A2：模拟恶意硬件

导读

论文研究如何在芯片设计阶段植入模拟电路形式的恶意硬件后门，使其难以被常规检测发现。核心做法是用简单电容充当计数器：多次特定条件后累积电荷，最终放电并改变芯片状态，从而触发恶意行为。评论认为这类故意植入的后门比 rowhammer 等意外故障更隐蔽，并可启发电源管理等更微妙的攻击。

HN 关注点：硬件供应链与芯片级后门的隐蔽性，讨论焦点是它和 rowhammer 的异同、用单个电容实现触发器的巧思以及检测难度。

关键词　hardware trojananalog malicious hardwarehardware securityrowhammer

后来怎么样

该文提出的 A2 电容触发模拟木马成为硬件安全领域的经典案例，后续大量模拟木马设计与检测研究以其为基线，推动了可信芯片与代工安全讨论。

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这几条评论里：支持 1　补充 1　亲历 1

补充将 A2 与 rowhammer 对比，强调这是故意设计且可启发更隐蔽的电源管理类攻击。

这与 rowhammer 漏洞有些相似。在 rowhammer 中，如果以特定方式反复访问某些 DRAM 芯片，一些数字元件不再按理想方式工作，本不该连接的部分出现交叉耦合，从而能修改无权访问的 RAM。但那是意外而非设计出来的。这个新攻击是故意的、非常明确，连接到保护模式位。它指向更隐蔽的攻击，比如在电源管理把 CPU 某部分开启或关闭时轻微出错；也许在某处稍微增加电容，使核心退出省电后的最初几个周期里，某些保护硬件不能正常工作。

Animats查看英文原文

This has some similarity to the rowhammer vulnerability. There, if you access some DRAM chips repeatedly in a specific way, some digital elements no longer behave in the idealized way that's expected, and there's cross-coupling between things that aren't supposed to be connected. This allows changing RAM to which you don't have access. That was accidental, rather than being designed in. This new attack is deliberate, rather than accidental, and very explicit, being wired to to the protected-mode bit. It points the way to even more subtle attacks, perhaps something that misbehaves slightly as power management is bringing some part of the CPU up or down. Maybe slightly more capacitance somewhere, so that right after a core comes out of power save, for the first few cycles some part of the protection hardware doesn't work right.

支持核心创新是用电容作计数器，降低恶意触发电路硬件成本。

这篇论文很巧妙。制造恶意电路的一个难点是，你希望行为只在某种不太可能的条件触发。也就是说你想要 if (counter == 0x686e686e) { do evil } else counter++; 但这需要大量硬件。作者意识到，本质上一个简单电容就能当计数器：每次达到条件时给电容加一点电荷，直到适当时刻放电并以某种方式改变芯片状态。这是非常聪明的设计，用单个电容实现通用且恶意的功能。

moyix查看英文原文

This is a neat paper. One of the tricky parts of making a malicious circuit is the fact that you want your behavior to only be triggered on some unlikely condition. In other words you want: if (counter == 0x686e686e) { do evil } else counter++; But that requires a lot of hardware. What the authors realized is that essentially a simple capacitor can be used as a counter! Each time you reach the condition it adds a bit of charge to the capacitor, until at the appropriate moment it discharges and changes the state of the chip in some way. This is a really clever bit of design, getting something general-purpose and malicious out of a single capacitor!

亲历读者补充作者所在 MICL，并询问论文与 Ken Thompson 信任后门论述的关联。

谢谢，我把它加入 Zotero 待读。不过我看不出这和 Ken Thompson 有什么关系。他是认为未来可能实现无法检测的硬件后门，还是什么？我今年申请了 UMich 博士，希望进入 Dennis Sylvester 教授共同作者的 MICL 实验室，但被拒了。MICL 是世界上最好的 IC 设计地点之一，Sylvester 教授非常棒。后来我拿到 GA Tech 的资助 offer，所以还好。

Cyph0n查看英文原文

Thanks for this, just added it to my Zotero backlog. I don't see what this has to do with Ken Thompson though. Did he believe that undetectable hardware backdoors would be possible in the future, or what exactly? I applied for a PhD at UMich this year hoping to work at MICL[1] under Prof. Dennis Sylvester, who co-authored this paper, but I was sadly rejected[2]. MICL is one of the best places in the world to do IC design, and Prof. Sylvester is absolutely amazing. [1]: http://www.eecs.umich.edu/micl/ [2]: I got a funded offer at GA Tech, so it's all good :D

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