Abstract. This paper presents a robust software token that was developed to protect user’s digital identity by simple software-only techniques. This work is closely related to Hoover and Kausik’s software smart cards, and MacKenzie and Reiter’s networked cryptographic devices, in the fact that user’s private key is protected by postulating a remote server rather than tamper-resistance. The robust software token is aimed to be richer than the related schemes in terms of security, efficiency and flexibility. A two-party RSA scheme was carefully applied for the purpose, in a way of considering practical construction. This manuscript is an extended and revised version of the paper presented at ACISP 2003 conference.