[Cryptography] Bent, crooked, and twisted functions

[Ferecides de Siros]

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Pierre,

Great to hear you're using the tool!

I use the same simple approach for all my code:
**License:** This is free and unencumbered software released into the public 
domain. Anyone is free to copy, modify, publish, use, compile, sell, or 
distribute this software, either in source code form or as a compiled binary, 
for any purpose, commercial or non-commercial, and by any means.

**Julia translation:** Absolutely! The core analysis is straightforward:
- - For each input difference a ≠ 0, compute derivatives D_aF(x) = F(x⊕a)⊕F(x)
- - Count distinct derivatives (should be 2^(n-1) for APN)
- - The Rust implementation mirrors this directly.

**Function duplication:** Thanks for catching that - the Gold and quadratic 
functions were indeed just placeholders.

**Your 4-bit results:** Interesting that the canonical twisted function shows 
different patterns than the 3-bit version. The [3,3,3,3,3,2,3] pattern 
suggests consistent but imperfect nonlinearity.

The tool seems to be working well for your research. I'm just happy to 
contribute to something I find mathematically beautiful.

Best,
Hitokiri
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