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Code organisation for glwe
This commit is contained in:
Jean-Philippe Bossuat
@@ -1,304 +0,0 @@
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use crate::{AutomorphismKey, GLWECiphertext, GLWEOps, Infos, ScratchCore};
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use std::collections::HashMap;
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use backend::{FFT64, Module, Scratch};
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/// [StreamPacker] enables only the fly GLWE packing
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/// with constant memory of Log(N) ciphertexts.
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/// Main difference with usual GLWE packing is that
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/// the output is bit-reversed.
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pub struct StreamPacker {
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accumulators: Vec<Accumulator>,
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log_batch: usize,
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counter: usize,
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}
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/// [Accumulator] stores intermediate packing result.
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/// There are Log(N) such accumulators in a [StreamPacker].
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struct Accumulator {
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data: GLWECiphertext<Vec<u8>>,
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value: bool, // Implicit flag for zero ciphertext
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control: bool, // Can be combined with incoming value
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}
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impl Accumulator {
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/// Allocates a new [Accumulator].
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///
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/// #Arguments
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///
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/// * `module`: static backend FFT tables.
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/// * `basek`: base 2 logarithm of the GLWE ciphertext in memory digit representation.
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/// * `k`: base 2 precision of the GLWE ciphertext precision over the Torus.
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/// * `rank`: rank of the GLWE ciphertext.
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pub fn alloc(module: &Module<FFT64>, basek: usize, k: usize, rank: usize) -> Self {
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Self {
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data: GLWECiphertext::alloc(module, basek, k, rank),
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value: false,
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control: false,
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}
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}
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}
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impl StreamPacker {
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/// Instantiates a new [StreamPacker].
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///
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/// #Arguments
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///
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/// * `module`: static backend FFT tables.
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/// * `log_batch`: packs coefficients which are multiples of X^{N/2^log_batch}.
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/// i.e. with `log_batch=0` only the constant coefficient is packed
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/// and N GLWE ciphertext can be packed. With `log_batch=2` all coefficients
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/// which are multiples of X^{N/4} are packed. Meaning that N/4 ciphertexts
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/// can be packed.
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/// * `basek`: base 2 logarithm of the GLWE ciphertext in memory digit representation.
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/// * `k`: base 2 precision of the GLWE ciphertext precision over the Torus.
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/// * `rank`: rank of the GLWE ciphertext.
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pub fn new(module: &Module<FFT64>, log_batch: usize, basek: usize, k: usize, rank: usize) -> Self {
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let mut accumulators: Vec<Accumulator> = Vec::<Accumulator>::new();
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let log_n: usize = module.log_n();
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(0..log_n - log_batch).for_each(|_| accumulators.push(Accumulator::alloc(module, basek, k, rank)));
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Self {
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accumulators: accumulators,
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log_batch,
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counter: 0,
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}
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}
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/// Implicit reset of the internal state (to be called before a new packing procedure).
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pub fn reset(&mut self) {
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for i in 0..self.accumulators.len() {
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self.accumulators[i].value = false;
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self.accumulators[i].control = false;
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}
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self.counter = 0;
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}
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/// Number of scratch space bytes required to call [Self::add].
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pub fn scratch_space(module: &Module<FFT64>, basek: usize, ct_k: usize, k_ksk: usize, digits: usize, rank: usize) -> usize {
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pack_core_scratch_space(module, basek, ct_k, k_ksk, digits, rank)
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}
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pub fn galois_elements(module: &Module<FFT64>) -> Vec<i64> {
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GLWECiphertext::trace_galois_elements(module)
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}
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/// Adds a GLWE ciphertext to the [StreamPacker]. And propagates
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/// intermediate results among the [Accumulator]s.
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///
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/// #Arguments
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///
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/// * `module`: static backend FFT tables.
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/// * `res`: space to append fully packed ciphertext. Only when the number
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/// of packed ciphertexts reaches N/2^log_batch is a result written.
