In this paper, an electronic signature algorithm, using a combined technology of digital signature, digital watermarking and time stamp, is presented. In this algorithm timestamp information is added to digital signature data, improving the signature safety and anti-offensive. A digital watermark embedding algorithm based on wavelets transform module maximum is designed. Using this algorithm the signature information can be embedded into the signature image as a watermark, enhancing the signature information hidden. The experiment shows that the algorithm can meet very well the requirements of contract signature in e-commerce transactions. This algorithm not only implements authentication, but also ensures the integrity and non-tampering of the contract.

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Combinatorial characterization of optimal authentication codes with arbitration was previously given by several groups of researchers in terms of affine a-resolvable $+$ BIBDs and $\alpha$ -resolvable designs with some special properties, respectively. In this paper, we revisit this known characterization and restate it using a new idea of GOB designs. This newly introduced combinatorial structure simplifies the characterization, and enables us to extend Johansson's well-known family of optimal authentication codes with arbitration to any finite projective spaces with dimension greater than or equal to 3.