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diff --git a/content/blog/hsm-basics/index.rst b/content/blog/hsm-basics/index.rst deleted file mode 100644 index 306edcd..0000000 --- a/content/blog/hsm-basics/index.rst +++ /dev/null @@ -1,214 +0,0 @@ ---- -title: "Hardware Security Module Basics" -date: 2019-05-17T15:29:20+08:00 ---- - -Hardware Security Modules and Security Research and Cryptography -================================================================ - -On May 17 2019 I gave a short presentation on the fundamentals of hardware security modules at the weekly seminar of -Prof. Mori's security research working group at Waseda University. The motivation for this was that outside of low-level -hardware security people and people working in the financial industry HSMs are not thought about that often. In -particular most network or systems security people would not consider them an option. Also it could turn out to be -really interesting to think about what could be done with an HSM in conjunction with modern cryptography (instead of -just plain old RSA-OAEP and AES-CBC). - -`Click here to download a PDF with the slides for this talk. <mori_semi_hsm_talk_web.pdf>`__ - -Ideas for research in HSMs -========================== - -Preparing for this talk brought me back to some research ideas I've been working on for a while now. Since I'm not sure -I'll find the time to properly research this topic, I thought it would be great to write down some rought outlines first -for future reference. - -The Problem with current HSM tech ---------------------------------- - -Currently, HSMs are only used in certain specific niche applications such as certificate authority key management and -financial transaction data handling. One key reason for this is that HSMs currently don't provide the affordances that -would be needed for them to be adopted more widely by the cryptographic and security engineering community. As far as I -can tell, the two core missing affordances are: - -1. To be more widely adopted, HSMs must become less expensive. Currently, they go for several tens of thousands of Euro, - which puts them outside most budgets. -2. To be more widely adopted, HSMs must provide the standardized programming interfaces familiar to cryptographic - developers. Currently, every HSM vendor has their own custom cryptographic API and a developer will have to train on - one specific vendor's tooling. Furthermore, any documentation of these internals is kept secret behind NDAs. This - constitutes a high barrier to entry, decreasing adoption in particular with young developers accustomed to - open-source ecosystems. - -Attacking cost of implementation --------------------------------- - -The first issue can be addressed by simply creating a viable low-cost alternative. There is no fundamental technical -reason for the high cost of HSMs. This cost is instead due to manufacturers trying to recoup their expenses for R&D as -well as certification from the small volumes HSMs are sold in. - -Compared to system integration and certification the pure R&D cost of HSM defense mechanisms themselves is not too high -in an academic context it should be feasible to develop a sort of HSM blueprint that can then be cheaply produced by -anyone in need. Since the application areas outlined here are far from the core business areas of the clients of -established HSM vendors this would most likely not be a realistic threat to any established vendor's business and a -co-existence of both should not pose any problems in the short term. - -Benefits of an academic HSM standard ------------------------------------- - -Tackling the high cost of current HSM hardware with an open-source HSM blueprint would yield -several academic advantages beyond cost reduction. - -1. An open-source blueprint could serve as an academic reference design to evaluate and compare other HSM designs - against. For instance this would not only allow quantifying the effectiveness of academic security measures but also - allow an evaluation of commercial HSMs. -2. An open-source blueprint could stimulate academic research in this academically very quiet albeit commercially - important area. This research would ultimately benefit everyone employing HSMs by raising security standards in the - field. Since HSMs are never solely relied upon for overal system security both defensive and offensive security - research would yield these benefits. -3. An open-source blueprint would encourage new people to get into the field and both apply HSMs to practical problems - as well as improve HSMs themselves. Currently, this is highly discouraged due to the strictly proprietary nature of - all available systems. -4. Finally, developing an open-source HSM blueprint might yield new findings in adjacent academic areas due to the - hightly multi-disciplinary nature of security research in general and HSM design in particular. - -Scope of an academic HSM standard ---------------------------------- - -An academic HSM blueprint would need to be flexible so that researchers can adapt it to their particular problem. A -modular architecture would lend itself to this flexibility. Fundamentally, there would be three components to this -architecture. First, a **base** containing infrastructure such as the surveillance microcontroller, power supplies, -power supply filtering and hardware DPA countermeasures, and possibly a standardized mechanical and electrical -interface. - -Next to the base, a system integrator would put their *payload*. The nature of this payload is intentionally kept -unspecified, and it might be anything from a cryptographic microcontroller to a small embedded system such as a -raspberry pi single board computer. Keeping the *payload* open like this achieves two benefits: It gives the HSM -blueprint's user *their* familiar