The past history of Digital Signature

An original signer allows a designated person, called a proxy signer,

to sign a message on behalf of original signer. Proxy signatures have two properties, one is unforceability, and another is verifiability.

Proxy signature is original singer can not sign the document cause by some reason. And then the sign authority transferred to another proxy signer. Proxy singer sign the document efficiency same as original signer sign the document. These signatures have a problem what if original signer purposely falsely incriminate proxy signer. The proxy signature is non-repudiation. So the Mambo et al [10] proposed a method, call a Proxy-protected Proxy signature. This kind of stamped signature is mainly, the agent joins him self’s own gold key of secret (Secret key) at the time of stamped signature, when act for stamped signature in verification except that the persons who can verify primitive stamped signature agree to this stamped signature, because sign to join the agent's gold key of secret in the course, so can verify the agent at the same time, frame the agent on purpose for the person who prevents primitive stamped signature from.

In the society now, an official document often needs through many people's signature just validity and responsible for together, so, a lot of are proposed the colony and several signature technology that many people lead. In 1991, Chaum and Heyst [22] propose the signature of a kind of new-type attitude, is called colony's signature. The so-called colony's signature is the mechanisms of a kind of combination evidence (Credential) and member's identity authentication (Authentication).

Utilize this mechanism, can prove to the person who prove that he belongs to this colony while belonging to a certain member of this colony and don't will expose its identity. When there are disputes to take place,

the identity of signature of this colony signature person can just be by its identity that colony's administrator (Group authority) or but all member's cooperation are open. We can sum up the characteristic with the following of colony's signature:

(1) Only by belonging to the members of this colony can it sign.

(2) The recipient of signature can verify the exactness of this colony signature, the identity of the person who calculates signature in but unable to be signed by this colony.

(3) Have dispute emerge, is it can calculate by colony this who sign to sign. However, only colony's administrator or the members of colonies work in concert and can calculate.

But, if colony members change in their system, every member must alter its gold key. In addition, colony of them stamped signature system unable to let colony administrator prove colony stamped signature the lucky number identity of chapter person. Colony stamped signature system proposed the above belong to getting interactive system all, so efficiency it’s good. Several is improved the mechanism to also propose, but mostly unable to meet all characteristics afterwards. In 1999, Camenisch and Michels [23] proposed a method of improving. But, in their system, have the following disappearances: Its calculation amount and information are also too large in length.

In 1997, the people, such as Park [24], etc. proposed that one regards identity as the colony stamped signature system of the base. The major advantage of this system is the open gold key of the person who is signed is but information need not be verified in its identity (ID), so not need to set up one by common authentication and disclosing the gold key

file enormously publicly of letter unit. But there is a serious problem in this colony stamped signature system which regards identity as the base; Namely the persons who sign must use the identity gold key of the members of colonies while signing, cause colony members to lose efficiency like changing colony's stamped signature. In addition, this length of stamped signature produced of colony stamped signature system will increase with member's figure.

Threshold signature call colony lead stamped signature

(Group-oriented signature) [25, 26, 27]. And it is that members in the colony signed the same file that the threshold is worth several stamped signature ways, but the threshold is worth not needing all members in the colony to all participate in several stamped signature, only have to exceed threshold value in number of members. It is that the person who proves does not know that there are those members that participate in signing that it has a characteristic in addition. Because the threshold is worth not needing all members in the colony to all participate in several-stamped signature, and the persons who prove do not know that those members participate in signing, so cause it while disputing, it is unable to learn that those members participate in signing the file actually in a colony. For offer different application, have so-called traceable threshold of person who sign (Traceable signer) worth several proposition to sign art of composition [28, 29]. That is to say, the persons who prove can also know that those members participate in signing the file actually at the same time while verifying colony's stamped signature of threshold value.

Threshold proxy signature [16, 30] as its name is combining the

Group-oriented signature and designs the idea with proxy signature. So the signature method of threshold proxy signature that is a proxy signer who appoints a colony with many people of persons is signed by original signer. The number of members in this colony can produce legal proxy signature while exceeding threshold value. The verifier is unable to know that those members participate in signing.