New linking schemes for digital time -

Binary Linking Schemes (BLS) for digital time-stamping 3] provide (1) relative temporal authentication to be performed in logarithmic time, and (2) time-certiicates of reasonable size, which together with the data published in a widely available medium enable the veriier to establish their relative temporal positions, even if the database held by the Time-Stamping Service (TSS) ceases to exist. We show that the size of a time-certiicate (X) of a document X in the scheme presented in 3] is bounded by 4 log 2 N where k is the output size of the hash function and N is the number of time-stamps issued. We then present a new BLS with (X) 6 log 2 3 k log 2 N and prove that the presented scheme is optimal in that sense.