Redactable Signature And Application In Transferable Offline Electronic Cash Design

In recent years,many governments,organizations and corresponding researchers have begun to explore the possibility of establishing a legal digital currency system.Existing electronic cash cannot be considered as legal digital currency because it cannot balance financial security(this is manifested in the fact that electronic cash is anonymous,easy to be used for illegal activities such as money laundering)and practicality(this is reflected in the fact that electronic cash does not have offline transferability).Therefore,this paper decided to build an electronic cash capable of acting as a legal digital currency(it uses redactable signature technology as a security tool and has offline transferability)and mainly does the following work:(1)By analyzing the shortcomings of Lamport digital signature scheme,this paper proposes a new digital signature scheme based on hash function,which is called Lamport Signature Scheme with Counter(LSC).By recording the number of 1-bits in the message to be signed,the LSC saves nearly 1/2 of the signature space,and the LSC retains the quantum resistance of the original scheme.Compared with other similar schemes,LSC has the highest security level and the highest utilization rate for the signature algorithm input space when the signature size is equivalent.The LSC occupies the smallest signature space for each bit of the useful message.Through the formal safety proof,this paper concludes that "as long as the hash function used by LSC is safe and effective,LSC is also safe".(2)This paper analyzes the existing problems of the existing redactable signature scheme and proposes the concept of fair redactable signature.Based on the concept of fair redactable signature,the definition and security model of the redactable signature are improved,and the application scenario of the redactable signature is extended.A fair redactable signature scheme based on LSC,named Redactable Lamport Signature Scheme with Counter,as RLSS,is proposed.The security of RLSS is also formalized in this paper.RLSS shows a particularly strong applicability where information is added after the document has been revised.(3)This paper uses RLSS to construct an electronic cash system,which includes five protocols:system initialization,account opening,withdrawal,payment and deposit.It is deduced from the security nature of RLSS and the various protocols of the system that this electronic cash is unforgeable,non-invasive,and cannot double use.More importantly,this electronic cash system achieves offline transfer characteristics,which makes this electronic cash have the potential to be equivalent to the physical currency.In addition,this electronic cash system is suitable for distribution by a powerful central organization and is practical.