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Enable BMMP as on/off switch "use_bmmp". #49

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Enable BMMP as on/off switch "use_bmmp". #49

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136 changes: 88 additions & 48 deletions jaxite/jaxite_lib/bootstrap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,13 +31,15 @@ class BootstrappingKey:
"""An array with row j an RGSW encryption of bit j of an LWE secret key."""

encrypted_lwe_sk_bits: jnp.ndarray
use_bmmp: bool = True


def gen_bootstrapping_key(
lwe_sk: lwe.LweSecretKey,
rgsw_sk: rgsw.RgswSecretKey,
decomposition_params: decomposition.DecompositionParameters,
prg: random_source.RandomSource,
use_bmmp: bool = True,
) -> BootstrappingKey:
"""Generate a bootstrapping key for the given LWE secret key.

Expand All @@ -64,7 +66,11 @@ def gen_bootstrapping_key(
"requires an even lwe_sk dimension, but got "
f"{lwe_sk_dim}"
)
num_bsk_encryptions = lwe_sk_dim + lwe_sk_dim // 2

if use_bmmp:
num_bsk_encryptions = lwe_sk_dim + lwe_sk_dim // 2
else:
num_bsk_encryptions = lwe_sk_dim

ai_samples = prg.uniform(
shape=(
Expand All @@ -81,30 +87,36 @@ def gen_bootstrapping_key(
dtype=jnp.uint32,
)

# Using the improved blind rotate from Bourse-Minelli-Minihold-Paillier
# (BMMP17: https://eprint.iacr.org/2017/1114), a trick uses a larger
# bootstrapping key to reduce the number of external products required by 1/2.
# Rather than encrypt the secret key bits of the LWE key separately, we
# encrypt:
#
# BSK_{3i} = s_{2i} * s_{2i+1},
# BSK_{3i+1} = s_{2i} * (1 − s_{2i+1}),
# BSK_{3i+2} = (1 − s_{2i}) * s_{2i+1}
#
# which enables a bootstrap operation that involves 1/2 as many external
# products, though this causes the bootstrapping key to be 50% larger.
lwe_sk_data = lwe_sk.key_data.astype(jnp.uint32)
bsk_input_pairs = jnp.zeros(num_bsk_encryptions, dtype=jnp.uint32)

bsk_input_pairs = bsk_input_pairs.at[::3].set(
jnp.multiply(lwe_sk_data[::2], lwe_sk_data[1::2])
)
bsk_input_pairs = bsk_input_pairs.at[1::3].set(
jnp.multiply(lwe_sk_data[::2], 1 - lwe_sk_data[1::2])
)
bsk_input_pairs = bsk_input_pairs.at[2::3].set(
jnp.multiply(1 - lwe_sk_data[::2], lwe_sk_data[1::2])
)
# boostrapping key encrypted each of the security key
# BMMP groups multiple secrutiy keys together into a single BSK. (1.5N v.s N)
if use_bmmp:
# Using the improved blind rotate from Bourse-Minelli-Minihold-Paillier
# (BMMP17: https://eprint.iacr.org/2017/1114), a trick uses a larger
# bootstrapping key to reduce the number of external products required by
# 1/2. Rather than encrypt the secret key bits of the LWE key separately,
# we encrypt:
#
# BSK_{3i} = s_{2i} * s_{2i+1},
# BSK_{3i+1} = s_{2i} * (1 − s_{2i+1}),
# BSK_{3i+2} = (1 − s_{2i}) * s_{2i+1}
#
# which enables a bootstrap operation that involves 1/2 as many external
# products, though this causes the bootstrapping key to be 50% larger.
bsk_input_pairs = jnp.zeros(num_bsk_encryptions, dtype=jnp.uint32)
bsk_input_pairs = bsk_input_pairs.at[::3].set(
jnp.multiply(lwe_sk_data[::2], lwe_sk_data[1::2])
)
bsk_input_pairs = bsk_input_pairs.at[1::3].set(
jnp.multiply(lwe_sk_data[::2], 1 - lwe_sk_data[1::2])
)
bsk_input_pairs = bsk_input_pairs.at[2::3].set(
jnp.multiply(1 - lwe_sk_data[::2], lwe_sk_data[1::2])
)
else:
# BSK_{i} = s_{i},
bsk_input_pairs = lwe_sk_data

# Applying vmap to the entire jit_encrypt over all sk bits will exhaust the
# tensor core's memory with prod security parameters. It will eagerly allocate
Expand Down Expand Up @@ -171,11 +183,13 @@ def process_one_batch(i):
rlwe_sk.modulus_degree,
))

return BootstrappingKey(encrypted_lwe_sk_bits=encrypted_lwe_sk_bits)
return BootstrappingKey(
encrypted_lwe_sk_bits=encrypted_lwe_sk_bits, use_bmmp=use_bmmp
)


