  On today's Internet, combining the end-to-end security of TLS with Content
Delivery Networks (CDNs) while ensuring the authenticity of connections results
in a challenging delegation problem. When CDN servers provide content, they
have to authenticate themselves as the origin server to establish a valid
end-to-end TLS connection with the client. In standard TLS, the latter requires
access to the secret key of the server. To curb this problem, multiple
workarounds exist to realize a delegation of the authentication.
  In this paper, we present a solution that renders key sharing unnecessary and
reduces the need for workarounds. By adapting identity-based signatures to this
setting, our solution offers short-lived delegations. Additionally, by enabling
forward-security, existing delegations remain valid even if the server's secret
key leaks. We provide an implementation of the scheme and discuss integration
into a TLS stack. In our evaluation, we show that an efficient implementation
incurs less overhead than a typical network round trip. Thereby, we propose an
alternative approach to current delegation practices on the web.
