poulpy_core/
glwe_packing.rs

1use std::collections::HashMap;
2
3use poulpy_hal::{
4    api::ModuleLogN,
5    layouts::{Backend, GaloisElement, Module, Scratch},
6};
7
8use crate::{
9    GLWEAdd, GLWEAutomorphism, GLWECopy, GLWENormalize, GLWERotate, GLWEShift, GLWESub, GLWETrace, ScratchTakeCore,
10    layouts::{GGLWEInfos, GGLWEPreparedToRef, GLWE, GLWEAutomorphismKeyHelper, GLWEInfos, GLWEToMut, GetGaloisElement},
11};
12pub trait GLWEPacking<BE: Backend> {
13    fn glwe_pack_galois_elements(&self) -> Vec<i64>;
14
15    fn glwe_pack_tmp_bytes<R, K>(&self, res: &R, key: &K) -> usize
16    where
17        R: GLWEInfos,
18        K: GGLWEInfos;
19
20    /// Packs [x_0: GLWE(m_0), x_1: GLWE(m_1), ..., x_i: GLWE(m_i)]
21    /// to [0: GLWE(m_0 * X^x_0 + m_1 * X^x_1 + ... + m_i * X^x_i)]
22    fn glwe_pack<R, A, K, H>(
23        &self,
24        res: &mut R,
25        a: HashMap<usize, &mut A>,
26        log_gap_out: usize,
27        keys: &H,
28        scratch: &mut Scratch<BE>,
29    ) where
30        R: GLWEToMut + GLWEInfos,
31        A: GLWEToMut + GLWEInfos,
32        K: GGLWEPreparedToRef<BE> + GetGaloisElement + GGLWEInfos,
33        H: GLWEAutomorphismKeyHelper<K, BE>;
34}
35
36impl<BE: Backend> GLWEPacking<BE> for Module<BE>
37where
38    Self: GLWEAutomorphism<BE>
39        + GaloisElement
40        + ModuleLogN
41        + GLWERotate<BE>
42        + GLWESub
43        + GLWEShift<BE>
44        + GLWEAdd
45        + GLWENormalize<BE>
46        + GLWECopy
47        + GLWETrace<BE>,
48    Scratch<BE>: ScratchTakeCore<BE>,
49{
50    fn glwe_pack_galois_elements(&self) -> Vec<i64> {
51        self.glwe_trace_galois_elements()
52    }
53
54    fn glwe_pack_tmp_bytes<R, K>(&self, res: &R, key: &K) -> usize
55    where
56        R: GLWEInfos,
57        K: GGLWEInfos,
58    {
59        self.glwe_rotate_tmp_bytes()
60            .max(self.glwe_rsh_tmp_byte())
61            .max(self.glwe_normalize_tmp_bytes())
62            .max(self.glwe_automorphism_tmp_bytes(res, res, key))
63            + GLWE::bytes_of_from_infos(res)
64    }
65
66    /// Packs [x_0: GLWE(m_0), x_1: GLWE(m_1), ..., x_i: GLWE(m_i)]
67    /// to [0: GLWE(m_0 * X^x_0 + m_1 * X^x_1 + ... + m_i * X^x_i)]
68    fn glwe_pack<R, A, K, H>(
69        &self,
70        res: &mut R,
71        mut a: HashMap<usize, &mut A>,
72        log_gap_out: usize,
73        keys: &H,
74        scratch: &mut Scratch<BE>,
75    ) where
76        R: GLWEToMut + GLWEInfos,
77        A: GLWEToMut + GLWEInfos,
78        K: GGLWEPreparedToRef<BE> + GetGaloisElement + GGLWEInfos,
79        H: GLWEAutomorphismKeyHelper<K, BE>,
80    {
81        assert!(*a.keys().max().unwrap() < self.n());
82
83        let log_n: usize = self.log_n();
84
85        for i in 0..(log_n - log_gap_out) {
86            let t: usize = (1 << log_n).min(1 << (log_n - 1 - i));
87
88            let key: &K = if i == 0 {
89                keys.get_automorphism_key(-1).unwrap()
90            } else {
91                keys.get_automorphism_key(self.galois_element(1 << (i - 1)))
92                    .unwrap()
93            };
94
95            for j in 0..t {
96                let mut lo: Option<&mut A> = a.remove(&j);
97                let mut hi: Option<&mut A> = a.remove(&(j + t));
98
99                pack_internal(self, &mut lo, &mut hi, i, key, scratch);
100
