Make bin2hex() and hex2bin() timing safe #1453
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See also: http://markmail.org/message/4wwjnqr3sz6cqaxh
bin2hex()is using a lookup table; there is potential for a cache timing attack if not aligned on 16 byte boundary.Solved via explicit alignment. (No perf change)
hex2bin()is using branches to differ between 0-9 and a-f/A-F. Simple timing attack potential.Using a branchless construct solves this [The only branch is early abort on malformed hex, which is not an issue]. (Performance in best-case is worse, but better than average-case [at least locally]. Currently average case has about 20% mispredictions (tested on just normal text), which makes it slower than the branchless code.)
That way
hex2bin()even has a slight performance benefit in addition to time safety.