tfhe 1.6.1

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

use crate::integer::ciphertext::{
    BaseRadixCiphertext, BaseSignedRadixCiphertext, CompressedModulusSwitchedRadixCiphertext,
    CompressedModulusSwitchedRadixCiphertextGeneric,
    CompressedModulusSwitchedSignedRadixCiphertext,
};
use crate::integer::{RadixCiphertext, ServerKey, SignedRadixCiphertext};
use crate::shortint::Ciphertext;
use rayon::prelude::*;

impl ServerKey {
    /// Compresses a ciphertext to have a smaller serialization size
    ///
    /// See [`CompressedModulusSwitchedRadixCiphertext#example`] for usage
    pub fn switch_modulus_and_compress_parallelized(
        &self,
        ct: &RadixCiphertext,
    ) -> CompressedModulusSwitchedRadixCiphertext {
        CompressedModulusSwitchedRadixCiphertext(
            self.switch_modulus_and_compress_generic_parallelized(&ct.blocks),
        )
    }
    /// Decompresses a compressed ciphertext
    /// This operation costs a PBS
    ///
    /// See [`CompressedModulusSwitchedRadixCiphertext#example`] for usage
    pub fn decompress_parallelized(
        &self,
        compressed_ct: &CompressedModulusSwitchedRadixCiphertext,
    ) -> RadixCiphertext {
        BaseRadixCiphertext {
            blocks: self.decompress_generic_parallelized(&compressed_ct.0),
        }
    }

    /// Compresses a signed ciphertext to have a smaller serialization size
    ///
    /// See [`CompressedModulusSwitchedSignedRadixCiphertext#example`] for usage
    pub fn switch_modulus_and_compress_signed_parallelized(
        &self,
        ct: &SignedRadixCiphertext,
    ) -> CompressedModulusSwitchedSignedRadixCiphertext {
        CompressedModulusSwitchedSignedRadixCiphertext(
            self.switch_modulus_and_compress_generic_parallelized(&ct.blocks),
        )
    }
    /// Decompresses a signed compressed ciphertext
    /// This operation costs a PBS
    ///
    /// See [`CompressedModulusSwitchedSignedRadixCiphertext#example`] for usage
    pub fn decompress_signed_parallelized(
        &self,
        compressed_ct: &CompressedModulusSwitchedSignedRadixCiphertext,
    ) -> SignedRadixCiphertext {
        BaseSignedRadixCiphertext {
            blocks: self.decompress_generic_parallelized(&compressed_ct.0),
        }
    }

    #[allow(clippy::int_plus_one)]
    fn switch_modulus_and_compress_generic_parallelized(
        &self,
        blocks: &[Ciphertext],
    ) -> CompressedModulusSwitchedRadixCiphertextGeneric {
        assert!(
            self.message_modulus().0 <= self.carry_modulus().0,
            "Compression does not support message_modulus > carry_modulus"
        );
        assert!(
            self.key.max_noise_level.get() >= self.message_modulus().0 + 1,
            "Compression does not support max_noise_level < message_modulus + 1"
        );

        let paired_blocks;

        let last_block;

        let len = blocks.len();

        if len.is_multiple_of(2) {
            paired_blocks = blocks;
            last_block = None;
        } else {
            paired_blocks = &blocks[..len - 1];
            last_block = Some(blocks.last().unwrap());
        }

        let paired_blocks = paired_blocks
            .par_chunks_exact(2)
            .map(|pair| {
                let mut packed = pair[0].clone();

                let scaled = self
                    .key
                    .unchecked_scalar_mul(&pair[1], self.message_modulus().0 as u8);

                self.key.unchecked_add_assign(&mut packed, &scaled);

                self.key.switch_modulus_and_compress(&packed)
            })
            .collect();

        let last_block = last_block.map(|a| self.key.switch_modulus_and_compress(a));

        CompressedModulusSwitchedRadixCiphertextGeneric {
            paired_blocks,
            last_block,
        }
    }

    fn decompress_generic_parallelized(
        &self,
        compressed_ct: &CompressedModulusSwitchedRadixCiphertextGeneric,
    ) -> Vec<Ciphertext> {
        let message_extract = self
            .key
            .generate_lookup_table(|x| x % self.message_modulus().0);

        let carry_extract = self
            .key
            .generate_lookup_table(|x| x / self.message_modulus().0);

        let mut blocks: Vec<Ciphertext> = compressed_ct
            .paired_blocks
            .par_iter()
            .flat_map(|a| {
                [
                    self.key
                        .decompress_and_apply_lookup_table(a, &message_extract),
                    self.key
                        .decompress_and_apply_lookup_table(a, &carry_extract),
                ]
            })
            .collect();

        if let Some(last_block) = compressed_ct.last_block.as_ref() {
            blocks.push(
                self.key
                    .decompress_and_apply_lookup_table(last_block, &message_extract),
            );
        }

        blocks
    }
}