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Handle more values in mp_exptmod

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Handle prime (modulus) of 0 and 1.
Handle exponent of 0.
Fix for base of 0 in fp_exptmod and hadnle base of 0 in mp_exptmod.
fp_exptmod - Don't modify X's sign during operation when passed in as negative.
This commit is contained in:
Sean Parkinson 2019-12-04 09:08:04 +10:00
parent 7e45ae2ec6
commit c5f9a601e8
2 changed files with 29 additions and 12 deletions
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14
wolfcrypt/src/integer.c
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@ -843,9 +843,21 @@ int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
int dr;
/* modulus P must be positive */
if (P->sign == MP_NEG) {
if (mp_iszero(P) || P->sign == MP_NEG) {
return MP_VAL;
}
if (mp_isone(P)) {
mp_set(Y, 0);
return MP_OKAY;
}
if (mp_iszero(X)) {
mp_set(Y, 1);
return MP_OKAY;
}
if (mp_iszero(G)) {
mp_set(Y, 0);
return MP_OKAY;
}
/* if exponent X is negative we have to recurse */
if (X->sign == MP_NEG) {

27
wolfcrypt/src/tfm.c
View File

@ -2183,14 +2183,21 @@ int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
int x = fp_count_bits (X);
#endif
if (fp_iszero(G)) {
fp_set(G, 0);
/* handle modulus of zero and prevent overflows */
if (fp_iszero(P) || (P->used > (FP_SIZE/2))) {
return FP_VAL;
}
if (fp_isone(P)) {
fp_set(Y, 0);
return FP_OKAY;
}
/* prevent overflows */
if (P->used > (FP_SIZE/2)) {
return FP_VAL;
if (fp_iszero(X)) {
fp_set(Y, 1);
return FP_OKAY;
}
if (fp_iszero(G)) {
fp_set(Y, 0);
return FP_OKAY;
}
#if defined(WOLFSSL_ESP32WROOM32_CRYPT_RSA_PRI) && \
@ -2221,11 +2228,9 @@ int fp_exptmod(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
tmp[1].sign = FP_ZPOS;
err = fp_invmod(&tmp[0], &tmp[1], &tmp[0]);
if (err == FP_OKAY) {
X->sign = FP_ZPOS;
err = _fp_exptmod(&tmp[0], X, X->used, P, Y);
if (X != Y) {
X->sign = FP_NEG;
}
fp_copy(X, &tmp[1]);
tmp[1].sign = FP_ZPOS;
err = _fp_exptmod(&tmp[0], &tmp[1], tmp[1].used, P, Y);
if (P->sign == FP_NEG) {
fp_add(Y, P, Y);
}