Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | [PATCH v3 0/3] random: Account for entropy loss due to overwrites | Date | Sat, 27 Apr 2013 15:44:36 -0700 |
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From: "H. Peter Anvin" <hpa@linux.intel.com>
When we write entropy into a non-empty pool, we currently don't account at all for the fact that we will probabilistically overwrite some of the entropy in that pool. This means that unless the pool is fully empty, we are currently *guaranteed* to overestimate the amount of entropy in the pool!
This version of the patchset avoids manually duplicating information by using a macro. This removes *all* dynamic computation of derived pool information and replaces them with static information: on just about every architecture accessing pointer+offset is no more expensive than just plain pointer, and this lets us get the information we actually need from the start.
This version of the patchset adds handling of fractional bits, so that we can continue to add a single bit of entropy without it being rounded down to zero. This version has 3 bits of fraction, which means that with a 4096-bit input pool the multiply still cannot overflow 32 bits; if we want to add the capability of crediting fractional bits of entropy, which may be useful in itself, then we probably need more bits of fraction and would have to use a 64-bit multiply and shift.
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