Development of Time-Stamped Signcryption Scheme and its Application in E-Cash System

A signcryption scheme combining public key encryptions and digital signatures in one logical step can simultaneously satisfy the security requirements of confidentiality, integrity, authenticity and non-repudiation and with a cost significantly lower than that required by the traditional "signature followed by encryption" approach. This thesis presents a new generic concept of time-stamped signcryption scheme with designated verifiability. Here an authenticated time-stamp is associated with the signcrypted text which can only be verifiable by a specific person, known as the designated verifier. The time-stamp is provided by a trusted third party, namely, Time Stamping System (TSS). The scheme is proved to be secure, as, no one, not even the signcrypter or TSS can produce a valid signcrypted text on behalf of them. We analyzed the security of the proposed scheme and found that it can withstand some active attacks. This scheme is resistant against both inside and outside attacks. The security of our scheme is based upon the hardness of solving Computational Diffie Hellman Problem (CDH), Discrete Logarithm Problem (DLP) and Integer Factorization Problem (IFP). The proposed scheme is suitable in scenarios such as, on-line patent submission, on-line lottery, e-cash, e-bidding and other e-commerce applications. Also we propose an e-cash system based on our proposed time-stamped signcryption scheme which confirms the notion of e-cash securities like anonymity of the spender, unforgeablity of the digital coin, prevention of double spending

On the design of time-stamped signatures

[[abstract]]To ensure integrity and originality of digital information, digital signatures were proposed to provide both authority and non-repudiation. However, without an authenticated time-stamp we can neither trust signed documents when the signer's signature key was lost, stolen, or accidentally compromised, nor solve the cases when the signer himself repudiates the signing, claiming that he has accidentally lost his signature key. Based on relative temporal authentication, several linking schemes for digital time-stamping have been proposed to solve this problem. However, these schemes suffer from the forward forgery which is an attempt to stamp a present time-stamp on a past document by an unauthorized one. In addition, the verification cost in these schemes is too high because it is dependent upon the number of the issued time-stamps. In this paper, we propose four time-stamped signature schemes that are based on absolute temporal authentication. These proposed schemes are very efficient in verifying the' validity of time-stamped signatures and are quite secure against the forward forgery. It is natural that the time-stamped signature schemes based on absolute temporal authentication suffer from the weakness when the signer colludes with the Time-Stamping Service. To combat the collusion problem, time-stamped signature schemes with hybrid temporal authentication are therefore proposed.[[fileno]]2030230010022[[department]]資訊工程學

On the Design of Time-Stamped Signatures

[[abstract]]To ensure integrity and originality of digital information, digital signatures were proposed to provide both authority and undeniability. However, without an authenticated time-stamp we neithe rcan trust signed documents when the signer’s signature key was lost, stolen, or accidentally compromised, nor solve the cases when the signer himself repudiates the signing, claiming that he has accidentally lost his signature key. Based on relative temporal authentication, several linking schemes for digital time-stamping have been proposed to solve this problem. However, these schemes suffer from the forward forgery which is an attempt to stamp a present time-stamp on a past document by an unauthorized one. In addition, the rification cost in these schemes is too high because it is dependent upon the number of the issued time-stamps. In this paper, we propose four time-stamped signature schemes that are based on absolute temporal uthentication. These proposed schemes are very efficient in verifying the validity of time-stamped signatures and are quite secure against the forward forgery. It is natural that the time-stamped signature schemes based on absolute temporal authentication suffer from the weakness when the signer colludes with the Time-Stamping Service. To combat the collusion problem, time-stamped signature schemes with hybrid temporal authentication are therefore proposed