tfhe 1.6.0

TFHE-rs is a fully homomorphic encryption (FHE) library that implements Zama's variant of TFHE.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226

use crate::core_crypto::algorithms::lwe_encryption::decrypt_lwe_ciphertext;
use crate::core_crypto::algorithms::test::noise_distribution::lwe_encryption_noise::lwe_compact_public_key_encryption_expected_variance;
use crate::core_crypto::commons::dispersion::DispersionParameter;
use crate::core_crypto::commons::math::random::DynamicDistribution;
use crate::core_crypto::commons::test_tools::{gaussian_variance_confidence_interval, variance};
use crate::prelude::*;
use crate::shortint::parameters::compact_public_key_only::CompactCiphertextListExpansionKind;
use crate::shortint::parameters::test_params::{
    TEST_PARAM_KEYSWITCH_PKE_TO_BIG_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
    TEST_PARAM_KEYSWITCH_PKE_TO_SMALL_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
    TEST_PARAM_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
    TEST_PARAM_PKE_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
};
use crate::shortint::parameters::{
    AtomicPatternParameters, ClassicPBSParameters, CompactPublicKeyEncryptionParameters,
    ShortintKeySwitchingParameters,
};
use crate::{ClientKey, CompactCiphertextList, CompactPublicKey, ConfigBuilder, FheUint2};

use rayon::prelude::*;

#[test]
fn test_noise_check_secret_key_encryption_noise_tuniform() {
    let params: AtomicPatternParameters = TEST_PARAM_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128.into();

    let modulus_as_f64 = params.ciphertext_modulus().raw_modulus_float();

    let encryption_noise = params.encryption_noise_distribution();

    let (inclusive_min_val, inclusive_max_val, expected_variance) = match encryption_noise {
        DynamicDistribution::Gaussian(_gaussian) => {
            panic!("This test is written for TUniform, wrong parameter set used")
        }
        DynamicDistribution::TUniform(tuniform) => (
            tuniform.min_value_inclusive(),
            tuniform.max_value_inclusive(),
            tuniform.variance(modulus_as_f64),
        ),
    };

    let config = ConfigBuilder::with_custom_parameters(params).build();

    const NB_TEST: usize = 125_000;

    let noise_samples: Vec<_> = (0..NB_TEST)
        .into_par_iter()
        .map(|_| {
            let cks = ClientKey::generate(config);
            let encrypted = FheUint2::encrypt(0u32, &cks);

            // Drop to lower level APIs to get to the noise
            let integer_key = cks.into_raw_parts().0;
            let shortint_key: &crate::shortint::ClientKey = integer_key.as_ref();

            let radix = encrypted.into_raw_parts().0;
            assert!(radix.blocks.len() == 1);
            let shortint_block = radix.blocks.into_iter().next().unwrap();

            let noise = shortint_key.decrypt_no_decode(&shortint_block);
            let signed_noise: i64 = noise.0 as i64;

            assert!(
                signed_noise >= inclusive_min_val,
                "{signed_noise} is not >= {inclusive_min_val}"
            );

            assert!(
                signed_noise <= inclusive_max_val,
                "{signed_noise} is not <= {inclusive_max_val}"
            );

            // Rescale
            signed_noise as f64 / modulus_as_f64
        })
        .collect();

    let measured_variance = variance(&noise_samples);
    // With our test settings this gives a range of around 2/100 of a bit, this should be accurate
    // enough, so if the expected result is res and log2(res) == 10.00 then interval will be about
    // [9.99; 10.01]
    let measured_confidence_interval =
        gaussian_variance_confidence_interval(noise_samples.len() as f64, measured_variance, 0.999);

    // For --no-capture inspection
    println!("measured_variance={measured_variance:?}");
    println!("expected_variance={expected_variance:?}");
    println!(
        "lower_bound={:?}",
        measured_confidence_interval.lower_bound()
    );
    println!(
        "upper_bound={:?}",
        measured_confidence_interval.upper_bound()
    );

    assert!(measured_confidence_interval.variance_is_in_interval(expected_variance));
}

#[test]
fn test_noise_check_compact_public_key_to_small_encryption_noise_tuniform() {
    noise_check_compact_public_key_encryption_noise_tuniform(
        TEST_PARAM_PKE_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
        TEST_PARAM_KEYSWITCH_PKE_TO_SMALL_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
        TEST_PARAM_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
    )
}

