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Heap Math exptmod: fixes for valid modulus checks

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mp_exptmod_base_2() uses Montogmery method and does not support even
modulus. Added check.
mp_exptmod_fast() uses Montogmery method when odd not when dr > 0.
Comment updated at call.
Reduce value of zero doesn't work for mp_reduece_2k. Changed setup of
use to check for zero and won't use it. Other methods won't work either.
This commit is contained in:
Sean Parkinson
2023-07-12 09:20:11 +10:00
parent d6a6cbb83e
commit b18bc86ef8
1 changed files with 6 additions and 4 deletions
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8
wolfcrypt/src/integer.c
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@@ -955,7 +955,7 @@ int wolfcrypt_mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
} }
#ifdef BN_MP_EXPTMOD_BASE_2 #ifdef BN_MP_EXPTMOD_BASE_2
if (G->used == 1 && G->dp[0] == 2) { if (G->used == 1 && G->dp[0] == 2 && mp_isodd(P) == MP_YES) {
return mp_exptmod_base_2(X, P, Y); return mp_exptmod_base_2(X, P, Y);
} }
#endif #endif
@@ -985,7 +985,7 @@ int wolfcrypt_mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
} }
#endif #endif
/* if the modulus is odd or dr != 0 use the montgomery method */ /* if the modulus is odd use the montgomery method, or use other known */
#ifdef BN_MP_EXPTMOD_FAST_C #ifdef BN_MP_EXPTMOD_FAST_C
if (mp_isodd (P) == MP_YES || dr != 0) { if (mp_isodd (P) == MP_YES || dr != 0) {
return mp_exptmod_fast (G, X, P, Y, dr); return mp_exptmod_fast (G, X, P, Y, dr);
@@ -1985,7 +1985,6 @@ int mp_dr_is_modulus(mp_int *a)
return 1; return 1;
} }
/* computes Y == G**X mod P, HAC pp.616, Algorithm 14.85 /* computes Y == G**X mod P, HAC pp.616, Algorithm 14.85
* *
* Uses a left-to-right k-ary sliding window to compute the modular * Uses a left-to-right k-ary sliding window to compute the modular
@@ -2113,7 +2112,10 @@ int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y,
if ((err = mp_reduce_2k_setup(P, &mp)) != MP_OKAY) { if ((err = mp_reduce_2k_setup(P, &mp)) != MP_OKAY) {
goto LBL_M; goto LBL_M;
} }
/* mp of zero is not usable */
if (mp != 0) {
redux = mp_reduce_2k; redux = mp_reduce_2k;
}
#endif #endif
} }