Document Authentication Scheme Using Characters Metrics

In this paper, we propose a document authentication scheme, in which the document data has PDF format. The proposed scheme is an improved version of Zhupsilas document protection scheme. In Zhupsilas scheme, the render sequence is encoded, such that a predefined character of the render sequence is permuted by secret key. This permutation is then used as authentication code. Their scheme has two inconveniences for practical applications: The first one is that the file size of encoded document is considerably increased compared with the original one, the second one is that the structure of encoded render sequence is unnatural, and as consequence, it can be detected easily by third party and reverse engineering can be applied to tamper the document. To solve these problems, this paper propose a document authentication scheme, in which the encoded sequence is kept in its natural structure and the file size of the encoded document is not increased.