libgcrypt20 - security update

Felix Doerre and Vladimir Klebanov from the Karlsruhe Institute of
Technology discovered a flaw in the mixing functions of Libgcrypt’s
random number generator. An attacker who obtains 4640 bits from the RNG
can trivially predict the next 160 bits of output.

A first analysis on the impact of this bug for GnuPG shows that existing
RSA keys are not weakened. For DSA and Elgamal keys it is also unlikely
that the private key can be predicted from other public information.

For the stable distribution (jessie), this problem has been fixed in
version 1.6.3-2+deb8u2.

We recommend that you upgrade your libgcrypt20 packages.