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diff --git a/posts/hsm-basics/index.html b/posts/hsm-basics/index.html deleted file mode 100644 index 0cda095..0000000 --- a/posts/hsm-basics/index.html +++ /dev/null @@ -1,278 +0,0 @@ -<!DOCTYPE html> -<html lang="en-us"> - <head> - <meta charset="utf-8"> - <meta name="viewport" content="width=device-width, initial-scale=1"> - <title>Hardware Security Module Basics | blog.jaseg.de</title> - <link rel="stylesheet" href="/css/style.css" /> - <link rel="stylesheet" href="/css/fonts.css" /> - - <header> - <nav> - <ul> - - - <li class="pull-left "> - <a href="https://blog.jaseg.de/">/home/blog.jaseg.de</a> - </li> - - - - - </ul> - </nav> -</header> - - </head> - - <body> - <br/> - -<div class="article-meta"> -<h1><span class="title">Hardware Security Module Basics</span></h1> - -<h2 class="date">2019/05/17</h2> -<p class="terms"> - - - - - -</p> -</div> - - - -<main> -<div class="document"> - - -<div class="section" id="hardware-security-modules-and-security-research-and-cryptography"> -<h2>Hardware Security Modules and Security Research and Cryptography</h2> -<p>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).</p> -<p><a class="reference external" href="mori_semi_hsm_talk_web.pdf">Click here to download a PDF with the slides for this talk.</a></p> -</div> -<div class="section" id="ideas-for-research-in-hsms"> -<h2>Ideas for research in HSMs</h2> -<p>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.</p> -<div class="section" id="the-problem-with-current-hsm-tech"> -<h3>The Problem with current HSM tech</h3> -<p>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:</p> -<ol class="arabic simple"> -<li>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.</li> -<li>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.</li> -</ol> -</div> -<div class="section" id="attacking-cost-of-implementation"> -<h3>Attacking cost of implementation</h3> -<p>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.</p> -<p>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.</p> -</div> -<div class="section" id="benefits-of-an-academic-hsm-standard"> -<h3>Benefits of an academic HSM standard</h3> -<p>Tackling the high cost of current HSM hardware with an open-source HSM blueprint would yield -several academic advantages beyond cost reduction.</p> -<ol class="arabic simple"> -<li>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.</li> -<li>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.</li> -<li>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.</li> -<li>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.</li> -</ol> -</div> -<div class="section" id="scope-of-an-academic-hsm-standard"> -<h3>Scope of an academic HSM standard</h3> -<p>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 <strong>base</strong> containing infrastructure such as the surveillance microcontroller, power supplies, -power supply filtering and hardware DPA countermeasures, and possibly a standardized mechanical and electrical -interface.</p> -<p>Next to the base, a system integrator would put their <em>payload</em>. 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 <em>payload</em> open like this achieves two benefits: It gives the HSM -blueprint's user <em>their</em> familiar tooling and the hardware <em>they</em> 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 <em>payload</em> 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 <em>payload</em> open allows research -to concentrate on the actual point, the HSM design.</p> -<p>The final and most important component would be a set of <em>security measures</em> that can be combined with the base to -form the final HSM. Each of these <em>security measures</em> would entail a detailed specification of its design, manufacture -and security properties. These <em>security measures</em> could be simple things like tamper switches or potting, but could -also be complex things like security meshes.</p> -<p>Given these three components -- <em>base</em>, <em>payload</em> and <em>security measures</em> 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.</p> -</div> -</div> -<div class="section" id="research-ideas-for-tamper-detection-mechanisms"> -<h2>Research ideas for tamper detection mechanisms</h2> -<p>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.</p> -<div class="section" id="diy-or-small-lab-mesh-production"> -<h3>DIY or small lab mesh production</h3> -<p><strong>Analog sensing</strong> 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, <a class="reference external" href="https://tches.iacr.org/index.php/TCHES/article/view/7334">Immler et al. published -a paper</a> 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 <a class="reference external" href="https://en.wikipedia.org/wiki/Physical_unclonable_function">Physically Unclonable Function, or PUF</a>. 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.</p> -<p>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.</p> -<p><strong>3D metal patterning techniques</strong> 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 -<a class="reference external" href="https://www.youtube.com/watch?v=Z228xymQYho">Ben Kraznow</a> on this exact thing.</p> -<p><strong>Copper filament methods</strong> 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.</p> -</div> -<div class="section" id="envelope-measurement"> -<h3>Envelope measurement</h3> -<p>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 <em>envelope -measurement</em> here.</p> -<p>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.</p> -<p><strong>Ultrasonic</strong> 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.</p> -<p><strong>Light</strong> 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.</p> -<p><strong>Radar</strong> 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.</p> -<p>Overall in the author's opinion these three techniques are most promising in order <em>Light</em>, <em>Ultrasonic</em>, <em>Radar</em>. 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.</p> -</div> -</div> -</div> -</main> - - <footer> - -<script> -(function() { - function center_el(tagName) { - var tags = document.getElementsByTagName(tagName), i, tag; - for (i = 0; i < tags.length; i++) { - tag = tags[i]; - var parent = tag.parentElement; - - if (parent.childNodes.length === 1) { - - if (parent.nodeName === 'A') { - parent = parent.parentElement; - if (parent.childNodes.length != 1) continue; - } - if (parent.nodeName === 'P') parent.style.textAlign = 'center'; - } - } - } - var tagNames = ['img', 'embed', 'object']; - for (var i = 0; i < tagNames.length; i++) { - center_el(tagNames[i]); - } -})(); -</script> - - - <div id="license-info"> - ©2020 by Jan Götte. 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