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Instead of the basic square-and-multiply strategy which requires a square and a multiply per exponent bit (i.e. two modular multiplications per bit in total), we instead reduce to a square per exponent bit and an extra multiply only every 5 bits, because the value we're multiplying in is derived from 5 of the exponent bits at once via a table lookup. To avoid the obvious side-channel leakage of a literal table lookup, we read the whole table every time, mp_selecting the right value into the multiplication input. This isn't as slow as it sounds when the alternative is four entire modular multiplications! In my testing, this commit speeds up large modpows by a factor of just over 1.5, and it still gets a clean pass from 'testsc'.
This is the README for PuTTY, a free Windows and Unix Telnet and SSH
client.
PuTTY is built using CMake <https://cmake.org/>. To compile in the
simplest way (on any of Linux, Windows or Mac), run these commands in
the source directory:
cmake .
cmake --build .
Documentation (in various formats including Windows Help and Unix
`man' pages) is built from the Halibut (`.but') files in the `doc'
subdirectory using `doc/Makefile'. If you aren't using one of our
source snapshots, you'll need to do this yourself. Halibut can be
found at <https://www.chiark.greenend.org.uk/~sgtatham/halibut/>.
The PuTTY home web site is
https://www.chiark.greenend.org.uk/~sgtatham/putty/
If you want to send bug reports or feature requests, please read the
Feedback section of the web site before doing so. Sending one-line
reports saying `it doesn't work' will waste your time as much as
ours.
See the file LICENCE for the licence conditions.