在AES 256 BIT中使用IV和密钥派生

Question

I'm developing a php system where all data is encrypted by a key derived from the user's password. I've already been able to derive the key, but to encrypting data with AES requires the key and IV. That is where my doubt was born: In this case, I suppose I should store IV to decrypt the data later. Where do I store? In the database or in a file on the server? Or is it not correct to store the IV and is there another way to get the same IV for the same key?

Answer 1

Don't derive an IV from the same source that you derive the key from. You should use a randomly generated IV for each encryption operation and simply store the IV with the ciphertext.

It is common to simply prepend the IV to the ciphertext so that it can be retrieved easily when the data needs to be decrypted. The IV does not need to be secret, so the above method is completely secure.

To reiterate, because it is important, do not derive the IV from a KDF or similar, always randomly generate a new IV for each encryption operation.