Quantum Inf Process (2017) 16:96
Comment on “quantum oblivious transfer: a secure
Guang Ping He
Received: 16 December 2016 / Accepted: 16 February 2017 / Published online: 24 February 2017
© Springer Science+Business Media New York 2017
Abstract We study the entanglement-based attack on a recently proposed quantum
oblivious transfer (OT) protocol (Nagy and Nagy in Quantum Inf Process 15:5037,
2016). While in secure OT, Bob’s probability of obtaining Alice’s secret bit unam-
biguously should be limited to 50%, we show that if Bob has the technology to handle
5-body entangled states in the current protocol, then he can increase this probability
to 64.6%. More importantly, in contrast to what the authors claimed, increasing the
number of qubits used in the protocol cannot increase the hardness of Bob’s attack.
Keywords Oblivious transfer · Bit commitment · Entanglement
Oblivious transfer (OT) is a cryptographic task with the following goal: Alice sends
Bob a secret bit b, in such a way that at the end of the protocol, Bob obtains b
unambiguously with probability 1/2, while Alice remains oblivious as to whether
Bob has learned b or not.
It was well known that OT protocols built upon bit commitment (BC) cannot be
unconditionally secure. Recently, Nagy et al.  proposed a quantum OT protocol
which does not rely on BC and proved that it is secure against individual measurements,
as well as 2-qubit entanglement-based attacks. There is no doubt that the proposal is
This work was supported in part by the NSF of Guangdong Province of China under Grant No.
Guang Ping He
School of Physics, Sun Yat-sen University, Guangzhou 510275, China