Should we use a different key to encrypt images or the same key for signing?

[zhiyong-ft]

Hi,

I have tried using either a separate key or the same key for signing images, both approaches work just fine. My question is, from security's perspective, which is better practice?

My concern about using the same key for both signing and encryption is that both private and public key will co-exist in bootloader. On the other hand, if someone already acquired a copy of the bootloader, then it doesn't matter whether the public and private key are actually a pair.

So please advise.

Thanks.

[naNEQ]

In general, I think the best security practices say to use a key pair for a single purpose only. Thus, from that perspective, it would be better to use different keys.

In our case, I'm thinking to have each device has its own key for encryption (not provided by me from the outside), so inherently, I will have different keys for signing and encryption.