A method and system for authenticating a message is described, in which the message contains a network address, at least a portion of which is a digital fingerprint. Embedded in the message is data, such as a code, that indicates the size of the digital fingerprint. A device receiving the message uses the size data and, for example, the public key of the sender to attempt to reproduce the digital fingerprint. If successful, the device receiving the message verifies the identity of the sender.