#[test]
fn test_noise_check_compact_public_key_to_big_encryption_noise_tuniform() {
    noise_check_compact_public_key_encryption_noise_tuniform(
        TEST_PARAM_PKE_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
        TEST_PARAM_KEYSWITCH_PKE_TO_BIG_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
        TEST_PARAM_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128,
    )
}

fn noise_check_compact_public_key_encryption_noise_tuniform(
    mut cpke_params: CompactPublicKeyEncryptionParameters,
    ksk_params: ShortintKeySwitchingParameters,
    block_params: ClassicPBSParameters,
) {
    // Hack to avoid server key needs and get the ciphertext directly
    cpke_params.expansion_kind =
        CompactCiphertextListExpansionKind::NoCasting(block_params.atomic_pattern());

    let modulus_as_f64 = cpke_params.ciphertext_modulus.raw_modulus_float();

    let encryption_noise = cpke_params.encryption_noise_distribution;
    let encryption_variance = match encryption_noise {
        DynamicDistribution::Gaussian(gaussian) => gaussian.standard_dev().get_variance(),
        DynamicDistribution::TUniform(tuniform) => tuniform.variance(modulus_as_f64),
    };

    let expected_variance = lwe_compact_public_key_encryption_expected_variance(
        encryption_variance,
        cpke_params.encryption_lwe_dimension,
    );

    let config = ConfigBuilder::with_custom_parameters(block_params)
        .use_dedicated_compact_public_key_parameters((cpke_params, ksk_params))
        .build();

    const NB_TEST: usize = 125_000;

    let thread_pools: Vec<_> = (0..rayon::current_num_threads())
        .map(|_| {
            rayon::ThreadPoolBuilder::new()
                .num_threads(1)
                .build()
                .unwrap()
        })
        .collect();

    let pool_count = thread_pools.len();

    // Div_ceil to be sure the product of pools * chunk_size can be a bit above NB_TEST
    // Then the chunking logic will keep it == to NB_TEST
    let chunk_size = NB_TEST.div_ceil(pool_count);

    let noise_samples: Vec<_> = thread_pools
        .into_par_iter()
        .zip((0..NB_TEST).into_par_iter().chunks(chunk_size))
        .flat_map(|(pool, work_idx)| {
            pool.install(|| {
                work_idx
                    .into_iter()
                    .map(|_| {
                        let cks = ClientKey::generate(config);
                        let cpk = CompactPublicKey::new(&cks);

                        let mut builder = CompactCiphertextList::builder(&cpk);
                        builder
                            .push_with_num_bits(
                                0u32,
                                cpke_params.message_modulus.0.ilog2() as usize,
                            )
                            .unwrap();
                        let list = builder.build();
                        let expanded = list.expand().unwrap();
                        let encrypted: FheUint2 = expanded.get(0).unwrap().unwrap();

                        // Drop to lower level APIs to get to the noise
                        let integer_key = cks.into_raw_parts().1.unwrap().0;
                        let shortint_key = integer_key.into_raw_parts();
                        let core_key = shortint_key.into_raw_parts().0;

                        let radix = encrypted.into_raw_parts().0;
                        assert!(radix.blocks.len() == 1);
                        let shortint_block = radix.blocks.into_iter().next().unwrap();
                        let lwe_ct = shortint_block.ct;

                        // This is directly the noise as we encrypted a 0
                        let noise = decrypt_lwe_ciphertext(&core_key, &lwe_ct).0;
                        let signed_noise: i64 = noise as i64;

                        // Rescale
                        signed_noise as f64 / modulus_as_f64
                    })
                    .collect::<Vec<_>>()
            })
        })
        .collect();

    assert_eq!(noise_samples.len(), NB_TEST);

    let measured_variance = variance(&noise_samples);
    // With our test settings this gives a range of around 2/100 of a bit, this should be accurate
    // enough, so if the expected result is res and log2(res) == 10.00 then interval will be about
    // [9.99; 10.01]
    let measured_confidence_interval =
        gaussian_variance_confidence_interval(noise_samples.len() as f64, measured_variance, 0.999);

    // For --no-capture inspection
    println!("measured_variance={measured_variance:?}");
    println!("expected_variance={expected_variance:?}");
    println!(
        "lower_bound={:?}",
        measured_confidence_interval.lower_bound()
    );
    println!(
        "upper_bound={:?}",
        measured_confidence_interval.upper_bound()
    );

    assert!(measured_confidence_interval.variance_is_in_interval(expected_variance));
}