1073 lines
32 KiB
C
1073 lines
32 KiB
C
/*
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* Falcon signature generation.
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*
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* ==========================(LICENSE BEGIN)============================
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*
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* Copyright (c) 2017-2019 Falcon Project
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*
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* ===========================(LICENSE END)=============================
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*
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* @author Thomas Pornin <thomas.pornin@nccgroup.com>
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*/
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#include "inner.h"
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/* =================================================================== */
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/*
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* Compute degree N from logarithm 'logn'.
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*/
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#define MKN(logn) ((size_t)1 << (logn))
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/* =================================================================== */
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/*
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* Binary case:
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* N = 2^logn
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* phi = X^N+1
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*/
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/*
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* Get the size of the LDL tree for an input with polynomials of size
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* 2^logn. The size is expressed in the number of elements.
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*/
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static inline unsigned
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ffLDL_treesize(unsigned logn) {
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/*
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* For logn = 0 (polynomials are constant), the "tree" is a
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* single element. Otherwise, the tree node has size 2^logn, and
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* has two child trees for size logn-1 each. Thus, treesize s()
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* must fulfill these two relations:
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*
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* s(0) = 1
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* s(logn) = (2^logn) + 2*s(logn-1)
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*/
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return (logn + 1) << logn;
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}
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/*
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* Inner function for ffLDL_fft(). It expects the matrix to be both
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* auto-adjoint and quasicyclic; also, it uses the source operands
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* as modifiable temporaries.
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*
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* tmp[] must have room for at least one polynomial.
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*/
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static void
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ffLDL_fft_inner(fpr *tree,
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fpr *g0, fpr *g1, unsigned logn, fpr *tmp) {
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size_t n, hn;
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n = MKN(logn);
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if (n == 1) {
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tree[0] = g0[0];
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return;
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}
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hn = n >> 1;
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/*
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* The LDL decomposition yields L (which is written in the tree)
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* and the diagonal of D. Since d00 = g0, we just write d11
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* into tmp.
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*/
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PQCLEAN_FALCON512_CLEAN_poly_LDLmv_fft(tmp, tree, g0, g1, g0, logn);
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/*
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* Split d00 (currently in g0) and d11 (currently in tmp). We
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* reuse g0 and g1 as temporary storage spaces:
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* d00 splits into g1, g1+hn
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* d11 splits into g0, g0+hn
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*/
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(g1, g1 + hn, g0, logn);
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(g0, g0 + hn, tmp, logn);
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/*
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* Each split result is the first row of a new auto-adjoint
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* quasicyclic matrix for the next recursive step.
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*/
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ffLDL_fft_inner(tree + n,
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g1, g1 + hn, logn - 1, tmp);
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ffLDL_fft_inner(tree + n + ffLDL_treesize(logn - 1),
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g0, g0 + hn, logn - 1, tmp);
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}
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/*
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* Compute the ffLDL tree of an auto-adjoint matrix G. The matrix
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* is provided as three polynomials (FFT representation).
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*
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* The "tree" array is filled with the computed tree, of size
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* (logn+1)*(2^logn) elements (see ffLDL_treesize()).
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*
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* Input arrays MUST NOT overlap, except possibly the three unmodified
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* arrays g00, g01 and g11. tmp[] should have room for at least three
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* polynomials of 2^logn elements each.
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*/
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static void
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ffLDL_fft(fpr *tree, const fpr *g00,
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const fpr *g01, const fpr *g11,
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unsigned logn, fpr *tmp) {
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size_t n, hn;
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fpr *d00, *d11;
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n = MKN(logn);
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if (n == 1) {
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tree[0] = g00[0];
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return;
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}
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hn = n >> 1;
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d00 = tmp;
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d11 = tmp + n;
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tmp += n << 1;
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memcpy(d00, g00, n * sizeof * g00);
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PQCLEAN_FALCON512_CLEAN_poly_LDLmv_fft(d11, tree, g00, g01, g11, logn);
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(tmp, tmp + hn, d00, logn);
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(d00, d00 + hn, d11, logn);
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memcpy(d11, tmp, n * sizeof * tmp);
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ffLDL_fft_inner(tree + n,
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d11, d11 + hn, logn - 1, tmp);
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ffLDL_fft_inner(tree + n + ffLDL_treesize(logn - 1),
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d00, d00 + hn, logn - 1, tmp);
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}
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/*
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* Normalize an ffLDL tree: each leaf of value x is replaced with
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* sigma / sqrt(x).
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*/
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static void
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ffLDL_binary_normalize(fpr *tree, unsigned logn) {
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/*
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* TODO: make an iterative version.
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*/
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size_t n;
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n = MKN(logn);
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if (n == 1) {
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/*
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* We actually store in the tree leaf the inverse of
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* the value mandated by the specification: this
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* saves a division both here and in the sampler.
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*/
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tree[0] = fpr_mul(fpr_sqrt(tree[0]), fpr_inv_sigma);
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} else {
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ffLDL_binary_normalize(tree + n, logn - 1);
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ffLDL_binary_normalize(tree + n + ffLDL_treesize(logn - 1),
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logn - 1);
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}
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}
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/* =================================================================== */
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/*
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* Convert an integer polynomial (with small values) into the
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* representation with complex numbers.
