Aspects of the disclosure are related to a method for verifying whether a message was digitally signed by a user. The example method comprises: receiving a public key of a public-key signature scheme and one or more pieces of plaintext identification information associated with the user; applying a hash scheme to a combination of the public key and the one or more pieces of plaintext identification information, the hash scheme yielding a hash result; determining whether the hash result satisfies one or more criteria; determining whether the public key is associated with the user based on the determination of whether the hash result satisfies the one or more criteria; and verifying a digital signature of the message with the public key.