Key verification in AES

Question

If the user enters a wrong key for AES decryption, some garbage data is generated. I want to verify the given decryption key and throw an error if the key is incorrect. How

Answer 1

One common way used to verify if a key is correctly entered, without revealing the actual key, is by use of a KCV (Key Check Value). When you create the key you would at the same time calculate the KCV, when the key is then entered manually, you can verify the entry by re-calcuylating the KCV. This is eg. used when entering keys manually into HSM's from physical key letters.

To calculate a KCV for an AES key you encrypt an empty (0x00) block with the key and the first 3 bytes of the resulting encrypted block is then the KCV.

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