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*/
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static void
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smallints_to_fpr(fpr *r, const int8_t *t, unsigned logn) {
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size_t n, u;
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n = MKN(logn);
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for (u = 0; u < n; u ++) {
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r[u] = fpr_of(t[u]);
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}
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}
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/*
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* The expanded private key contains:
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* - The B0 matrix (four elements)
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* - The ffLDL tree
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*/
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static inline size_t
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skoff_b00(unsigned logn) {
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(void)logn;
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return 0;
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}
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static inline size_t
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skoff_b01(unsigned logn) {
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return MKN(logn);
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}
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static inline size_t
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skoff_b10(unsigned logn) {
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return 2 * MKN(logn);
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}
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static inline size_t
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skoff_b11(unsigned logn) {
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return 3 * MKN(logn);
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}
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static inline size_t
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skoff_tree(unsigned logn) {
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return 4 * MKN(logn);
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}
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/* see inner.h */
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void
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PQCLEAN_FALCON512_CLEAN_expand_privkey(fpr *expanded_key,
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const int8_t *f, const int8_t *g,
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const int8_t *F, const int8_t *G,
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unsigned logn, uint8_t *tmp) {
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size_t n;
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fpr *rf, *rg, *rF, *rG;
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fpr *b00, *b01, *b10, *b11;
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fpr *g00, *g01, *g11, *gxx;
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fpr *tree;
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n = MKN(logn);
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b00 = expanded_key + skoff_b00(logn);
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b01 = expanded_key + skoff_b01(logn);
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b10 = expanded_key + skoff_b10(logn);
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b11 = expanded_key + skoff_b11(logn);
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tree = expanded_key + skoff_tree(logn);
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/*
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* We load the private key elements directly into the B0 matrix,
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* since B0 = [[g, -f], [G, -F]].
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*/
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rf = b01;
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rg = b00;
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rF = b11;
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rG = b10;
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smallints_to_fpr(rf, f, logn);
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smallints_to_fpr(rg, g, logn);
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smallints_to_fpr(rF, F, logn);
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smallints_to_fpr(rG, G, logn);
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/*
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* Compute the FFT for the key elements, and negate f and F.
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*/
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PQCLEAN_FALCON512_CLEAN_FFT(rf, logn);
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PQCLEAN_FALCON512_CLEAN_FFT(rg, logn);
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PQCLEAN_FALCON512_CLEAN_FFT(rF, logn);
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PQCLEAN_FALCON512_CLEAN_FFT(rG, logn);
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PQCLEAN_FALCON512_CLEAN_poly_neg(rf, logn);
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PQCLEAN_FALCON512_CLEAN_poly_neg(rF, logn);
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/*
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* The Gram matrix is G = B·B*. Formulas are:
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* g00 = b00*adj(b00) + b01*adj(b01)
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* g01 = b00*adj(b10) + b01*adj(b11)
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* g10 = b10*adj(b00) + b11*adj(b01)
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* g11 = b10*adj(b10) + b11*adj(b11)
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*
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* For historical reasons, this implementation uses
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* g00, g01 and g11 (upper triangle).
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*/
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g00 = (fpr *)tmp;
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g01 = g00 + n;
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g11 = g01 + n;
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gxx = g11 + n;
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memcpy(g00, b00, n * sizeof * b00);
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PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(g00, logn);
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memcpy(gxx, b01, n * sizeof * b01);
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PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(gxx, logn);
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PQCLEAN_FALCON512_CLEAN_poly_add(g00, gxx, logn);
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memcpy(g01, b00, n * sizeof * b00);
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PQCLEAN_FALCON512_CLEAN_poly_muladj_fft(g01, b10, logn);
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memcpy(gxx, b01, n * sizeof * b01);
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PQCLEAN_FALCON512_CLEAN_poly_muladj_fft(gxx, b11, logn);
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PQCLEAN_FALCON512_CLEAN_poly_add(g01, gxx, logn);
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memcpy(g11, b10, n * sizeof * b10);
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PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(g11, logn);
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memcpy(gxx, b11, n * sizeof * b11);
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PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(gxx, logn);
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PQCLEAN_FALCON512_CLEAN_poly_add(g11, gxx, logn);
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/*
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* Compute the Falcon tree.
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*/
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ffLDL_fft(tree, g00, g01, g11, logn, gxx);
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/*
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* Normalize tree.
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*/
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ffLDL_binary_normalize(tree, logn);
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}
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typedef int (*samplerZ)(void *ctx, fpr mu, fpr sigma);
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/*
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* Perform Fast Fourier Sampling for target vector t. The Gram matrix
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* is provided (G = [[g00, g01], [adj(g01), g11]]). The sampled vector
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* is written over (t0,t1). The Gram matrix is modified as well. The
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* tmp[] buffer must have room for four polynomials.
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*/
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static void
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ffSampling_fft_dyntree(samplerZ samp, void *samp_ctx,
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fpr *t0, fpr *t1,
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fpr *g00, fpr *g01, fpr *g11,
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unsigned logn, fpr *tmp) {
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size_t n, hn;
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fpr *z0, *z1;
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/*
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* Deepest level: the LDL tree leaf value is just g00 (the
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* array has length only 1 at this point); we normalize it
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* with regards to sigma, then use it for sampling.
