Self-Delegation with Controlled Propagation - or - What If You Lose Your Laptop

We introduce delegation schemes wherein a user may delegate certain rights to himself, but may not safely delegate these rights to others. In our motivating application, a user has a primary (long-term) key that receives some personalized access rights, yet the user may reasonably wish to delegate these rights to new secondary (short-term) keys he creates to use on his laptop when traveling, to avoid having to store his primary secret key on the vulnerable laptop. We propose several cryptographic schemes, both generic ones under general assumptions and more specific practical ones, that fulfill these somewhat conflicting requirements, without relying on special-purpose (e.g., tamper-proof) hardware.