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* cipher/random.c (mix_pool): Store the first hash at the end of the pool. -- This fixes a long standing bug (since 1998) in Libgcrypt and GnuPG. An attacker who obtains 580 bytes of the random number from the standard RNG can trivially predict the next 20 bytes of output. This bug does not affect the default generation of keys because running gpg for key creation creates at most 2 keys from the pool: For a single 4096 bit RSA key 512 byte of random are required and thus for the second key (encryption subkey), 20 bytes could be predicted from the the first key. However, the security of an OpenPGP key depends on the primary key (which was generated first) and thus the 20 predictable bytes should not be a problem. For the default key length of 2048 bit nothing will be predictable. For the former default of DSA+Elgamal key it is complicate to give an answer: For 2048 bit keys a pool of 30 non-secret candidate primes of about 300 bits each are first created. This reads at least 1140 bytes from the pool and thus parts could be predicted. At some point a 256 bit secret is read from the pool; which in the worst case might be partly predictable. The bug was found and reported by Felix Dörre and Vladimir Klebanov, Karlsruhe Institute of Technology. A paper describing the problem in detail will shortly be published. CVE-id: CVE-2016-6313 Signed-off-by: Werner Koch <wk@gnupg.org>