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*/
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if (logn == 0) {
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fpr leaf;
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leaf = g00[0];
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leaf = fpr_mul(fpr_sqrt(leaf), fpr_inv_sigma);
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t0[0] = fpr_of(samp(samp_ctx, t0[0], leaf));
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t1[0] = fpr_of(samp(samp_ctx, t1[0], leaf));
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return;
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}
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n = (size_t)1 << logn;
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hn = n >> 1;
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/*
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* Decompose G into LDL. We only need d00 (identical to g00),
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* d11, and l10; we do that in place.
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*/
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PQCLEAN_FALCON512_CLEAN_poly_LDL_fft(g00, g01, g11, logn);
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/*
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* Split d00 and d11 and expand them into half-size quasi-cyclic
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* Gram matrices. We also save l10 in tmp[].
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*/
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(tmp, tmp + hn, g00, logn);
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memcpy(g00, tmp, n * sizeof * tmp);
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(tmp, tmp + hn, g11, logn);
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memcpy(g11, tmp, n * sizeof * tmp);
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memcpy(tmp, g01, n * sizeof * g01);
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memcpy(g01, g00, hn * sizeof * g00);
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memcpy(g01 + hn, g11, hn * sizeof * g00);
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/*
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* The half-size Gram matrices for the recursive LDL tree
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* building are now:
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* - left sub-tree: g00, g00+hn, g01
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* - right sub-tree: g11, g11+hn, g01+hn
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* l10 is in tmp[].
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*/
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/*
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* We split t1 and use the first recursive call on the two
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* halves, using the right sub-tree. The result is merged
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* back into tmp + 2*n.
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*/
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z1 = tmp + n;
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(z1, z1 + hn, t1, logn);
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ffSampling_fft_dyntree(samp, samp_ctx, z1, z1 + hn,
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g11, g11 + hn, g01 + hn, logn - 1, z1 + n);
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PQCLEAN_FALCON512_CLEAN_poly_merge_fft(tmp + (n << 1), z1, z1 + hn, logn);
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/*
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* Compute tb0 = t0 + (t1 - z1) * l10.
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* At that point, l10 is in tmp, t1 is unmodified, and z1 is
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* in tmp + (n << 1). The buffer in z1 is free.
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*
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* In the end, z1 is written over t1, and tb0 is in t0.
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*/
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memcpy(z1, t1, n * sizeof * t1);
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PQCLEAN_FALCON512_CLEAN_poly_sub(z1, tmp + (n << 1), logn);
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memcpy(t1, tmp + (n << 1), n * sizeof * tmp);
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PQCLEAN_FALCON512_CLEAN_poly_mul_fft(tmp, z1, logn);
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PQCLEAN_FALCON512_CLEAN_poly_add(t0, tmp, logn);
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/*
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* Second recursive invocation, on the split tb0 (currently in t0)
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* and the left sub-tree.
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*/
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z0 = tmp;
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(z0, z0 + hn, t0, logn);
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ffSampling_fft_dyntree(samp, samp_ctx, z0, z0 + hn,
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g00, g00 + hn, g01, logn - 1, z0 + n);
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PQCLEAN_FALCON512_CLEAN_poly_merge_fft(t0, z0, z0 + hn, logn);
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}
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/*
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* Perform Fast Fourier Sampling for target vector t and LDL tree T.
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* tmp[] must have size for at least two polynomials of size 2^logn.
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*/
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static void
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ffSampling_fft(samplerZ samp, void *samp_ctx,
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fpr *z0, fpr *z1,
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const fpr *tree,
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const fpr *t0, const fpr *t1, unsigned logn,
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fpr *tmp) {
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size_t n, hn;
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const fpr *tree0, *tree1;
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n = (size_t)1 << logn;
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if (n == 1) {
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fpr x0, x1, sigma;
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x0 = t0[0];
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x1 = t1[0];
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sigma = tree[0];
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z0[0] = fpr_of(samp(samp_ctx, x0, sigma));
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z1[0] = fpr_of(samp(samp_ctx, x1, sigma));
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return;
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}
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hn = n >> 1;
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tree0 = tree + n;
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tree1 = tree + n + ffLDL_treesize(logn - 1);
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/*
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* We split t1 into z1 (reused as temporary storage), then do
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* the recursive invocation, with output in tmp. We finally
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* merge back into z1.
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*/
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(z1, z1 + hn, t1, logn);
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ffSampling_fft(samp, samp_ctx, tmp, tmp + hn,
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tree1, z1, z1 + hn, logn - 1, tmp + n);
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PQCLEAN_FALCON512_CLEAN_poly_merge_fft(z1, tmp, tmp + hn, logn);
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/*
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* Compute tb0 = t0 + (t1 - z1) * L. Value tb0 ends up in tmp[].
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*/
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memcpy(tmp, t1, n * sizeof * t1);
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PQCLEAN_FALCON512_CLEAN_poly_sub(tmp, z1, logn);
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PQCLEAN_FALCON512_CLEAN_poly_mul_fft(tmp, tree, logn);
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PQCLEAN_FALCON512_CLEAN_poly_add(tmp, t0, logn);
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/*
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* Second recursive invocation.
