Graz University of Technology
Proxy signatures allow an entity (the delegator) to delegate the user signing capabilities to other entities (called proxies), who can then produce signatures on behalf of the delegator. Typically, a delegator may not want to give a proxy the power to sign any message on their behalf, but only messages from a well defined message space. Therefore, the so called delegation by warrant approach has been introduced. Here, a warrant is included into the delegator's signature (the so called certificate) to describe the message space from which a proxy is allowed to choose messages to produce valid signatures for.