Quantum cryptography: Security criteria reexamined
Dagomir Kaszlikowski, Ajay Gopinathan, Yeong-Cherng Liang, L. C. Kwek, Berthold‐Georg Englert · Physical Review A · 2004
We find that the generally accepted security criteria are flawed for a whole class of protocols for quantum cryptography. This is so because a standard assumption of the security analysis, namely that the so-called square-root measurement is optimal for eavesdropping purposes, is not true in general. There are rather large parameter regimes in which the optimal measurement extracts substantially more information than the square-root measurement.