AES is slow

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The CIFRA AES code you are using is quite slow. There may be better options out there...

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• ARM only, but pure ASM: https://github.com/Ko-/aes-armcortexm
• Bitcoin-core: https://github.com/bitcoin-core/ctaes ... but looks slow
• MbedTLS (already a submodule): libs/mpy/lib/mbedtls/library/aes.c
• C lib, smaller code (but meh otherwise): https://github.com/kokke/tiny-AES-c

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Challenges:

• aes-armcotexm doesn't have CBC mode, and incomplete CTR implementation (only whole blocks)

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https://github.com/BrianGladman/aes/blob/master/aes.h

• no ARM ASM, but still looks decent
• complete