cipher: Normalize the MPIs used as input to secret key functions.
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Description

cipher: Normalize the MPIs used as input to secret key functions.

* cipher/dsa.c (sign): Normalize INPUT.
* cipher/elgamal.c (decrypt): Normalize A and B.
* cipher/rsa.c (secret): Normalize the INPUT.
(rsa_decrypt): Reduce DATA before passing to secret.

mpi_normalize is in general not required because extra leading zeroes
do not harm the computation. However, adding extra all zero limbs or
padding with multiples of N may be useful in side-channel attacks.
This is an extra pre-caution in case RSA blinding has been disabled.

CVE-id: CVE-2013-4576