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/// * `a`: ciphertext to pack. Can optionally give None to pack a 0 ciphertext.
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/// * `auto_keys`: a [HashMap] containing the [AutomorphismKey]s.
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/// * `scratch`: scratch space of size at least [Self::add_scratch_space].
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pub fn add<DataA: AsRef<[u8]>, DataAK: AsRef<[u8]>>(
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&mut self,
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module: &Module<FFT64>,
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res: &mut Vec<GLWECiphertext<Vec<u8>>>,
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a: Option<&GLWECiphertext<DataA>>,
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auto_keys: &HashMap<i64, AutomorphismKey<DataAK, FFT64>>,
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scratch: &mut Scratch,
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) {
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pack_core(
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module,
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a,
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&mut self.accumulators,
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self.log_batch,
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auto_keys,
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scratch,
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);
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self.counter += 1 << self.log_batch;
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if self.counter == module.n() {
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res.push(
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self.accumulators[module.log_n() - self.log_batch - 1]
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.data
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.clone(),
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);
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self.reset();
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}
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}
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/// Flushes all accumlators and appends the result to `res`.
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pub fn flush<DataAK: AsRef<[u8]>>(
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&mut self,
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module: &Module<FFT64>,
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res: &mut Vec<GLWECiphertext<Vec<u8>>>,
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auto_keys: &HashMap<i64, AutomorphismKey<DataAK, FFT64>>,
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scratch: &mut Scratch,
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) {
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if self.counter != 0 {
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while self.counter != 0 {
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self.add(
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module,
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res,
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None::<&GLWECiphertext<Vec<u8>>>,
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auto_keys,
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scratch,
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);
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}
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}
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}
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}
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fn pack_core_scratch_space(module: &Module<FFT64>, basek: usize, ct_k: usize, k_ksk: usize, digits: usize, rank: usize) -> usize {
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combine_scratch_space(module, basek, ct_k, k_ksk, digits, rank)
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}
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fn pack_core<D: AsRef<[u8]>, DataAK: AsRef<[u8]>>(
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module: &Module<FFT64>,
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a: Option<&GLWECiphertext<D>>,
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accumulators: &mut [Accumulator],
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i: usize,
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auto_keys: &HashMap<i64, AutomorphismKey<DataAK, FFT64>>,
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scratch: &mut Scratch,
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) {
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let log_n: usize = module.log_n();
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if i == log_n {
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return;
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}
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// Isolate the first accumulator
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let (acc_prev, acc_next) = accumulators.split_at_mut(1);
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// Control = true accumlator is free to overide
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if !acc_prev[0].control {
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let acc_mut_ref: &mut Accumulator = &mut acc_prev[0]; // from split_at_mut
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// No previous value -> copies and sets flags accordingly
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if let Some(a_ref) = a {
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acc_mut_ref.data.copy(module, a_ref);
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acc_mut_ref.value = true
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} else {
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acc_mut_ref.value = false
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}
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acc_mut_ref.control = true; // Able to be combined on next call
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} else {
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// Compresses acc_prev <- combine(acc_prev, a).
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combine(module, &mut acc_prev[0], a, i, auto_keys, scratch);
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acc_prev[0].control = false;
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// Propagates to next accumulator
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if acc_prev[0].value {
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pack_core(
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module,
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Some(&acc_prev[0].data),
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acc_next,
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i + 1,
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auto_keys,
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scratch,
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);
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} else {
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pack_core(
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module,
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None::<&GLWECiphertext<Vec<u8>>>,
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acc_next,
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i + 1,
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auto_keys,
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scratch,
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);
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}
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}
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}
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fn combine_scratch_space(module: &Module<FFT64>, basek: usize, ct_k: usize, k_ksk: usize, digits: usize, rank: usize) -> usize {
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GLWECiphertext::bytes_of(module, basek, ct_k, rank)
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+ (GLWECiphertext::rsh_scratch_space(module)
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| GLWECiphertext::automorphism_scratch_space(module, basek, ct_k, ct_k, k_ksk, digits, rank))
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}
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/// [combine] merges two ciphertexts together.
