Authentication of LZ-77 compressed data

The formidable dissemination capability allowed by the current network technology makes it increasingly important to devise new methods to ensure authenticity. Nowadays it is common practice to distribute documents in compressed form. In this paper, we propose a simple variation on the classic LZ-77 algorithm that allows one to hide, within the compressed document, enough information to warrant its authenticity. The design is based on the unpredictability of a certain class of pseudo-random generators, in such a way that the hidden data cannot be retrieved in a reasonable amount of time by an attacker (unless the secret bit-string key is known). Since it can still be decompressed by the original LZ-77 algorithm, the embedding is completely "transparent". Preliminary experiments show also the degradation in compression due to the embedding is almost negligible