random: make backtracking attacks harder
At each extraction, we change (poolbits / 16) + 32 bits in the pool, or 96 bits in the case of the secondary pools. Thus, a brute-force backtracking attack on the pool state is less difficult than breaking the hash. In certain cases, this difficulty may be is reduced to 2^64 iterations. Instead, hash the entire pool in one go, then feedback the whole hash (160 bits) in one go. This will make backtracking at least as hard as inverting the hash. Signed-off-by: NMatt Mackall <mpm@selenic.com> Cc: Theodore Ts'o <tytso@mit.edu> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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