* cipher/elgamal.c (USE_BLINDING): New.
(decrypt): Rewrite to use ciphertext blinding.
--
CVE-id: CVE-2014-3591
As a countermeasure to a new side-channel attacks on sliding windows
exponentiation we blind the ciphertext for Elgamal decryption. This
is similar to what we are doing with RSA.
Unfortunately, the performance impact of Elgamal blinding is quite
noticeable: For a 3072 bit Elgamal key the decryption used to take
13ms; with the blinding it takes 24ms. This has been measured using
time(1), calling gpg with a 100 byte message, and having gpg modified
to run the pubkey_decrypt function 100 times and finally scale the
result (using an i5-2410M CPU @ 2.30GHz TP 220).
* cipher/rsa.c (secret): Normalize the INPUT.
(rsa_decrypt): Pass reduced data to secret.
* cipher/elgamal.c (decrypt): Normalize A and B.
* cipher/dsa.c (sign): Normalize HASH.
--
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. In
particular they are used by the acoustic crypt-analysis. This is an
extra pre-caution which alone would not be sufficient to mitigate the
described attack.
CVE-id: CVE-2013-4576
Signed-off-by: Werner Koch <wk@gnupg.org>
rijndael.c, rndunix.c, sha256.c, cast5.c, idea-stub.c, rmd160.c, rndw32.c,
sha512.c, md5.c, rmd160test.c, rsa.c, tiger.c: Edit all preprocessor
instructions to remove whitespace before the '#'. This is not required by
C89, but there are some compilers out there that don't like it.