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*/
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PQCLEAN_FALCON512_CLEAN_poly_split_fft(z0, z0 + hn, tmp, logn);
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ffSampling_fft(samp, samp_ctx, tmp, tmp + hn,
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tree0, z0, z0 + hn, logn - 1, tmp + n);
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PQCLEAN_FALCON512_CLEAN_poly_merge_fft(z0, tmp, tmp + hn, logn);
|
|
}
|
|
|
|
/*
|
|
* Compute a signature: the signature contains two vectors, s1 and s2;
|
|
* the caller must still check that they comply with the signature
|
|
* bound, and try again if that is not the case. The s1 vector is not
|
|
* returned; instead, its squared norm (saturated) is returned. This
|
|
* function uses an expanded key.
|
|
*
|
|
* tmp[] must have room for at least six polynomials.
|
|
*/
|
|
static uint32_t
|
|
do_sign_tree(samplerZ samp, void *samp_ctx, int16_t *s2,
|
|
const fpr *expanded_key,
|
|
const uint16_t *hm,
|
|
unsigned logn, fpr *tmp) {
|
|
size_t n, u;
|
|
fpr *t0, *t1, *tx, *ty;
|
|
const fpr *b00, *b01, *b10, *b11, *tree;
|
|
fpr ni;
|
|
uint32_t sqn, ng;
|
|
|
|
n = MKN(logn);
|
|
t0 = tmp;
|
|
t1 = t0 + n;
|
|
b00 = expanded_key + skoff_b00(logn);
|
|
b01 = expanded_key + skoff_b01(logn);
|
|
b10 = expanded_key + skoff_b10(logn);
|
|
b11 = expanded_key + skoff_b11(logn);
|
|
tree = expanded_key + skoff_tree(logn);
|
|
|
|
/*
|
|
* Set the target vector to [hm, 0] (hm is the hashed message).
|
|
*/
|
|
for (u = 0; u < n; u ++) {
|
|
t0[u] = fpr_of(hm[u]);
|
|
/* This is implicit.
|
|
t1[u] = fpr_zero;
|
|
*/
|
|
}
|
|
|
|
/*
|
|
* Apply the lattice basis to obtain the real target
|
|
* vector (after normalization with regards to modulus).
|
|
*/
|
|
PQCLEAN_FALCON512_CLEAN_FFT(t0, logn);
|
|
ni = fpr_inverse_of_q;
|
|
memcpy(t1, t0, n * sizeof * t0);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(t1, b01, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulconst(t1, fpr_neg(ni), logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(t0, b11, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulconst(t0, ni, logn);
|
|
|
|
tx = t1 + n;
|
|
ty = tx + n;
|
|
|
|
/*
|
|
* Apply sampling. Output is written back in [tx, ty].
|
|
*/
|
|
ffSampling_fft(samp, samp_ctx, tx, ty, tree, t0, t1, logn, ty + n);
|
|
|
|
/*
|
|
* Get the lattice point corresponding to that tiny vector.
|
|
*/
|
|
memcpy(t0, tx, n * sizeof * tx);
|
|
memcpy(t1, ty, n * sizeof * ty);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(tx, b00, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(ty, b10, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(tx, ty, logn);
|
|
memcpy(ty, t0, n * sizeof * t0);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(ty, b01, logn);
|
|
|
|
memcpy(t0, tx, n * sizeof * tx);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(t1, b11, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(t1, ty, logn);
|
|
|
|
PQCLEAN_FALCON512_CLEAN_iFFT(t0, logn);
|
|
PQCLEAN_FALCON512_CLEAN_iFFT(t1, logn);
|
|
|
|
/*
|
|
* Compute the signature.
|
|
*/
|
|
sqn = 0;
|
|
ng = 0;
|
|
for (u = 0; u < n; u ++) {
|
|
int32_t z;
|
|
|
|
z = (int32_t)hm[u] - (int32_t)fpr_rint(t0[u]);
|
|
sqn += (uint32_t)(z * z);
|
|
ng |= sqn;
|
|
}
|
|
sqn |= -(ng >> 31);
|
|
for (u = 0; u < n; u ++) {
|
|
s2[u] = (int16_t) - fpr_rint(t1[u]);
|
|
}
|
|
return sqn;
|
|
}
|
|
|
|
/*
|
|
* Compute a signature: the signature contains two vectors, s1 and s2;
|
|
* the caller must still check that they comply with the signature
|
|
* bound, and try again if that is not the case. The s1 vector is not
|
|
* returned; instead, its squared norm (saturated) is returned. This
|
|
* function uses a raw key and recomputes the B0 matrix and LDL tree
|
|
* dynamically.
|
|
*
|
|
* tmp[] must have room for at least nine polynomials.
