Security Analysis of an Arbitrated Quantum Signature Scheme with Bell States

Recently, to resist attacks using the anticommutativity of nontrivial Pauli operators, an arbitrated quantum signature scheme with Bell states (Int. J. Theor. Phys. 53(5), 1569-1579 2014) was proposed. The scheme randomly adds Hadamard operations to strengthen the quantum one-time pad encryption. Based on this, it claimed that the scheme could resist the receiver's existential forgery and no party had chances to change the message without being discovered. This paper introduces two security issues of the scheme: It can't resist the signer's disavowal and the receiver's existential forgery. Furthermore, we show that the scheme is still vulnerable to the receiver's existential forgery even if the Hadamard operation in the encryption algorithm is replaced with any 2nd-order unitary operation.