  A quantum string seal encodes the value of a (bit) string as a quantum state
in such a way that everyone can extract a non-negligible amount of available
information on the string by a suitable measurement. Moreover, such measurement
must disturb the quantum state and is likely to be detected by an authorized
verifier. In this way, the intactness of the encoded quantum state plays the
role of a wax seal in the digital world. Here I analyze the security of quantum
string seal by studying the information disturbance tradeoff of a measurement.
This information disturbance tradeoff analysis extends the earlier results of
Bechmann-Pasquinucci et al. and Chau by concluding that all quantum string
seals are insecure. Specifically, I find a way to obtain non-trivial available
information on the string that escapes the verifier's detection with at least
50% chance.
