Before:
- a separate Word element allocation of the underlying Vector<Word> was
necessary for every new word in a multi-word shift
- two additional temporary UnsignedBigInteger buffers were allocated
and passed through, including in downstream calls (e.g. Multiplication)
- an additional allocation and word shift for the carry
- FIXME note seems to point to some of these issues
After:
- main change is in LibCrypto/BigInt/Algorithms/BitwiseOperations.cpp
- one single allocation per call, using shift_left_by_n_words
- only the input "number" and "output" need to be allocated by the
caller
- downstream calls are adapted not to allocate or pass temporary
buffers
- noticeable performance improvement when running TestBigInteger:
0.41-0.42s (before) to 0.28-0.29s (after) Intel Core i9 laptop
Bonus: remove unused variables from UnsignedBigInteger::divided_by
- These were likely cut-and-paste artifacts from
UnsignedBigInteger::multiplied_by; not caught by "unused-varible".
NOTE: making this change in a separate commit than shift_right, even if
it touches the same file BitwiseOperations.cpp since:
- it is a "bonus" addition: not necessary for fixing the shift_right
bug, but logically unrelated to the shift_right code
- it brings a chain of downstream interface modifications (7 files),
unrelated to shift_right
This adds a thin wrapper to LibCrypto for generating cryptographically
secure random values and replaces current usages of PRNG within
LibCrypto as well.
The previous implementation of `ModularInverse` was flaky and did not
compute the correct value in many occasions, especially with big numbers
like in RSA.
Also added a bunch of tests with big numbers.
These changes are arbitrarily divided into multiple commits to make it
easier to find potentially introduced bugs with git bisect.Everything:
The modifications in this commit were automatically made using the
following command:
find . -name '*.cpp' -exec sed -i -E 's/dbg\(\) << ("[^"{]*");/dbgln\(\1\);/' {} \;
If they use up so much stack space, contain (sometimes several) loops, and take
a noticable amount of time anyway, then 'inline' is probably going to be ignored
by the compiler anyway.
ModularFunctions::random_number calls into AK::fill_with_random calls (on
Serenity) into arc4random_buf calls into Process::sys calls into
get_good_random_bytes, which is cryptographically secure.
This patchset adds a simple SignedBigInteger that is entirely defined in
terms of UnsignedBigInteger.
It also adds a NumberTheory::Power function, which is terribly
inefficient, but since the use of exponentiation is very much
discouraged for large inputs, no particular attempts were made
to make it more performant.
This change leads to between 10% and 35% performance improvement when executing
the RSA decryption method.
The main impact is to drastically reduce the number of allocations done in this
method from around 50% of the profile hits to less than 2%.
