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First, the obvious advice is not to use this in practice. Rolling your own is fine for learning, but you should use standard primitives when you need actual security. E.g. one from SP 800-90A which poncho linked in comments. Now, some observations. I haven't read all your code, so I may misunderstand things. Is this a good way to whiten the data? Is ...


2

Like said in the comments, a 256-bit message is two blocks of AES, no matter the keysize. The main issue with ECB mode (i.e. using AES directly on 128-bit blocks) is that you leak whether two blocks are equal. When encrypting perfectly random data, that means there's a $2^{-128}$ chance the two parts of the key are equal, and the attacker knows that. The ...


2

I would advise a different solution. You either generate a master-key (or key set) or derive one from a user password (e.g. via PBKDF2 or SCrypt). For each file to encrypt you generate a random key (file key) and nonce ad-hoc, and encrypt the file with that key, using an AEAD scheme. The random file key is encrypted with you master key and put at the ...



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