In this paper, we propose an implementation of secure watermarking protocol using cryptographic technologies for use in real-life Internet retails market of digital contents, in which there is no trust assumption between a customer and a digital contents provider. The blind RSA decryption algorithm is used in our scheme to doubly lock the information by the public key of the content provider and the secret numbers of the customer separately. The privacy of watermark pattern is maintained, while the digital rights of the contents provider are protected. This is achieved by allowing the customer to choose a secret pattern of watermark combination unknown to the content provider. Consequently, the quality of the watermarked digital contents can be guaranteed. We show that the protocol is secure against any possible attacks from the customer and the content provider. Moreover, the dispute resolution process becomes mechanical.