(self._base_t_gamma_size):
self.neg_inv_q_mod_t_gamma[i] = self.base_q.base_prod % self._base_t_gamma.base[i]
self.neg_inv_q_mod_t_gamma[i] = invert_mod(
self.neg_inv_q_mod_t_gamma[i], self._base_t_gamma.base[i]
)
self.neg_inv_q_mod_t_gamma[i] = negate_mod(
self.neg_inv_q_mod_t_gamma[i], self._base_t_gamma.base[i]
)
def initialize(self):
base_q_size = len(self.q)
# In some cases we might need to increase the size of the base B by one, namely we require
# K*n*t*q^2<q*prod(B)*m_sk, where K takes into account cross terms when larger size
# ciphertexts are used, and n is the "delta factor" for the ring. We reserve 32 bits
# for K * n. Here the coeff modulus primes q_i are bounded to be
# SEAL_USER_MOD_BIT_COUNT_MAX (60) bits, and all primes in B and m_sk are
# SEAL_INTERNAL_MOD_BIT_COUNT (61) bits.
total_coeff_bit_count = RNSBase(self.q).base_prod.bit_length()
base_B_size = base_q_size
if 32 + self.t.bit_length() + total_coeff_bit_count >= 61 * len(
self.q) + 61:
base_B_size += 1
# Sample primes for B and two more primes: m_sk and gamma.
baseconv_primes = get_primes(self.coeff_count, 50, base_B_size + 2)
self.m_sk = baseconv_primes[0]
self.gamma = baseconv_primes[1]
base_B_primes = baseconv_primes[2:]
self.prod_t_gamma_mod_q = [(self.t * self.gamma) % q for q in self.q]
self.inv_gamma_mod_t = invert_mod(self.gamma, self.t)
# Set m_tilde_ to a non-prime value
self.m_tilde = 1 << 32
# Populate the base arrays
self.base_q = RNSBase(self.q)
self.base_B = RNSBase(base_B_primes)
self.base_Bsk = RNSBase(base_B_primes + [self.m_sk])
self.base_Bsk_m_tilde = RNSBase(base_B_primes + [self.m_sk] +
[self.m_tilde])
if self.t != 0:
self.base_t_gamma_size = 2
self.base_t_gamma = RNSBase([self.t, self.gamma])
# Set up BaseConvTool for q --> Bsk
self.base_q_to_Bsk_conv = BaseConvertor(self.base_q, self.base_Bsk)
# Set up BaseConvTool for q --> {m_tilde}
self.base_q_to_m_tilde_conv = BaseConvertor(self.base_q,
RNSBase([self.m_tilde]))
# Set up BaseConvTool for B --> q
self.base_B_to_q_conv = BaseConvertor(self.base_B, self.base_q)
# Set up BaseConvTool for B --> {m_sk}
self.base_B_to_m_sk_conv = BaseConvertor(self.base_B,
RNSBase([self.m_sk]))
if self.t != 0:
# Base conversion: convert from q to {t, gamma}
self.base_q_to_t_gamma_conv = BaseConvertor(
self.base_q, self.base_t_gamma)
# Compute prod(q)^(-1) mod m_tilde
inv_prod_q_mod_m_tilde = self.base_q.base_prod % self.m_tilde
self.inv_prod_q_mod_m_tilde = invert_mod(inv_prod_q_mod_m_tilde,
self.m_tilde)
# Compute m_tilde^(-1) mod Bsk
self.inv_m_tilde_mod_Bsk = [0] * self.base_Bsk.size
for i in range(self.base_Bsk.size):
self.inv_m_tilde_mod_Bsk[i] = invert_mod(
self.m_tilde % self.base_Bsk.base[i], self.base_Bsk.base[i])
# Compute prod(q) mod Bsk
self.prod_q_mod_Bsk = [0] * self.base_Bsk.size
for i in range(self.base_Bsk.size):
self.prod_q_mod_Bsk[
i] = self.base_q.base_prod % self.base_Bsk.base[i]
# Compute prod(B)^(-1) mod m_sk
self.inv_prod_B_mod_m_sk = self.base_B.base_prod % self.m_sk
self.inv_prod_B_mod_m_sk = invert_mod(self.inv_prod_B_mod_m_sk,
self.m_sk)
# Compute prod(B) mod q
self.prod_B_mod_q = [0] * self.base_q.size
for i in range(self.base_q.size):
self.prod_B_mod_q[i] = self.base_B.base_prod % self.base_q.base[i]
# Compute prod(q)^(-1) mod Bsk
self.inv_prod_q_mod_Bsk = [0] * self.base_Bsk.size
for i in range(self.base_Bsk.size):
self.inv_prod_q_mod_Bsk[
i] = self.base_q.base_prod % self.base_Bsk.base[i]
self.inv_prod_q_mod_Bsk[i] = invert_mod(self.inv_prod_q_mod_Bsk[i],
self.base_Bsk.base[i])
if self.t != 0:
# Compute -prod(q)^(-1) mod {t, gamma}
self.neg_inv_q_mod_t_gamma = [0] * self.base_t_gamma_size
for i in range(self.base_t_gamma_size):
self.neg_inv_q_mod_t_gamma[
i] = self.base_q.base_prod % self.base_t_gamma.base[i]
self.neg_inv_q_mod_t_gamma[i] = invert_mod(
self.neg_inv_q_mod_t_gamma[i], self.base_t_gamma.base[i])
self.neg_inv_q_mod_t_gamma[i] = negate_mod(
self.neg_inv_q_mod_t_gamma[i], self.base_t_gamma.base[i])
# Compute q[last]^(-1) mod q[i] for i = 0..last-1
# This is used by modulus switching and rescaling
self.inv_q_last_mod_q = [0] * (base_q_size - 1)
for i in range(base_q_size - 1):
self.inv_q_last_mod_q[i] = invert_mod(self.q[-1], self.q[i])
