Possible Vulnerabilities

[NotAFile]

I saw this in f-droid and felt like checking your crypto code.

I'm not familiar with the Java crypto libraries, but from what I can tell, it has a number of crypto issues:

• it appears you are using SHA256 for key derivation. This is very fast to compute (and brute force) and unsuitable for deriving an AES key from. Consider using, say, PBKDF2 instead.
• You are using CBC, however it appears you are not using a Message Authentication Code to verify the integrity of the message. This means your code is, at least theoretically, vulnerable to a padding oracle, and message modification. You can verify the integrity of the ciphertext with e.g. a sha256 HMAC to prevent this.
• it appears you are using a hardcoded IV. This is un-ideal in general, but with some modes, like CBC, it is potentially catastrophical, in this case if the same message is encrypted with multiple keys.