In (Nature) Science Report 5 (2015) 13653, Vadai, Mingesz and Gingl (VMG) introduce a new Kirchhoff-law-Johnson-noise (KLJN) secure key exchanger that operates with 4 arbitrary resistors (instead of 2 arbitrary resistance values forming 2 identical resistor pairs in the original system). They state that in this new, VMG-KLJN, non-equilibrium system with nonzero power flow, the security during the exchange of the two (HL and LH) bit values is as strong as in the original KLJN scheme. Moreover, they claim that, at practical conditions, their VMG-KLJN protocol “supports more robust protection against attacks”. First, we investigate the power flow and thermal equilibrium issues of the VMG-KLJN system with 4 arbitrary resistors. Then we introduce a new KLJN protocol that allows the arbitrary choice of 3 resistors from the 4, while it still operates with zero power flow during the exchange of single bits by utilizing a specific value of the 4th resistor and a binary temperature set for the exchanged (HL and LH) bit values. Then we show that, in general, the KLJN schemes with more than 2 arbitrary resistors (including our new protocol mentioned above) are prone to 4 new passive attacks utilizing the parasitic capacitance and inductance in the cable, while the original KLJN scheme is naturally immune against these new attacks. The core of the security vulnerability exploited by these attacks is the different line resistances in the HL and LH cases. Therefore, on the contrary of the statement and claim cited above, the practical VMG-KLJN system is less secure than the original KLJN scheme. We introduce another 2, modified, non-equilibrium KLJN systems to eliminate the vulnerability against some - but not all - of these attacks. However the price for that is the loss of arbitrariness of the selection of the 4th resistor and the information leak still remains greater than zero.

中文翻译：

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对带有任意电阻的“通用”KJLN 密钥交换器的评论：功率、阻抗、安全性

在 (Nature) Science Report 5 (2015) 13653 中，Vadai、Mingesz 和 Gingl (VMG) 介绍了一种新的 Kirchhoff-law-Johnson-noise (KLJN) 安全密钥交换器，它使用 4 个任意电阻器（而不是 2 个任意电阻值形成原始系统中有 2 个相同的电阻对）。他们指出，在这个具有非零功率流的新 VMG-KLJN 非平衡系统中，交换两个（HL 和 LH）位值期间的安全性与原始 KLJN 方案中的安全性一样强。此外，他们声称，在实际条件下，他们的 VMG-KLJN 协议“支持更强大的攻击防护”。首先，我们研究了具有 4 个任意电阻的 VMG-KLJN 系统的功率流和热平衡问题。然后我们引入了一个新的 KLJN 协议，它允许从 4 个电阻器中任意选择 3 个电阻器，而在单个位的交换期间，它仍然以零功率流运行，通过利用第四个电阻的特定值和为交换的（HL 和 LH）位值设置的二进制温度。然后我们证明，一般来说，具有超过 2 个任意电阻的 KLJN 方案（包括我们上面提到的新协议）容易利用电缆中的寄生电容和电感受到 4 种新的无源攻击，而原始的 KLJN 方案自然免疫对抗这些新的攻击。这些攻击利用的安全漏洞的核心是HL和LH情况下不同的线路电阻。因此，与上面引用的声明和权利要求相反，实际的 VMG-KLJN 系统不如原来的 KLJN 方案安全。我们介绍另外 2 个，修改后，KLJN 系统以消除针对某些（但不是全部）这些攻击的漏洞。然而，这样做的代价是失去了选择第 4 个电阻的任意性，并且信息泄漏仍然大于零。