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Based on the analysis of 6-digit one-time passwords (OTP) generated by DIGIPASS GO3 we were able to reconstruct the synchronization system of the token, the OTP generating algorithm and the verification protocol in details necessary for an attack. The OTPs are more predictable than expected. A forgery attack is described. We argue the attack success probability is much higher than it may be expected if all the digits are independently and uniformly distributed. The implications for the security of authentication are discussed and open questions are formulated.