|
|
*/
|
|
static uint32_t
|
|
do_sign_dyn(samplerZ samp, void *samp_ctx, int16_t *s2,
|
|
const int8_t *f, const int8_t *g,
|
|
const int8_t *F, const int8_t *G,
|
|
const uint16_t *hm, unsigned logn, fpr *tmp) {
|
|
size_t n, u;
|
|
fpr *t0, *t1, *tx, *ty;
|
|
fpr *b00, *b01, *b10, *b11, *g00, *g01, *g11;
|
|
fpr ni;
|
|
uint32_t sqn, ng;
|
|
|
|
n = MKN(logn);
|
|
|
|
/*
|
|
* Lattice basis is B = [[g, -f], [G, -F]]. We convert it to FFT.
|
|
*/
|
|
b00 = tmp;
|
|
b01 = b00 + n;
|
|
b10 = b01 + n;
|
|
b11 = b10 + n;
|
|
smallints_to_fpr(b01, f, logn);
|
|
smallints_to_fpr(b00, g, logn);
|
|
smallints_to_fpr(b11, F, logn);
|
|
smallints_to_fpr(b10, G, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b01, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b00, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b11, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b10, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_neg(b01, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_neg(b11, logn);
|
|
|
|
/*
|
|
* Compute the Gram matrix G = B·B*. Formulas are:
|
|
* g00 = b00*adj(b00) + b01*adj(b01)
|
|
* g01 = b00*adj(b10) + b01*adj(b11)
|
|
* g10 = b10*adj(b00) + b11*adj(b01)
|
|
* g11 = b10*adj(b10) + b11*adj(b11)
|
|
*
|
|
* For historical reasons, this implementation uses
|
|
* g00, g01 and g11 (upper triangle). g10 is not kept
|
|
* since it is equal to adj(g01).
|
|
*
|
|
* We _replace_ the matrix B with the Gram matrix, but we
|
|
* must keep b01 and b11 for computing the target vector.
|
|
*/
|
|
t0 = b11 + n;
|
|
t1 = t0 + n;
|
|
|
|
memcpy(t0, b01, n * sizeof * b01);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(t0, logn); // t0 <- b01*adj(b01)
|
|
|
|
memcpy(t1, b00, n * sizeof * b00);
|
|
PQCLEAN_FALCON512_CLEAN_poly_muladj_fft(t1, b10, logn); // t1 <- b00*adj(b10)
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(b00, logn); // b00 <- b00*adj(b00)
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(b00, t0, logn); // b00 <- g00
|
|
memcpy(t0, b01, n * sizeof * b01);
|
|
PQCLEAN_FALCON512_CLEAN_poly_muladj_fft(b01, b11, logn); // b01 <- b01*adj(b11)
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(b01, t1, logn); // b01 <- g01
|
|
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(b10, logn); // b10 <- b10*adj(b10)
|
|
memcpy(t1, b11, n * sizeof * b11);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulselfadj_fft(t1, logn); // t1 <- b11*adj(b11)
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(b10, t1, logn); // b10 <- g11
|
|
|
|
/*
|
|
* We rename variables to make things clearer. The three elements
|
|
* of the Gram matrix uses the first 3*n slots of tmp[], followed
|
|
* by b11 and b01 (in that order).
|
|
*/
|
|
g00 = b00;
|
|
g01 = b01;
|
|
g11 = b10;
|
|
b01 = t0;
|
|
t0 = b01 + n;
|
|
t1 = t0 + n;
|
|
|
|
/*
|
|
* Memory layout at that point:
|
|
* g00 g01 g11 b11 b01 t0 t1
|
|
*/
|
|
|
|
/*
|
|
* Set the target vector to [hm, 0] (hm is the hashed message).
|
|
*/
|
|
for (u = 0; u < n; u ++) {
|
|
t0[u] = fpr_of(hm[u]);
|
|
/* This is implicit.
|
|
t1[u] = fpr_zero;
|
|
*/
|
|
}
|
|
|
|
/*
|
|
* Apply the lattice basis to obtain the real target
|
|
* vector (after normalization with regards to modulus).
|
|
*/
|
|
PQCLEAN_FALCON512_CLEAN_FFT(t0, logn);
|
|
ni = fpr_inverse_of_q;
|
|
memcpy(t1, t0, n * sizeof * t0);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(t1, b01, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulconst(t1, fpr_neg(ni), logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(t0, b11, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mulconst(t0, ni, logn);
|
|
|
|
/*
|
|
* b01 and b11 can be discarded, so we move back (t0,t1).
|
|
* Memory layout is now:
|
|
* g00 g01 g11 t0 t1
|
|
*/
|
|
memcpy(b11, t0, n * 2 * sizeof * t0);
|
|
t0 = g11 + n;
|
|
t1 = t0 + n;
|
|
|
|
/*
|
|
* Apply sampling; result is written over (t0,t1).
|
|
*/
|
|
ffSampling_fft_dyntree(samp, samp_ctx,
|
|
t0, t1, g00, g01, g11, logn, t1 + n);
|
|
|
|
/*
|
|
* We arrange the layout back to:
|
|
* b00 b01 b10 b11 t0 t1
|
|
*
|
|
* We did not conserve the matrix basis, so we must recompute
|
|
* it now.
