Security Analysis on Secure Untraceable Off-line Electronic Cash System

In 2013, Baseri et al. proposed an untraceable off-line electronic cash scheme from the RSA cryptosystem. They used a method that injects the expiration date and the spenders identity onto the coin to prevent double spending. The authors claimed that the scheme provides the properties of anonymity, unforgeability, double spending detection, and date attachability. Unfortunately, we find that there are security flaws in terms of verifiability, unreuseablity, and unforgeability. First, the verifiable method of e-cash in their scheme is not correct according to Euler’s Theorem. Second, malicious spenders can inject a false identity in the withdrawal phase due to the homomorphic property of modular operation. Therefore, coins can be doubly spent without being detected. Finally, a malicious spender or merchant can forge valid coins using existing coins.