@jax.named_call
@functools.partial(jax.jit, static_argnums=(4, 5, 6))
@functools.partial(jax.jit, static_argnums=(4, 5, 6, 7))
def jit_bootstrap(
ciphertext: types.LweCiphertext,
test_poly_ciphertext_message: jnp.ndarray,
Expand All @@ -184,6 +198,7 @@ def jit_bootstrap(
ks_decomposition_params: decomposition.DecompositionParameters,
bs_decomposition_params: decomposition.DecompositionParameters,
scheme_params: parameters.SchemeParameters,
bsk_use_bmmp: bool = True,
) -> types.LweCiphertext:
"""Apply functional bootstrap to reduce noise in the input ciphertext.

Expand Down Expand Up @@ -220,6 +235,7 @@ def jit_bootstrap(
test_poly_ciphertext_message,
approx_ciphertext,
bsk_encrypted_lwe_sk_bits,
bsk_use_bmmp,
test_poly_log_coefficient_modulus,
bs_decomposition_params,
)
Expand Down Expand Up @@ -290,6 +306,7 @@ def bootstrap(
test_poly_ciphertext.message,
approx_ciphertext,
bsk.encrypted_lwe_sk_bits,
bsk.use_bmmp,
test_poly_log_coefficient_modulus,
bs_decomposition_params,
)
Expand Down Expand Up @@ -436,6 +453,7 @@ def blind_rotate(
rot_polynomial.message,
coefficient_index,
bsk.encrypted_lwe_sk_bits,
bsk.use_bmmp,
rot_polynomial.log_coefficient_modulus,
decomposition_params,
)
Expand All @@ -447,11 +465,12 @@ def blind_rotate(


@jax.named_call
@functools.partial(jax.jit, static_argnums=(3, 4))
@functools.partial(jax.jit, static_argnums=(3, 4, 5))
def jit_blind_rotate(
rot_polynomial: jnp.ndarray,
coefficient_index: types.LweCiphertext,
bsk: jnp.ndarray,
use_bmmp: bool,
log_coefficient_modulus: int,
decomposition_params: decomposition.DecompositionParameters,
) -> rlwe.RlweCiphertext:
Expand All @@ -467,30 +486,51 @@ def jit_blind_rotate(
# Using the improved blind rotate from Bourse-Minelli-Minihold-Paillier
# (BMMP17: https://eprint.iacr.org/2017/1114), a trick uses a larger
# bootstrapping key to reduce the number of external products required by 1/2.
num_loop_terms = (coefficient_index.shape[0] - 1) // 2
if use_bmmp:
num_loop_terms = (coefficient_index.shape[0] - 1) // 2
else:
num_loop_terms = coefficient_index.shape[0] - 1

def one_external_product(j, c_prime_accum):
# Doing this computation inside the external product loop improves cache
# locality, resulting in reduced data copying.
power1 = coefficient_index[2 * j] + coefficient_index[2 * j + 1]
power2 = coefficient_index[2 * j]
power3 = coefficient_index[2 * j + 1]
bmmp_factor = (
matrix_utils.scale_by_x_power_n_minus_1(
power1, bsk[3 * j], log_modulus=log_coefficient_modulus
)
+ matrix_utils.scale_by_x_power_n_minus_1(
power2, bsk[3 * j + 1], log_modulus=log_coefficient_modulus
)
+ matrix_utils.scale_by_x_power_n_minus_1(
power3, bsk[3 * j + 2], log_modulus=log_coefficient_modulus
)
).astype(jnp.uint32)
return c_prime_accum + jit_external_product(
rgsw_ct=bmmp_factor,
rlwe_ct=c_prime_accum,
decomposition_params=decomposition_params,
)
if use_bmmp:
# Doing this computation inside the external product loop improves cache
# locality, resulting in reduced data copying.
power1 = coefficient_index[2 * j] + coefficient_index[2 * j + 1]
power2 = coefficient_index[2 * j]
power3 = coefficient_index[2 * j + 1]
bmmp_factor = (
matrix_utils.scale_by_x_power_n_minus_1( # Rotation.
power1, bsk[3 * j], log_modulus=log_coefficient_modulus
)
+ matrix_utils.scale_by_x_power_n_minus_1(
power2, bsk[3 * j + 1], log_modulus=log_coefficient_modulus
)
+ matrix_utils.scale_by_x_power_n_minus_1(
power3, bsk[3 * j + 2], log_modulus=log_coefficient_modulus
)
).astype(jnp.uint32)
return c_prime_accum + jit_external_product(
rgsw_ct=bmmp_factor,
rlwe_ct=c_prime_accum,
decomposition_params=decomposition_params,
)
# c'_mul = c' * X^{a_j^tilde} (for each entry in c')
else:
# where a_j^tilde = coefficient_index[j] #Disabled BMMP
c_prime_mul = matrix_utils.monomial_mul_list(
c_prime_accum,
coefficient_index[j],
log_coefficient_modulus,
).astype(jnp.uint32)

