For the purpose of deterring unauthorized duplication and distribution of multimedia contents in e-commerce, some Buyer-seller watermarking protocols which combine of traditional watermarking and fingerprinting techniques have been proposed, However, previous protocols have potential risk from trust third party (TTP) because all entities (including multi-buyers and multi-sellers) mentioned in protocol construct a star topology like connection, in which the watermark certification authority (WCA) serves as the central point in the interaction and therefore its availability probably turns out to be the vital bottleneck of reliability and efficiency to the whole system. Secondly, WCA holds entire information about watermark used by Buyers so that an innocent Buyer can be found as guilty if WCA collude with the Seller. In this paper, we propose a watermarking protocol to address the problems using cryptographic technologies in phase of watermark generation. The result is a TTP-independent and collusion-secure buyer-seller watermarking protocol.