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fix: fix the atomic pattern used to cast in trivium and a test in shortint

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- parameters are optimized for a clean ciphertext, the ciphertext being
keyswitched was noisy
This commit is contained in:
Arthur Meyre
2025-02-27 11:16:55 +01:00
parent cba43c240e
commit aaf4cbaa65
2 changed files with 13 additions and 5 deletions
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11
apps/trivium/src/trans_ciphering/mod.rs
View File

@@ -48,6 +48,8 @@ fn transcipher_from_1_1_stream(
) -> FheUint64 {
assert_eq!(stream.len(), 64);
let id_lut = internal_server_key.generate_lookup_table(|x| x);
let pairs = (0..32)
.into_par_iter()
.map(|i| {
@@ -57,10 +59,11 @@ fn transcipher_from_1_1_stream(
let b0 = &stream[8 * byte_idx + 2 * pair_idx];
let b1 = &stream[8 * byte_idx + 2 * pair_idx + 1];
casting_key.cast(
&internal_server_key
.unchecked_add(b0, &internal_server_key.unchecked_scalar_mul(b1, 2)),
)
let mut combined = internal_server_key
.unchecked_add(b0, &internal_server_key.unchecked_scalar_mul(b1, 2));
internal_server_key.apply_lookup_table_assign(&mut combined, &id_lut);
casting_key.cast(&combined)
})
.collect::<Vec<_>>();

7
tfhe/src/shortint/key_switching_key/test.rs
View File

@@ -129,7 +129,12 @@ fn gen_multi_keys_test_add_with_overflow_ci_run_filter() {
let c3 = sk1.unchecked_scalar_mul(&c1, 2);
let c4 = sk1.unchecked_add(&c3, &c2);
let output_of_cast = ksk.cast(&c4);
// The optimized atomic pattern requires a ciphertext with NoiseLevel::NOMINAL, i.e. a
// ciphertext fresh out of a bootstrap
let id_lut = sk1.generate_lookup_table(|x| x);
let c5 = sk1.apply_lookup_table(&c4, &id_lut);
let output_of_cast = ksk.cast(&c5);
let clear = ck2.decrypt(&output_of_cast);
assert_eq!(clear, 3);
let ct_carry = sk2.carry_extract(&output_of_cast);