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fn combine<D: AsRef<[u8]>, DataAK: AsRef<[u8]>>(
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module: &Module<FFT64>,
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acc: &mut Accumulator,
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b: Option<&GLWECiphertext<D>>,
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i: usize,
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auto_keys: &HashMap<i64, AutomorphismKey<DataAK, FFT64>>,
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scratch: &mut Scratch,
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) {
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let log_n: usize = module.log_n();
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let a: &mut GLWECiphertext<Vec<u8>> = &mut acc.data;
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let basek: usize = a.basek();
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let k: usize = a.k();
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let rank: usize = a.rank();
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let gal_el: i64;
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if i == 0 {
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gal_el = -1;
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} else {
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gal_el = module.galois_element(1 << (i - 1))
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}
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let t: i64 = 1 << (log_n - i - 1);
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// Goal is to evaluate: a = a + b*X^t + phi(a - b*X^t))
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// We also use the identity: AUTO(a * X^t, g) = -X^t * AUTO(a, g)
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// where t = 2^(log_n - i - 1) and g = 5^{2^(i - 1)}
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// Different cases for wether a and/or b are zero.
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//
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// Implicite RSH without modulus switch, introduces extra I(X) * Q/2 on decryption.
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// Necessary so that the scaling of the plaintext remains constant.
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// It however is ok to do so here because coefficients are eventually
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// either mapped to garbage or twice their value which vanishes I(X)
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// since 2*(I(X) * Q/2) = I(X) * Q = 0 mod Q.
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if acc.value {
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if let Some(b) = b {
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let (mut tmp_b, scratch_1) = scratch.tmp_glwe_ct(module, basek, k, rank);
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// a = a * X^-t
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a.rotate_inplace(module, -t);
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// tmp_b = a * X^-t - b
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tmp_b.sub(module, a, b);
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tmp_b.rsh(1, scratch_1);
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// a = a * X^-t + b
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a.add_inplace(module, b);
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a.rsh(1, scratch_1);
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tmp_b.normalize_inplace(module, scratch_1);
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// tmp_b = phi(a * X^-t - b)
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if let Some(key) = auto_keys.get(&gal_el) {
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tmp_b.automorphism_inplace(module, key, scratch_1);
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} else {
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panic!("auto_key[{}] not found", gal_el);
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}
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// a = a * X^-t + b - phi(a * X^-t - b)
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a.sub_inplace_ab(module, &tmp_b);
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a.normalize_inplace(module, scratch_1);
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// a = a + b * X^t - phi(a * X^-t - b) * X^t
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// = a + b * X^t - phi(a * X^-t - b) * - phi(X^t)
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// = a + b * X^t + phi(a - b * X^t)
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a.rotate_inplace(module, t);
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} else {
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a.rsh(1, scratch);
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// a = a + phi(a)
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if let Some(key) = auto_keys.get(&gal_el) {
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a.automorphism_add_inplace(module, key, scratch);
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} else {
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panic!("auto_key[{}] not found", gal_el);
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}
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}
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} else {
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if let Some(b) = b {
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let (mut tmp_b, scratch_1) = scratch.tmp_glwe_ct(module, basek, k, rank);
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tmp_b.rotate(module, 1 << (log_n - i - 1), b);
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tmp_b.rsh(1, scratch_1);
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// a = (b* X^t - phi(b* X^t))
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if let Some(key) = auto_keys.get(&gal_el) {
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a.automorphism_sub_ba::<&mut [u8], _>(module, &tmp_b, key, scratch_1);
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} else {
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panic!("auto_key[{}] not found", gal_el);
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}
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acc.value = true;
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}
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}
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}
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