2123: Improve the speed of bit flipping code

[cakekoa]

What does this PR do?

Fixes #2123.

Improves the ransomware encryption performance by about 2-3x via the following improvements (in order of effectiveness):

• Remove a function call
• Use a generator
• Use a more efficient flip calculation (subtraction instead of xor)

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the CHANGELOG.md updated to reflect the changes?
• Was the documentation framework updated to reflect the changes?
• Have you checked that you haven't introduced any duplicate code?

Testing Checklist

• Added relevant unit tests?
• Have you successfully tested your changes locally? Elaborate:

  Tested by running the unit tests, running a script to benchmark the performance improvement, and testing the encryption of a file.

• If applicable, add screenshots or log transcripts of the feature working

  $ python3.7 ./test_bit_flip.py
  New method: 1.1626720659987768
  Old method: 2.61535847299092
  speedup: 2.2494377817052253
  $ python3.7 ./test_bit_flip.py
  New method: 0.9523072919982951
  Old method: 2.428888782989816
  speedup: 2.550530488843683
  $ python3.7 ./test_bit_flip.py
  New method: 0.9450294990092516
  Old method: 3.04705688499962
  speedup: 3.224298170791587
  $ python3.7 ./test_bit_flip.py
  New method: 1.3276102009986062
  Old method: 2.5821857940027257
  speedup: 1.94498791291333
  $ python3.7 ./test_bit_flip.py
  New method: 1.3388573650008766
  Old method: 2.565408591006417
  speedup: 1.916117921198228
  

[codecov]

Codecov Report

Merging #2204 (2b5718f) into develop (2edaf52) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #2204      +/-   ##
===========================================
- Coverage    57.17%   57.16%   -0.01%     
===========================================
  Files          501      501              
  Lines        13440    13439       -1     
===========================================
- Hits          7684     7683       -1     
  Misses        5756     5756              

Impacted Files	Coverage Δ
monkey/infection_monkey/utils/bit_manipulators.py	100.00% <100.00%> (ø)

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[mssalvatore]

Maybe try this and see if performance changes:

Suggested change

	return bytes(generate_flipped_bits(data))
	return bytes(map(lambda byte: 255 - byte, data))

We could also try:

Suggested change

	return bytes(generate_flipped_bits(data))
	from functools import partial
	from operator import sub
	flip_bits = partial(sub, 255)
	return bytes(map(flip_bits, data))

[cakekoa]

The map call is actually about 25% slower than the generator:

$ python3.7 ./test_bit_flip_new.py 
Generating random data...
Testing encryption methods...
New method: 21.68712888698792
Old method: 16.69294242199976
speedup: 0.7697165682459411
$ python3.7 ./test_bit_flip_new.py 
Generating random data...
Testing encryption methods...
New method: 21.919233062013518
Old method: 16.677228108019335
speedup: 0.7608490708062826

The use of the partial function improves the map call slightly, but it's still 20% slower than the generator:

$ python3.7 ./test_bit_flip_new.py 
Generating random data...
Testing encryption methods...
New method: 21.326405769999838
Old method: 17.232965190021787
speedup: 0.8080576434620619
$ python3.7 ./test_bit_flip_new.py 
Generating random data...
Testing encryption methods...
New method: 21.268566457991255
Old method: 16.70874281899887
speedup: 0.7856073822371269