[147098] in cryptography@c2.net mail archive
Re: [Cryptography] Finding Entropy Isn't That Hard
daemon@ATHENA.MIT.EDU (Marcus Leech)
Fri Sep 13 12:39:59 2013
X-Original-To: cryptography@metzdowd.com
Date: Fri, 13 Sep 2013 15:59:12 +0000 (UTC)
From: Marcus Leech <mleech@ripnet.com>
To: kentborg@borg.org
Cc: cryptography@metzdowd.com
Errors-To: cryptography-bounces+crypto.discuss=bloom-picayune.mit.edu@metzdowd.com
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<blockquote class="email_quote" style="border-left: 2px solid #267fdb; margin: 0 0 0 1.8ex; padding-left: 1ex;"><br />[* Until Linux kernel 3.6 the person maintaining urandom was busily <br />turning off interrupts as a source of entropy, I think because he didn't <br />know how much entropy he was getting so better not to get it at all <br />(huh?). In 3.6 this was changed to use all interrupts as entropy <br />sources, which is good. This means earlier kernels aren't so <br />good--though I notice that Ubuntu's kernel has the 3.6 improvement in <br />their version of 3.2, so individual distributions will vary.]<br /><br /><br />-kb</blockquote>
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<div>I'll also observe that on new mobile platforms, there are typically a flotilla of physical-world sensors. The low-level drivers for</div>
<div> these should be contributing entropy to the pool in the kernel. At the apps layer, typically, the "raw" sensor values have been</div>
<div> filtered by application-specific algorithms, so that they're less useful as entropy sources at that level.</div>
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<div>For example, low-G accelerometers are quite noisy -- these are typically used as multi-axis rotation sensors (they use the gravity-field orientation to sense rotation).</div>
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<div>Any physical-world sensor driver, where the sensor inherently has a bit of noise, I think has a "moral obligation" to contribute bits to the kernel entopy pool.</div>
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