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Handle corner-cases of invmod() 

This fixes #67
This commit is contained in:
Steffen Jaeckel 2017-10-14 20:21:48 +02:00
parent 6fa127b707
commit 8dbfaff04e
2 changed files with 9 additions and 3 deletions
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6
bn_fast_mp_invmod.c
View File

@ -46,6 +46,12 @@ int fast_mp_invmod(const mp_int *a, const mp_int *b, mp_int *c)
goto LBL_ERR;
}
/* if one of x,y is zero return an error! */
if ((mp_iszero(&x) == MP_YES) || (mp_iszero(&y) == MP_YES)) {
res = MP_VAL;
goto LBL_ERR;
}
/* 3. u=x, v=y, A=1, B=0, C=0,D=1 */
if ((res = mp_copy(&x, &u)) != MP_OKAY) {
goto LBL_ERR;

6
bn_mp_invmod.c
View File

@ -18,14 +18,14 @@
/* hac 14.61, pp608 */
int mp_invmod(const mp_int *a, const mp_int *b, mp_int *c)
{
/* b cannot be negative */
if ((b->sign == MP_NEG) || (mp_iszero(b) == MP_YES)) {
/* b cannot be negative and has to be >1 */
if ((b->sign == MP_NEG) || (mp_cmp_d(b, 1) != MP_GT)) {
return MP_VAL;
}
#ifdef BN_FAST_MP_INVMOD_C
/* if the modulus is odd we can use a faster routine instead */
if ((mp_isodd(b) == MP_YES) && (mp_cmp_d(b, 1) != MP_EQ)) {
if ((mp_isodd(b) == MP_YES)) {
return fast_mp_invmod(a, b, c);
}
#endif