101                if let Some(lo) = lo {
102                    a.insert(j, lo);
103                } else if let Some(hi) = hi {
104                    a.insert(j, hi);
105                }
106            }
107        }
108
109        self.glwe_trace(res, log_n - log_gap_out, *a.get(&0).unwrap(), keys, scratch);
110    }
111}
112
113#[allow(clippy::too_many_arguments)]
114fn pack_internal<M, A, B, K, BE: Backend>(
115    module: &M,
116    a: &mut Option<&mut A>,
117    b: &mut Option<&mut B>,
118    i: usize,
119    auto_key: &K,
120    scratch: &mut Scratch<BE>,
121) where
122    M: GLWEAutomorphism<BE> + GLWERotate<BE> + GLWESub + GLWEShift<BE> + GLWEAdd + GLWENormalize<BE>,
123    A: GLWEToMut + GLWEInfos,
124    B: GLWEToMut + GLWEInfos,
125    K: GGLWEPreparedToRef<BE> + GetGaloisElement + GGLWEInfos,
126    Scratch<BE>: ScratchTakeCore<BE>,
127{
128    // Goal is to evaluate: a = a + b*X^t + phi(a - b*X^t))
129    // We also use the identity: AUTO(a * X^t, g) = -X^t * AUTO(a, g)
130    // where t = 2^(log_n - i - 1) and g = 5^{2^(i - 1)}
131    // Different cases for wether a and/or b are zero.
132    //
133    // Implicite RSH without modulus switch, introduces extra I(X) * Q/2 on decryption.
134    // Necessary so that the scaling of the plaintext remains constant.
135    // It however is ok to do so here because coefficients are eventually
136    // either mapped to garbage or twice their value which vanishes I(X)
137    // since 2*(I(X) * Q/2) = I(X) * Q = 0 mod Q.
138    if let Some(a) = a.as_deref_mut() {
139        let t: i64 = 1 << (a.n().log2() - i - 1);
140
141        if let Some(b) = b.as_deref_mut() {
142            let (mut tmp_b, scratch_1) = scratch.take_glwe(a);
143
144            // a = a * X^-t
145            module.glwe_rotate_inplace(-t, a, scratch_1);
146
147            // tmp_b = a * X^-t - b
148            module.glwe_sub(&mut tmp_b, a, b);
149            module.glwe_rsh(1, &mut tmp_b, scratch_1);
150
151            // a = a * X^-t + b
152            module.glwe_add_inplace(a, b);
153            module.glwe_rsh(1, a, scratch_1);
154
155            module.glwe_normalize_inplace(&mut tmp_b, scratch_1);
156
157            // tmp_b = phi(a * X^-t - b)
158            module.glwe_automorphism_inplace(&mut tmp_b, auto_key, scratch_1);
159
160            // a = a * X^-t + b - phi(a * X^-t - b)
161            module.glwe_sub_inplace(a, &tmp_b);
162            module.glwe_normalize_inplace(a, scratch_1);
163
164            // a = a + b * X^t - phi(a * X^-t - b) * X^t
165            //   = a + b * X^t - phi(a * X^-t - b) * - phi(X^t)
166            //   = a + b * X^t + phi(a - b * X^t)
167            module.glwe_rotate_inplace(t, a, scratch_1);
168        } else {
169            module.glwe_rsh(1, a, scratch);
170            // a = a + phi(a)
171            module.glwe_automorphism_add_inplace(a, auto_key, scratch);
172        }
173    } else if let Some(b) = b.as_deref_mut() {
174        let t: i64 = 1 << (b.n().log2() - i - 1);
175
176        let (mut tmp_b, scratch_1) = scratch.take_glwe(b);
177        module.glwe_rotate(t, &mut tmp_b, b);
178        module.glwe_rsh(1, &mut tmp_b, scratch_1);
179
180        // a = (b* X^t - phi(b* X^t))
181        module.glwe_automorphism_sub_negate(b, &tmp_b, auto_key, scratch_1);
182    }
183}
poulpy_core/glwe_packing.rs

poulpy_core/
glwe_packing.rs
