84 lines
1.6 KiB
C
84 lines
1.6 KiB
C
/*
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This file is for the Berlekamp-Massey algorithm
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see http://crypto.stanford.edu/~mironov/cs359/massey.pdf
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*/
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#include "bm.h"
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#include "params.h"
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#define min(a, b) (((a) < (b)) ? (a) : (b))
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/* the Berlekamp-Massey algorithm */
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/* input: s, sequence of field elements */
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/* output: out, minimal polynomial of s */
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void PQCLEAN_MCELIECE8192128_CLEAN_bm(gf *out, gf *s) {
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int i;
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uint16_t N = 0;
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uint16_t L = 0;
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uint16_t mle;
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uint16_t mne;
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gf T[ SYS_T + 1 ];
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gf C[ SYS_T + 1 ];
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gf B[ SYS_T + 1 ];
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gf b = 1, d, f;
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//
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for (i = 0; i < SYS_T + 1; i++) {
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C[i] = B[i] = 0;
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}
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B[1] = C[0] = 1;
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//
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for (N = 0; N < 2 * SYS_T; N++) {
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d = 0;
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for (i = 0; i <= min(N, SYS_T); i++) {
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d ^= PQCLEAN_MCELIECE8192128_CLEAN_gf_mul(C[i], s[ N - i]);
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}
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mne = d;
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mne -= 1;
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mne >>= 15;
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mne -= 1;
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mle = N;
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mle -= 2 * L;
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mle >>= 15;
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mle -= 1;
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mle &= mne;
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for (i = 0; i <= SYS_T; i++) {
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T[i] = C[i];
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}
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f = PQCLEAN_MCELIECE8192128_CLEAN_gf_frac(b, d);
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for (i = 0; i <= SYS_T; i++) {
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C[i] ^= PQCLEAN_MCELIECE8192128_CLEAN_gf_mul(f, B[i]) & mne;
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}
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L = (L & ~mle) | ((N + 1 - L) & mle);
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for (i = 0; i <= SYS_T; i++) {
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B[i] = (B[i] & ~mle) | (T[i] & mle);
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}
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b = (b & ~mle) | (d & mle);
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for (i = SYS_T; i >= 1; i--) {
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B[i] = B[i - 1];
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}
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B[0] = 0;
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}
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for (i = 0; i <= SYS_T; i++) {
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out[i] = C[ SYS_T - i ];
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}
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}
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