On the Security of a Lattice-Based Multi-party Concurrent Signature Scheme

Fair exchange is essential in E-commerce, and concurrent signature realizes the fair exchange of digital signatures with removing the requirement of a trusted third party. Multi-party concurrent signature is an extension to the multi-user scenario. The security of existing multi-party concurrent signatures is mostly based on traditional hard problems that could be solved efficiently with quantum algorithms in a post-quantum world. Meanwhile, the lattice-based cryptography is considered to be resistant to quantum attack. Wang et al. proposed a lattice-based multi-party concurrent signature. We give the analysis of their proposed signature scheme and find that it is not secure since an inside adversary can forge the signature. Moreover, the initial signer can produce any signatures, instead of a signature on the original messages, if he is malicious.