tooling and the hardware *they* need, allowing fast adoption. Someone well-versed in -e.g. Javascript could literally implement their cryptography in Javascript, run it on an off-the-shelf raspberry pi and -just apply the HSM blueprint around it. In addition, keeping the *payload* open reduces the scope of what needs to be -implemented. Building a general SDK on top of something like a bare ARM SoC such as a TI OMAP or a Freescale/NXP IMX -would be a considerable additional burden, on top of the actual HSM design. Keeping the *payload* open allows research -to concentrate on the actual point, the HSM design. - -The final and most important component would be a set of *security measures* that can be combined with the base to -form the final HSM. Each of these *security measures* would entail a detailed specification of its design, manufacture -and security properties. These *security measures* could be simple things like tamper switches or potting, but could -also be complex things like security meshes. - -Given these three components -- *base*, *payload* and *security measures* as detailed specifications any engineer should -be able to design and manufacture a HSM customized to their needs. Unifying these three components within the HSM -blueprint would be a set of reference designs. Each reference design would implement a particular parametrization of the -three architectural components with a physical hole cut out where the payload would go.. These reference designs would -for one serve to guide any implementer on the customization and integration of their own derivation from the blueprint. -In addition it would serve as an extremely simple, low-cost point of entry into the ecosystem. A curious researcher -could simply replicate the reference design and put their existing payload inside. Practically this might mean e.g. a -researcher having PCBs produced according to the design files for a reference design for a mesh-based HSM, producing -their own mesh, physically glueing a raspberry pi SBC into the middle of it, and potting the resulting system. Given the -ease of prototype PCB fabrication today this would realistically allow evaluation of HSM technologies on a budget that -is orders of magnitude less than the cost of current HSMs. - -Research ideas for tamper detection mechanisms -============================================== - -The core component of an HSM blueprint would be a suite of tamper detection mechanisms. Following are a few ideas on how -to improve on the current state of the art of membrane tamper switches plus temperature sensors plus PCB and printed -security meshes plus potting. - -DIY or small lab mesh production --------------------------------- -**Analog sensing** meshes are a proven technology where instead of just monitoring for continuity and shorts, analog -parameters of the mesh traces such as inductance and mutual capacitance are monitored. In 2019, `Immler et al. published -a paper <https://tches.iacr.org/index.php/TCHES/article/view/7334>`__ where took this principle and turned it all the -way up. They directly derived a cryptographic secret from the analog properties of their HSM's security mesh in an -attempt to built a `Physically Unclonable Function, or PUF -<https://en.wikipedia.org/wiki/Physical_unclonable_function>`__. The idea with PUFs is that they reproduce some entropy -that comes from random tolerances of their production process. The same PUF will always yield (approximately) the same -key, but since you cannot control these random production variations, in practice the resulting PUF cannot be cloned. -Note however, that its secrets can of course be copied if you find a way to read them out. - -As Immler et al. demonstrated in their paper, you don't need any secret sauce to create an analog mesh sensing circuit. -All you need are a bunch of (admittedly, expensive) off-the-shelf analog ICs. The interesting bit here is that by -applying more advanced analog sensing, weaknesses of an otherwise coarse mesh desing could maybe be alleviated. That is, -instead of monitoring a very fine mesh for continuity, you could instead closely monitor inductance and capacitance of a -more coarse mesh. This trade-off between sensing circuit complexity (resp. cost) and mesh production capabilities may -allow someone with a poorly equipped lab to still make a decent HSM. The question is, how do you produce a "decent" mesh -given only basic tools? Here are some ideas. - -**3D metal patterning techniques** refers to any technique for producing thin, patterned metal structures on a -three-dimensional plastic substrate. The basic process would consist of 3D-printing the polymer substrate, depositing a -thin metal layer on top and then patterning this metal layer. A good starting point here would be the recent work of -`Ben Kraznow`_ on this exact thing. - -**Copper filament methods** would be any method embedding copper wire from a spool in some resin or other matrix. This -could mean either of a systematic approach of carefully winding or folding the copper wire into patterns or a -non-systematic approach of simply stuffing a large tangle of copper wire into a small space. The main challenge with the -former would be to find a non-tedious way of production. The main challenge with the latter would be to find process -parameters that guarantee complete coverage of the HSM without holes or other areas of lower sensitivity to intrusions. -Both approaches would require careful consideration of the overall design including the polymer resin supporting -structure to ensure sensitivity against attacks since copper wire is mechanically much stronger than the micrometre-thin -metal coatings used in patterning techniques. - -Envelope measurement --------------------- - -Finally, I think there is another set of currently under-utilized tamper-detection