Messages in this thread | | | Date | Tue, 31 Mar 2020 00:27:38 +0000 | From | George Spelvin <> | Subject | Re: [RFC PATCH v1 44/50] arm64: ptr auth: Use get_random_u64 instead of _bytes |
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On Mon, Mar 30, 2020 at 07:32:37PM +0000, George Spelvin wrote: > On Mon, Mar 30, 2020 at 11:57:45AM +0100, Mark Rutland wrote: >> As I am unaware, how does the cost of get_random_bytes() compare to the >> cost of get_random_u64()? > > It's approximately 8 times the cost.
Just a expand on on a point I may have left unclear: One get_random_bytes(), for a length up to 32 bytes, is approximately 8x the one get_random_u64(). (Then it jumps to 16x for up to 96 bytes.)
Since were're using *two* get_random_u64() calls to replace one get_random_bytes(), it's a 4x cost difference between the two alternative ways of generating a 128-bit key.
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