Upper bounds of a class of imperfect quantum sealing protocols

The model of the quantum protocols sealing a classical bit is studied. It is shown that there exist upper bounds on its security. For any protocol where the bit can be read correctly with the probability $\alpha$, and reading the bit can be detected with the probability $\beta$, the upper bounds are $\leqslant 1/2$ and $\alpha +\beta \leqslant 9/8$.Comment: 5 pages, 1 figure. Add an example on how to break the majority voting schem

Comment on "Unconditionally secure commitment in position-based quantum cryptography"

We show that a recently proposed relativistic commitment scheme [Sci. Rep. 4, 6774 (2014). arXiv:1406.6679] is insecure against the cheating of the committer.Comment: 1 pag