|
|
*/
|
|
b00 = tmp;
|
|
b01 = b00 + n;
|
|
b10 = b01 + n;
|
|
b11 = b10 + n;
|
|
memmove(b11 + n, t0, n * 2 * sizeof * t0);
|
|
t0 = b11 + n;
|
|
t1 = t0 + n;
|
|
smallints_to_fpr(b01, f, logn);
|
|
smallints_to_fpr(b00, g, logn);
|
|
smallints_to_fpr(b11, F, logn);
|
|
smallints_to_fpr(b10, G, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b01, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b00, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b11, logn);
|
|
PQCLEAN_FALCON512_CLEAN_FFT(b10, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_neg(b01, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_neg(b11, logn);
|
|
tx = t1 + n;
|
|
ty = tx + n;
|
|
|
|
/*
|
|
* Get the lattice point corresponding to that tiny vector.
|
|
*/
|
|
memcpy(tx, t0, n * sizeof * t0);
|
|
memcpy(ty, t1, n * sizeof * t1);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(tx, b00, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(ty, b10, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(tx, ty, logn);
|
|
memcpy(ty, t0, n * sizeof * t0);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(ty, b01, logn);
|
|
|
|
memcpy(t0, tx, n * sizeof * tx);
|
|
PQCLEAN_FALCON512_CLEAN_poly_mul_fft(t1, b11, logn);
|
|
PQCLEAN_FALCON512_CLEAN_poly_add(t1, ty, logn);
|
|
PQCLEAN_FALCON512_CLEAN_iFFT(t0, logn);
|
|
PQCLEAN_FALCON512_CLEAN_iFFT(t1, logn);
|
|
|
|
sqn = 0;
|
|
ng = 0;
|
|
for (u = 0; u < n; u ++) {
|
|
int32_t z;
|
|
|
|
z = (int32_t)hm[u] - (int32_t)fpr_rint(t0[u]);
|
|
sqn += (uint32_t)(z * z);
|
|
ng |= sqn;
|
|
}
|
|
sqn |= -(ng >> 31);
|
|
for (u = 0; u < n; u ++) {
|
|
s2[u] = (int16_t) - fpr_rint(t1[u]);
|
|
}
|
|
return sqn;
|
|
}
|
|
|
|
/*
|
|
* Sample an integer value along a half-gaussian distribution centered
|
|
* on zero and standard deviation 1.8205, with a precision of 72 bits.
|
|
*/
|
|
static int
|
|
gaussian0_sampler(prng *p) {
|
|
|
|
static const uint32_t dist[] = {
|
|
6031371U, 13708371U, 13035518U,
|
|
5186761U, 1487980U, 12270720U,
|
|
3298653U, 4688887U, 5511555U,
|
|
1551448U, 9247616U, 9467675U,
|
|
539632U, 14076116U, 5909365U,
|
|
138809U, 10836485U, 13263376U,
|
|
26405U, 15335617U, 16601723U,
|
|
3714U, 14514117U, 13240074U,
|
|
386U, 8324059U, 3276722U,
|
|
29U, 12376792U, 7821247U,
|
|
1U, 11611789U, 3398254U,
|
|
0U, 1194629U, 4532444U,
|
|
0U, 37177U, 2973575U,
|
|
0U, 855U, 10369757U,
|
|
0U, 14U, 9441597U,
|
|
0U, 0U, 3075302U,
|
|
0U, 0U, 28626U,
|
|
0U, 0U, 197U,
|
|
0U, 0U, 1U
|
|
};
|
|
|
|
uint32_t v0, v1, v2, hi;
|
|
uint64_t lo;
|
|
size_t u;
|
|
int z;
|
|
|
|
/*
|
|
* Get a random 72-bit value, into three 24-bit limbs v0..v2.
|
|
*/
|
|
lo = prng_get_u64(p);
|
|
hi = prng_get_u8(p);
|
|
v0 = (uint32_t)lo & 0xFFFFFF;
|
|
v1 = (uint32_t)(lo >> 24) & 0xFFFFFF;
|
|
v2 = (uint32_t)(lo >> 48) | (hi << 16);
|
|
|
|
/*
|
|
* Sampled value is z, such that v0..v2 is lower than the first
|
|
* z elements of the table.
|
|
*/
|
|
z = 0;
|
|
for (u = 0; u < (sizeof dist) / sizeof(dist[0]); u += 3) {
|
|
uint32_t w0, w1, w2, cc;
|
|
|
|
w0 = dist[u + 2];
|
|
w1 = dist[u + 1];
|
|
w2 = dist[u + 0];
|
|
cc = (v0 - w0) >> 31;
|
|
cc = (v1 - w1 - cc) >> 31;
|
|
cc = (v2 - w2 - cc) >> 31;
|
|
z += (int)cc;
|
|
}
|
|
return z;
|
|
|
|
}
|
|
|
|
/*
|
|
* Sample a bit with probability exp(-x) for some x >= 0.
|
|
*/
|
|
static int
|
|
BerExp(prng *p, fpr x) {
|
|
int s, i;
|
|
fpr r;
|
|
uint32_t sw, w;
|
|
uint64_t z;
|
|
|
|
/*
|
|
* Reduce x modulo log(2): x = s*log(2) + r, with s an integer,
|
|
* and 0 <= r < log(2). Since x >= 0, we can use fpr_trunc().
