Signed Hash Chain Sample Clauses

Signed Hash Chain. ‌ A web metering scheme can use digital signatures and hash chaining to construct non-repudiation evidences of visits as proposed by Xxxx and Xxx [62]. To exempt the user from producing a costly signature for each visit, a hash chain is pro- posed. The scheme is based on Lamport hash chaining technique for password authentication [83]. The scheme works as follows. Let H(x) be a one way function and Hm(x) is the successive application of H(x) m times. Initially, the visitor generates a random number s and computes Hm(s) where m is maximum number of visits and then registers the result at the webserver. Also, the visitor hashes the result with additional information like the webserver identifier and sends a signature of the hash to the webserver. For the next m visits, the visitor submits the previous corresponding hash input in the hash chain. That is, in the chain (V0 ... Vm), each value Vi of (V1 ... Vm), Vi = H (Vi−1). So in the first visit, the visitor submits to the webserver, Vm−1 which is Hm−1(s). The webserver checks that the one way function of received value Vm−1 is the previous received value (Hm(s)). If so, the webserver allows the visit and stores both values, and so on. If the webserver has V0 and Vm and the signature of Vm, it proves that the webserver has been visited m times. On the previous two schemes, the visitor used a private key to provide a signa- ture during the web interaction. The webserver checked and stored the received signature, and consequently allowed the visit. The received signature was used to constitute a web metering evidence as it is bound to the visitor identity. The audit agency was involved in the initialisation and verification of the scheme but not during the visitor-webserver interaction. Digital signature schemes and hash functions (and other compression functions like message authentication codes) can be grouped here together, as typically they take variable length input at the visitor side and produce a specified length output.