Voucher-based Schemes Sample Clauses

Voucher-based Schemes. ‌ Secret sharing schemes are classified under this category because the visitor re- ceives a secret from the audit agency which can be regarded as a voucher. The webserver here needs to receive a specific number of shares from visitors (thresh- old) upon their visits to be able to compute a required result. The result of the computation proves the webserver has indeed received the secrets (the visits). The majority of web metering schemes is based on secret sharing schemes. One of the early published web metering schemes in literature is by Xxxx and Xxxxxx [93] which was based on Xxxxxx Xxxxxxxxx secret sharing scheme [111]. In this scheme, the webserver needs to receive a specific number of shares from visitors to be able to compute a required result using Shamir scheme as evidence of the visits. To provide web metering evidence that a webserver has been visited a specific number of times, Secret sharing schemes can be used where its threshold denotes the specific number of visits. Further research continued on Naor and Pinkas work for example, Xxxxxxx work on web metering schemes [21, 18, 85, 16, 20, 17, 22]. More formally, Xxxxxx secret sharing works as follows. The secret is divided into n parts where the knowledge of k parts or more is adequate to compute the secret. Let randomly chosen k − 1 coefficients be a1, a2, ... ak−1 and a0=secret. Then, let the polynomial f(x) =a0+a1x+a2x2 ... ak−1xk−1(modp) where p is a large prime number. After that, n random inputs (r1...rn) are fed into the f (x) to give each visitor v a pair (rv, f (rv)). Once the webserver receives k pairs from visitors, the secret, a0, can be computed using Lagrange basis polynomials [14]. The required number of received pairs can be used to reconstruct the secret, by computing p(x), as follows. Qk−1(x − xj ) (x) = j=0 vi Qk−1(x − xj ) Σ k−1 p(x) = lvc(x)f (rvc) Also, Xxxxxx-Xxxxx threshold scheme [9] can be used as a web metering scheme as in the following two phases: the formation and secret recovery phases [82]. In the secret formation phase for the secret S, the audit agency chooses a prime p and numbers d1, d2..dn which satisfy the following five conditions. 1. For any chosen di, d1 < d2..< dn. 2. For any di and dj , where i does not equal j, the Greatest Common Divisor of di and dj is 1. 3. p must be a prime number i.e. the Greatest Common Divisor of di and p is 1 for all i.