OpenPGP

OpenPGP is a protocol that allows email users to sign and encrypt their emails. You may occasionally stumble upon an email including an attachment with a filename like signature.asc. This is usually a text file containing the digital signature of the email you are reading, including other attachments if present. There are applications available that can check the validity of the signature of the email. In order to do that for emails that I sent, you need my public key, which follows hereafter.

Wikipedia on OpenPGP