What is the file "signature.asc" attached to email I receive from Kraken?

This is a PGP signature that can be used to verify the authenticity of automated emails sent from exchange@kraken.com. This helps prove that Kraken is the author of the email.

It's generated using both the content of the email and Kraken's PGP private key.

You can verify the signature of each email using PGP and the public Kraken PGP key.