Semiquantum key distribution (SQKD) allows two parties (Alice and Bob) to create a shared secret key, even if one of these parties (say, Alice) is classical. However, most SQKD protocols suffer from severe practical security problems when implemented using photons. The recently developed "Mirror protocol" [Boyer, Katz, Liss, and Mor, Phys. Rev. A 96, 062335 (2017)] is an experimentally feasible SQKD protocol overcoming those drawbacks. The Mirror protocol was proven robust (namely, it was proven secure against a limited class of attacks including all noiseless attacks), but its security in case some noise is allowed (natural or due to eavesdropping) has not been proved yet. Here we prove security of the Mirror protocol against a wide class of quantum attacks (the "collective attacks"), and we evaluate the allowed noise threshold and the resulting key rate.

翻译：半量子密钥分发（SQKD）允许两方（爱丽丝和鲍勃）建立共享的秘密密钥，即使其中一方（例如爱丽丝）是经典的。然而，大多数SQKD协议在使用光子实现时存在严重的实际安全性问题。最近开发的"镜像协议"[Boyer, Katz, Liss, and Mor, Phys. Rev. A 96, 062335 (2017)]是一种实验可行的SQKD协议，克服了这些缺点。镜像协议被证明是稳健的（即，被证明能抵抗包括所有无噪声攻击在内的有限类别攻击），但其在允许一定噪声（自然噪声或窃听所致噪声）情况下的安全性尚未得到证明。在此，我们证明了镜像协议对一大类量子攻击（"集体攻击"）的安全性，并评估了允许的噪声阈值及由此产生的密钥速率。