rsa, elgamal: avoid logical not operator in constant-time code
* cipher/elgamal.c (elg_decrypt): Replace ! operator with calls to ct_is_not_zero/ct_is_zero/ct_ulong_select. * cipher/rsa-common.c (_gcry_rsa_pkcs1_decode_for_enc): Replace ! operator with call to ct_is_zero. * cipher/rsa.c (rsa_decrypt): Replace ! operator with calls to ct_is_not_zero/ct_is_zero/ct_ulong_select. * src/const-time.c (_gcry_ct_vzero, _gcry_ct_vone): New. * src/const-time.h (_gcry_ct_vzero, _gcry_ct_vone): New. (ct_is_not_zero, ct_is_zero, DEFINE_CT_TYPE_SELECT_FUNC) (ct_uintptr_select, ct_ulong_select): New. (sexp_null_cond): Use ct_uintptr_select.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>