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From William A Rowe Jr <>
Subject Re: Good at assembler ? (Was:httpd - side channel attack - timing of digest comparisons)
Date Fri, 29 May 2015 16:38:54 GMT
> Secondly - when we get to the end of the shorter string; we can either
keep comparing to the last char or \0; or we go ‘modulo’ to the start of
the string. Now modulo is perhaps not ideal; and seems to affect the
pipeline on the XEON cpu (something I confess not to quite understand; and
I cannot see/replicate on ARM).

Comparing the same byte is easily optimized out.

What about looping over the same 16-byte micro-page we ended with, to avoid
fetching much earlier pages?  Truncate the address by nulling pointer bits
0x0f ?

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