| dc.description.abstract | The design of proxy signature was first considered in 1996
by Mambo, Usuda, and Okamoto. In a proxy signature scheme, an
original signer can delegate one or more proxy signers to sign on behalf of the original signer. The concept of proxy signature was been independently posed out by Yen in 1994 in his Ph.D. thesis.
Up to now, there are five categories of proxy delegation have
been proposed, named as fully delegation, partial delegation, delegation by warrant, partial delegation with warrant, and threshold delegation. Each type of proxy delegation has its security assumption and properties.
Generally speaking, the partial delegation with warrant is
the most efficient scheme, and provides a reasonable way to
regulate the delegation. The advantage of delegation by
warrant is that it can be implemented by an ordinary signature
scheme without any modification. Each kind of proxy signature
scheme has its merit and limitation.
Till now, a lot of related works can be found in the literature. In Chapter 3, a survey on those schemes is done in this thesis and we try to formalize the generation
function of proxy signing key for both partial delegation and partial delegation with warrant. Then, a Meta-proxy signature scheme is obtained.
In Chapter 4, an efficient proxy signature scheme in the form of delegation by warrant is proposed. It is shown that the scheme is more efficient for some variations with a special feature of it combined verification.
In most conventional situations, it can restrict the proxy
delegate within a permitted period by using a delegation warrant. In the warrant, the proxy signer's ID, original signer's ID, and delegation period are included. However, a proxy signer can sign on any number of messages at any time. It is an important issue on how to develop a proxy signature scheme that can restrict the proxy signer's behavior, for example to sign for a number of times. In Chapter 5, a proxy signature scheme with time limitation will be suggested. It enables an original signer to delegate a proxy signer to sign for a predetermined number of times.
In the scenario, there should be some penalty for the proxy
signer when she/he breaks the rule of the delegation. For
example, the original signer (or even anyone) can derive the
secret key of the dishonest proxy signer as suggested by Yen in
1994. However, the proposed scheme in this thesis cannot reach the above requirement. Thus, even if the proxy signer had broken the rule of delegation, no one can derive the secret key of proxy signer. However, the number of proxy signatures signed can be countable and traceable. | en_US |