* src/Makefile.am (libgcrypt_la_SOURCES): Add const-time.h and
const-time.c.
* src/const-time.h (ct_not_equal_byte, sexp_null_cond): New.
(ct_memequal): New from NetBSD, modified return type and name.
* src/const-time.c: New.
* cipher/rsa-common.c (_gcry_rsa_pkcs1_decode_for_enc): Examine whole
sequence of the byte-array.  Use N0 to find the separator position, with
ct_not_equal_byte.  Return the MPI even when the case of an error.
* cipher/rsa-common.c (_gcry_rsa_oaep_decode): Use ct_memequal to
check LHASH.  Examine all the sequence of the byte-array.  Use N1 to
find the separator of 0x01.  Return the MPI even when the case of an
error.
* cipher/rsa.c (rsa_decrypt): Always build a SEXP.