[hybi] Performance of Vector XOR

["Bob Gezelter" <[e-mail]>]

Len, Tobias, Richard,

I would recommend extreme caution on using rough JavaScript or even
Python benchmarks as a test for the execution efficiency of the masking
operation (Note: I say this as one who is unconvinced of the benefits of
masking).

A well-written, straight vector XOR of a message should not be an
extremely expensive operation. I would be loath to believe that modern
processors cannot effectively perform this operation. With all due
respect to the implementers, it is far more likely that the JavaScript
(and quite possibly Python) use data structures and representations that
were not designed for this type of vector operation.

In a real situation, the XOR would be done in code that is likely
written in C/C++ or a similar language. If there is a real concern on
this issue, then the analysis should be done at the level of precisely
what machine instructions are actually being executed. As a former code
generator writer, I can attest that it is quite easy to gain or lose
efficiency at this level (for example, I would be unsurprised to
discover that JavaScript and Python are doing the XOR one byte at a
time, rather than in 64-bit chunks; that alone would account for nearly
an order of magnitude performance hit).

- Bob Gezelter, http://www.rlgsc.com