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