中文摘要：

iJam是一种与信道变化快慢无关、且能够快速生成物理层密钥的新技术。在iJam方案中，发送者连续发送两份相同的OFDM符号，接收者随机干扰每对采样点中的一个。合法接收者可以利用干扰信息重构密钥信息，而窃听者因不知干扰符号的位置而无法进行有效重构。然而，iJam方案的安全性与窃听者的位置紧密相关。尽管iJam采取双向交换密钥等机制克服了单窃听者的位置敏感问题，但是iJam方案的安全问题仍然存在。为攻击iJam，本文提出了一种双窃听者合作攻击方法，两个分别位于Alice、Bob端的窃听者合作对iJam进行攻击。仿真结果表明：双窃听者合作攻击方法可有效破解合法用户协商的密钥。

英文摘要：

The iJam scheme is a novel physical-layer approach for secret key generation, where the generation of secret bits can be very fast and essentially independent of channel variations. The basic idea is that Alice, as the legitimate user, sends an 0FDM symbol twice and Bob, as the legitimate receiver, randomly jams either the original transmission sample, or the corresponding sample in the repetition. Since Bob knows the locations of jamming, it can pick the correct samples from the received signal, and restructure them to obtain a clean signal. But the eavesdropper does not know which received signal is jammed and which one is clean, so it cannot correctly decode the data. However, the robustness of jamming de- pends on the eavesdropper＇s location with respect to the sender and jammer. Although i Jam takes two-way exchange to overcome the eavesdropper position sensitive issues, the security of iJam has not been resolved fully. In order to crack iJam scheme completely, we propose a double-eavesdroppers cooperative attack, which can be well employed to crack the i Jam scheme. Extensive simulation results validate our claim.