# Update c_prime with the output of the CMUX operation, where either
# `c_prime` or `c_prime * X^{a_j^tilde}` is chosen by `bsk` at index j.
return jit_cmux(
control=bsk[j],
eq_zero=c_prime_accum,
neq_zero=c_prime_mul,
decomposition_params=decomposition_params,
)

return jax.lax.fori_loop(0, num_loop_terms, one_external_product, c_prime)

Expand Down
18 changes: 12 additions & 6 deletions jaxite/jaxite_lib/bootstrap_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@ def run_bootstrap_test(
padding_bits: int,
rlwe_rng: random_source.RandomSource,
skip_assert: bool = False,
use_bmmp: bool = False,
):
cleartext = 2**message_bits - 1
test_utils.assert_safe_modulus_switch(
Expand Down Expand Up @@ -77,6 +78,7 @@ def run_bootstrap_test(
rgsw_sk=rgsw_key,
decomposition_params=test_utils.BSK_DECOMP_PARAMS_128_BIT_SECURITY,
prg=rlwe_rng,
use_bmmp=use_bmmp,
)
ksk = key_switch.gen_key(
in_key=rlwe.flatten_key(rlwe_key),
Expand Down Expand Up @@ -120,6 +122,7 @@ def run_bootstrap_test(
test_utils.KSK_DECOMP_PARAMS_128_BIT_SECURITY,
test_utils.BSK_DECOMP_PARAMS_128_BIT_SECURITY,
scheme_parameters,
bsk.use_bmmp,
)

self.assertEqual(len(jit_bootstrapped), len(bootstrapped))
Expand Down Expand Up @@ -147,12 +150,11 @@ def run_bootstrap_test(


@parameterized.product(
log_ai_bound=_LOG_AI_BOUNDS,
seed=_SEEDS,
log_ai_bound=_LOG_AI_BOUNDS, seed=_SEEDS, use_bmmp=[True, False]
)
class BootstrapTest(BootstrapBaseTest):

def test_3_bit_bootstrap(self, log_ai_bound, seed):
def test_3_bit_bootstrap(self, log_ai_bound, seed, use_bmmp):
message_bits = 3
padding_bits = 1
lwe_dimension = 4
Expand All @@ -173,10 +175,11 @@ def test_3_bit_bootstrap(self, log_ai_bound, seed):
mod_degree=mod_degree,
padding_bits=padding_bits,
rlwe_rng=rng,
use_bmmp=use_bmmp,
)

def test_3_bit_bootstrap_larger_lwe_dimension(
self, log_ai_bound: int, seed: int
self, log_ai_bound: int, seed: int, use_bmmp: bool
):
message_bits = 3
padding_bits = 1
Expand All @@ -200,10 +203,11 @@ def test_3_bit_bootstrap_larger_lwe_dimension(
mod_degree=mod_degree,
padding_bits=padding_bits,
rlwe_rng=rng,
use_bmmp=use_bmmp,
)

@absltest.skip("b/325287870")
def test_6_bit_bootstrap(self, log_ai_bound: int, seed: int):
def test_6_bit_bootstrap(self, log_ai_bound: int, seed: int, use_bmmp: bool):
message_bits = 6
padding_bits = 1
lwe_dimension = 30
Expand All @@ -224,10 +228,11 @@ def test_6_bit_bootstrap(self, log_ai_bound: int, seed: int):
mod_degree=mod_degree,
padding_bits=padding_bits,
rlwe_rng=rng,
use_bmmp=use_bmmp,
)

def test_3_bit_bootstrap_prod_decomp_params(
self, log_ai_bound: int, seed: int
self, log_ai_bound: int, seed: int, use_bmmp: bool
):
message_bits = 3
padding_bits = 1
Expand All @@ -249,6 +254,7 @@ def test_3_bit_bootstrap_prod_decomp_params(
mod_degree=mod_degree,
padding_bits=padding_bits,
rlwe_rng=rng,
use_bmmp=use_bmmp,
)


Expand Down
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