Messages in this thread |  | | Date | Wed, 26 Sep 2001 15:55:22 -0700 | From | Gordon Oliver <> | Subject | Re: [PATCH][RFC] Allow net devices to contribute to /dev/random |
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Hi, I would actually suggest breaking out a longer discussion of the risks associated with the patch into Documentation, and _strongly_ suggesting that the person configuring the kernel read it before enabling the option. Then a statement that this may put the security of /dev/random at risk would probably be enough.
So let's start with the possible conditions are. What I can see are the following: 1) network card on visible net: - BadGuy can monitor the network traffic, extracting timing information. Given enough knowledge about the latency of the network card, all network entropy might be known (making it non-secure). If the network is the only, or primary, source of entropy this leads to compromise 2) network card on private net: - BadGuy must plug into private net to monitor the traffic, any external monitoring is very likely to fail to get much useful information. 3) TSC not used to add randomness: - Prediction of time between interrupts becomes much easier (jiffies are a big target). 4) Systems that are largely quiescent could lead to easier prediction of latencies, and thus easier compromise.
In any case the following must be true for this to cause problems: a) The network must be the primary source of entropy (this will be common in the case where the patch is useful) b) BadGuy must monitor from time 0 (boot of system) to get useful information c) BadGuy must have information about what network card the system has, or _very_ good statistical information about delay to interrupt & timing in general. d) BadGuy must have information about how long the processing for the interrupt handler takes, as the randomness addition is done _after_ all processing. This also causes interesting problems for prediction if more than one event is handled at once. e) BadGuy must have access to information of network traffic on all the networks that are attached to the computer.
Now none of this guarantees security (but then again, very little will _guarantee_ security.
I may have missed some stuff here... (caveat emptor)
Just as a comment, I actually like the patch, and would certainly be willing to use it for a computer on a private network... -gordo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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