-rw-r--r-- 1592 libmceliece-20240726/crypto_kem/348864/vec/sk_gen.c raw
/*
This file is for secret-key generation
*/
// 20221230 djb: add linker lines
// linker define genpoly_gen
// linker use gf_iszero gf_mul gf_inv GF_mul
#include "sk_gen.h"
#include "randombytes.h"
#include "controlbits.h"
#include "params.h"
#include "util.h"
#include "gf.h"
#include "crypto_declassify.h"
#include "crypto_uint16.h"
static inline crypto_uint16 gf_is_zero_declassify(gf t)
{
crypto_uint16 mask = crypto_uint16_zero_mask(t);
crypto_declassify(&mask,sizeof mask);
return mask;
}
/* input: f, element in GF((2^m)^t) */
/* output: out, minimal polynomial of f */
/* return: 0 for success and -1 for failure */
int genpoly_gen(gf *out, gf *f)
{
int i, j, k, c;
gf mat[ SYS_T+1 ][ SYS_T ];
gf mask, inv, t;
// fill matrix
mat[0][0] = 1;
for (i = 1; i < SYS_T; i++)
mat[0][i] = 0;
for (i = 0; i < SYS_T; i++)
mat[1][i] = f[i];
for (j = 2; j <= SYS_T; j++)
GF_mul(mat[j], mat[j-1], f);
// gaussian
for (j = 0; j < SYS_T; j++)
{
for (k = j + 1; k < SYS_T; k++)
{
mask = gf_iszero(mat[ j ][ j ]);
for (c = j; c < SYS_T + 1; c++)
mat[ c ][ j ] ^= mat[ c ][ k ] & mask;
}
if ( gf_is_zero_declassify(mat[ j ][ j ]) ) // return if not systematic
{
return -1;
}
inv = gf_inv(mat[j][j]);
for (c = j; c < SYS_T + 1; c++)
mat[ c ][ j ] = gf_mul(mat[ c ][ j ], inv) ;
for (k = 0; k < SYS_T; k++)
{
if (k != j)
{
t = mat[ j ][ k ];
for (c = j; c < SYS_T + 1; c++)
mat[ c ][ k ] ^= gf_mul(mat[ c ][ j ], t);
}
}
}
for (i = 0; i < SYS_T; i++)
out[i] = mat[ SYS_T ][ i ];
return 0;
}