|
|
*/
|
|
s = (int)fpr_trunc(fpr_mul(x, fpr_inv_log2));
|
|
r = fpr_sub(x, fpr_mul(fpr_of(s), fpr_log2));
|
|
|
|
/*
|
|
* It may happen (quite rarely) that s >= 64; if sigma = 1.2
|
|
* (the minimum value for sigma), r = 0 and b = 1, then we get
|
|
* s >= 64 if the half-Gaussian produced a z >= 13, which happens
|
|
* with probability about 0.000000000230383991, which is
|
|
* approximatively equal to 2^(-32). In any case, if s >= 64,
|
|
* then BerExp will be non-zero with probability less than
|
|
* 2^(-64), so we can simply saturate s at 63.
|
|
*/
|
|
sw = (uint32_t)s;
|
|
sw ^= (sw ^ 63) & -((63 - sw) >> 31);
|
|
s = (int)sw;
|
|
|
|
/*
|
|
* Compute exp(-r); we know that 0 <= r < log(2) at this point, so
|
|
* we can use fpr_expm_p63(), which yields a result scaled to 2^63.
|
|
* We scale it up to 2^64, then right-shift it by s bits because
|
|
* we really want exp(-x) = 2^(-s)*exp(-r).
|
|
*
|
|
* The "-1" operation makes sure that the value fits on 64 bits
|
|
* (i.e. if r = 0, we may get 2^64, and we prefer 2^64-1 in that
|
|
* case). The bias is negligible since fpr_expm_p63() only computes
|
|
* with 51 bits of precision or so.
|
|
*/
|
|
z = ((fpr_expm_p63(r) << 1) - 1) >> s;
|
|
|
|
/*
|
|
* Sample a bit with probability exp(-x). Since x = s*log(2) + r,
|
|
* exp(-x) = 2^-s * exp(-r), we compare lazily exp(-x) with the
|
|
* PRNG output to limit its consumption, the sign of the difference
|
|
* yields the expected result.
|
|
*/
|
|
i = 64;
|
|
do {
|
|
i -= 8;
|
|
w = prng_get_u8(p) - ((uint32_t)(z >> i) & 0xFF);
|
|
} while (!w && i > 0);
|
|
return (int)(w >> 31);
|
|
}
|
|
|
|
typedef struct {
|
|
prng p;
|
|
fpr sigma_min;
|
|
} sampler_context;
|
|
|
|
/*
|
|
* The sampler produces a random integer that follows a discrete Gaussian
|
|
* distribution, centered on mu, and with standard deviation sigma. The
|
|
* provided parameter isigma is equal to 1/sigma.
|
|
*
|
|
* The value of sigma MUST lie between 1 and 2 (i.e. isigma lies between
|
|
* 0.5 and 1); in Falcon, sigma should always be between 1.2 and 1.9.
|
|
*/
|
|
static int
|
|
sampler(void *ctx, fpr mu, fpr isigma) {
|
|
sampler_context *spc;
|
|
int s;
|
|
fpr r, dss, ccs;
|
|
|
|
spc = ctx;
|
|
|
|
/*
|
|
* Center is mu. We compute mu = s + r where s is an integer
|
|
* and 0 <= r < 1.
|
|
*/
|
|
s = (int)fpr_floor(mu);
|
|
r = fpr_sub(mu, fpr_of(s));
|
|
|
|
/*
|
|
* dss = 1/(2*sigma^2) = 0.5*(isigma^2).
|
|
*/
|
|
dss = fpr_half(fpr_sqr(isigma));
|
|
|
|
/*
|
|
* ccs = sigma_min / sigma = sigma_min * isigma.
|
|
*/
|
|
ccs = fpr_mul(isigma, spc->sigma_min);
|
|
|
|
/*
|
|
* We now need to sample on center r.
|
|
*/
|
|
for (;;) {
|
|
int z0, z, b;
|
|
fpr x;
|
|
|
|
/*
|
|
* Sample z for a Gaussian distribution. Then get a
|
|
* random bit b to turn the sampling into a bimodal
|
|
* distribution: if b = 1, we use z+1, otherwise we
|
|
* use -z. We thus have two situations:
|
|
*
|
|
* - b = 1: z >= 1 and sampled against a Gaussian
|
|
* centered on 1.
|
|
* - b = 0: z <= 0 and sampled against a Gaussian
|
|
* centered on 0.
|
|
*/
|
|
z0 = gaussian0_sampler(&spc->p);
|
|
b = prng_get_u8(&spc->p) & 1;
|
|
z = b + ((b << 1) - 1) * z0;
|
|
|
|
/*
|
|
* Rejection sampling. We want a Gaussian centered on r;
|
|
* but we sampled against a Gaussian centered on b (0 or
|
|
* 1). But we know that z is always in the range where
|
|
* our sampling distribution is greater than the Gaussian
|
|
* distribution, so rejection works.
|
|
*
|
|
* We got z with distribution:
|
|
* G(z) = exp(-((z-b)^2)/(2*sigma0^2))
|
|
* We target distribution:
|
|
* S(z) = exp(-((z-r)^2)/(2*sigma^2))
|
|
* Rejection sampling works by keeping the value z with
|
|
* probability S(z)/G(z), and starting again otherwise.
|
|
* This requires S(z) <= G(z), which is the case here.