methods that would be very -interesting to explore. I am not aware of an academic term for these, so I am just going to dub them *envelope -measurement* here. - -The fundamental apporach of a mesh is to build a physical security envelope (the mesh) that physically detects when it -is disturbed (open or short circuits). This approach works well but has the disadvantage that these meshes are rather -complex to manufacture since effectively every part of them is acting as a sensing element. A conceptually more complex -but in practice potentially simpler approach might be to split the functions of security envelope and sensing element. -This would mean that in place of the mesh, some form of passive element such as metal foil forms the security envelope -which is then checked for tampering using a very sensitive sensor inside. This remote-sensing approach might simplify -the manufacture of the envelope itself and thus yield a design that is more easily customized. Following are a few ideas -on how to approach this envelope measurement problem. - -**Ultrasonic** If the HSM is potted, a few ultrasonic transducers could be added inside the potting. With several -transducers, any one could be used to transmit ultrasound while the others measure complex phase and energy of the -signal they receive. The circuitry for this could be made fairly simple if using a static transmit frequency or a low -chirp rate by using a homodyne receiver built around a comparator fed into some timers. This approach would likely -detect any mechanical attack and would also rule out chemical attacks involving liquids (though starting from which -amount of liquid depends on receiver sensitivity). The main disadvantages might be high power consumption and cost and -size of the ultrasonic transducers. Traditional cheap transducers made for air as a transmission medium are fairly large -and might not adequately couple into potting compound. If somehow one could convince a standard small piezo element to -do the same job that would be great as far as cost and size are concerned. A concern in some fringe use cases might be -suceptibility to ambient noise, though this could easily be reduced at the expense of space and heat dissipation -capacity by adding sound dampening on the outside. A likely attack vector against this approach might be using a laser -cutter to drill a hole through the potting compound, then inserting probes carefully chosen to not couple too much -to the potting compound ultrasonically. - -**Light** In either an unpotted HSM or one potted with a transparent (at some wavelengths) potting compound one could -embed LEDs and photodiodes in a similar setup to the ultrasonic setup described above. In contrast to the ultrasound, -the LEDs would literally have to light up the HSM's interior and shadows might be an issue since the HSM is likely some -flat rectangular shape. A possible solution to this would be to coat both the embedded payload and the lid with some -highly reflective paint such as some glossy silver paint or simple white paint. The basic approach might be as simple as -simply turning on several LEDs distributed throughout the HSM in turn and measuring amplitude at several photodetectors, -or as complex as doing a LIDAR-like phase measurement sweeping through a range of frequencies to determine not only -absorption but also phase/distance characteristics between emitter LED and detector photodiode. Using some high-gain TIA -along with a homodyne detector (lock-in amplifier) and changing emitter intensity, very precise measurements of both -absorption and phase might be possible, as might be measurements through almost opaque, diffuse potting compounds such -as a grey epoxide resin. The main disadvantages of this method would likely be the need to thoroughly light-proof the -entire HSM (likely by wrapping it in metal foil) and the potentially high cost of transmitter and receiver circuitry -(nice TIAs aren't cheap). To be effective against attacks using e.g. very fine drills and probes the system would likely -have to be very sensitive. - -**Radar** Finally, one could turn to standard radar techniques to fingerprint the inside of the HSM. The goal here would -be fingerprinting instead of mapping since only changes need to be detected. In this approach one could use homodyne -detection to improve sensitivity and reduce receiver complexity, and sweep frequencies similar to an FMCW radar (but -probably without exploiting the self-demodulation effect). Besides high cost, this approach has two disadvantages. -First, such a system would likely not go beyond 24GHz or maybe 40GHz due to component availability issues. Even at 40GHz -the wavelength in the potting compound would be in the order of magnitude of several millimeters. Fine intrusions using -some tool chosen to not interact too much with the EM field inside the HSM such as a heated ceramic needle or simply a -laser cutter might not be detectable using this approach. In any case, this system would certainly not be able to detect -small holes piercing the HSM enclosure. The HSM enclosure would have to be made into an RF shield, likely by using some -metal foil in it. - -Overall in the author's opinion these three techniques are most promising in order *Light*, *Ultrasonic*, *Radar*. Light -would prbably provide the best sensitivity at expense of some cost. Ultrasonic might be used in conjunction with light -to cover some additional angles since it is potentially very low-cost. Radar seems hard to engineer into a solution that -works reliably and also would likely be at least an order of magnitude more expensive than the other two technologies -while not providing better sensitivity. - -.. _`Ben Kraznow`: https://www.youtube.com/watch?v=Z228xymQYho -.. _affordances: https://en.wikipedia.org/wiki/Affordance - |