https://github.com/jesseemond/break-substitution-cipher

Break substitution cipher using stochastic optimization
https://github.com/jesseemond/break-substitution-cipher

Last synced: about 17 hours ago
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Break substitution cipher using stochastic optimization

• Host: GitHub
• URL: https://github.com/jesseemond/break-substitution-cipher
• Owner: JesseEmond
• Created: 2021-03-07T19:03:02.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2021-03-07T19:03:19.000Z (over 3 years ago)
• Last Synced: 2024-10-11T20:36:33.364Z (about 1 month ago)
• Language: C++
• Size: 1.24 MB
• Stars: 0
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
Implementation based on

http://practicalcryptography.com/cryptanalysis/text-characterisation/quadgrams/#a-python-implementation

https://planetcalc.com/8045/

English quadgram frequencies from:

http://practicalcryptography.com/cryptanalysis/letter-frequencies-various-languages/english-letter-frequencies/

- First implemented in Python (`solve.py`), got ~6,350 attempts/s

- Re-implemented in C++ (`main.cpp`) (representing ngram log-probs as `unordered_map`), got ~39,700 attempts/s

- Represented n-grams as ints (`WXYZ -> W*26^3 + X*26^2 + Y*26 + Z`), got ~69,000 attempts/s

- Represented n-gram log-probs in a fixed array (of size `26^4`) got **~735,000** attempts/s

- Re-used plaintext string when decrypting, got **~950,000** attempts/s.