|
|
* Thus, we simply need to keep our z with probability:
|
|
* P = exp(-x)
|
|
* where:
|
|
* x = ((z-r)^2)/(2*sigma^2) - ((z-b)^2)/(2*sigma0^2)
|
|
*
|
|
* Here, we scale up the Bernouilli distribution, which
|
|
* makes rejection more probable, but makes rejection
|
|
* rate sufficiently decorrelated from the Gaussian
|
|
* center and standard deviation that the whole sampler
|
|
* can be said to be constant-time.
|
|
*/
|
|
x = fpr_mul(fpr_sqr(fpr_sub(fpr_of(z), r)), dss);
|
|
x = fpr_sub(x, fpr_mul(fpr_of(z0 * z0), fpr_inv_2sqrsigma0));
|
|
x = fpr_mul(x, ccs);
|
|
if (BerExp(&spc->p, x)) {
|
|
/*
|
|
* Rejection sampling was centered on r, but the
|
|
* actual center is mu = s + r.
|
|
*/
|
|
return s + z;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* see inner.h */
|
|
void
|
|
PQCLEAN_FALCON512_CLEAN_sign_tree(int16_t *sig, shake256_context *rng,
|
|
const fpr *expanded_key,
|
|
const uint16_t *hm, unsigned logn, uint8_t *tmp) {
|
|
fpr *ftmp;
|
|
|
|
ftmp = (fpr *)tmp;
|
|
for (;;) {
|
|
/*
|
|
* Signature produces short vectors s1 and s2. The
|
|
* signature is acceptable only if the aggregate vector
|
|
* s1,s2 is short; we must use the same bound as the
|
|
* verifier.
|
|
*
|
|
* If the signature is acceptable, then we return only s2
|
|
* (the verifier recomputes s1 from s2, the hashed message,
|
|
* and the public key).
|
|
*/
|
|
sampler_context spc;
|
|
samplerZ samp;
|
|
void *samp_ctx;
|
|
uint32_t sqn;
|
|
|
|
/*
|
|
* Normal sampling. We use a fast PRNG seeded from our
|
|
* SHAKE context ('rng').
|
|
*/
|
|
spc.sigma_min = (logn == 10)
|
|
? fpr_sigma_min_10
|
|
: fpr_sigma_min_9;
|
|
PQCLEAN_FALCON512_CLEAN_prng_init(&spc.p, rng);
|
|
samp = sampler;
|
|
samp_ctx = &spc;
|
|
|
|
/*
|
|
* Do the actual signature.
|
|
*/
|
|
sqn = do_sign_tree(samp, samp_ctx, sig,
|
|
expanded_key, hm, logn, ftmp);
|
|
|
|
/*
|
|
* Check that the norm is correct. With our chosen
|
|
* acceptance bound, this should almost always be true.
|
|
* With a tighter bound, it may happen sometimes that we
|
|
* end up with an invalidly large signature, in which
|
|
* case we just loop.
|
|
*/
|
|
if (PQCLEAN_FALCON512_CLEAN_is_short_half(sqn, sig, logn)) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* see inner.h */
|
|
void
|
|
PQCLEAN_FALCON512_CLEAN_sign_dyn(int16_t *sig, shake256_context *rng,
|
|
const int8_t *f, const int8_t *g,
|
|
const int8_t *F, const int8_t *G,
|
|
const uint16_t *hm, unsigned logn, uint8_t *tmp) {
|
|
fpr *ftmp;
|
|
|
|
ftmp = (fpr *)tmp;
|
|
for (;;) {
|
|
/*
|
|
* Signature produces short vectors s1 and s2. The
|
|
* signature is acceptable only if the aggregate vector
|
|
* s1,s2 is short; we must use the same bound as the
|
|
* verifier.
|
|
*
|
|
* If the signature is acceptable, then we return only s2
|
|
* (the verifier recomputes s1 from s2, the hashed message,
|
|
* and the public key).
|
|
*/
|
|
sampler_context spc;
|
|
samplerZ samp;
|
|
void *samp_ctx;
|
|
uint32_t sqn;
|
|
|
|
/*
|
|
* Normal sampling. We use a fast PRNG seeded from our
|
|
* SHAKE context ('rng').
|
|
*/
|
|
spc.sigma_min = (logn == 10)
|
|
? fpr_sigma_min_10
|
|
: fpr_sigma_min_9;
|
|
PQCLEAN_FALCON512_CLEAN_prng_init(&spc.p, rng);
|
|
samp = sampler;
|
|
samp_ctx = &spc;
|
|
|
|
/*
|
|
* Do the actual signature.
|
|
*/
|
|
sqn = do_sign_dyn(samp, samp_ctx, sig,
|
|
f, g, F, G, hm, logn, ftmp);
|
|
|
|
/*
|
|
* Check that the norm is correct. With our chosen
|
|
* acceptance bound, this should almost always be true.
|
|
* With a tighter bound, it may happen sometimes that we
|
|
* end up with an invalidly large signature, in which
|
|
* case we just loop.
|
|
*/
|
|
if (PQCLEAN_FALCON512_CLEAN_is_short_half(sqn, sig, logn)) {
|
|
break;
|
|
}
|
|
}
|
|
}
|