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ECDSA FP ECC: fix corner case

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When the same table is used for both base point and public point (which
is not a valid thing to do) then a corner case occurs when the table
point can be added to the same point. This has to be a double operation
instead.
The table point isn't able to be doubled as it has a z-ordinate of 0 and
the original point is overwritten with the invalid add result.
Fix this case by:
 - copying the table point into the result,
 - setting z-ordinate to Montgomery form of 1,
 - double the result point in place.
This commit is contained in:
Sean Parkinson
2021-05-28 12:57:16 +10:00
parent 1fe445368c
commit c69665b999
1 changed files with 12 additions and 1 deletions
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13
wolfcrypt/src/ecc.c
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@ -5942,7 +5942,18 @@ int ecc_projective_add_point_safe(ecc_point* A, ecc_point* B, ecc_point* R,
if ((err == MP_OKAY) && mp_iszero(R->z)) {
/* When all zero then should have done a double */
if (mp_iszero(R->x) && mp_iszero(R->y)) {
err = ecc_projective_dbl_point(B, R, a, modulus, mp);
if (mp_iszero(B->z)) {
err = wc_ecc_copy_point(B, R);
if (err == MP_OKAY) {
err = mp_montgomery_calc_normalization(R->z, modulus);
}
if (err == MP_OKAY) {
err = ecc_projective_dbl_point(R, R, a, modulus, mp);
}
}
else {
err = ecc_projective_dbl_point(B, R, a, modulus, mp);
}
}
/* When only Z zero then result is infinity */
else {