Messages in this thread | | | Date | Fri, 5 May 2006 12:24:26 -0500 | From | Matt Mackall <> | Subject | Re: [PATCH 7/14] random: Remove SA_SAMPLE_RANDOM from network drivers |
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On Fri, May 05, 2006 at 01:13:23PM -0400, Kyle Moffett wrote: > On May 5, 2006, at 12:42:35, Matt Mackall wrote: > >Remove SA_SAMPLE_RANDOM from network drivers > > > >/dev/random wants entropy sources to be both unpredictable and > >unobservable. Network devices are neither as they may be directly > >observed and controlled by an attacker. Thus SA_SAMPLE_RANDOM is > >not appropriate. > > I thought I saw an analysis somewhere of why it was actually OK to > include randomness from network devices (or even basically any > interrupt source that isn't periodic on a fundamental hardware > level). It had something to do with investigating interrupt arrival > time from real-time network traffic; they hooked a logic analyzer of > sorts up to the physical ethernet cable itself and to the system bus > of the destination computer (and wrote software that recorded a TSC > timestamp of every interrupt). Essentially the interaction between > the occasional ethernet retransmission, variable internal network > card latencies and queues, variable CPU-dependent interrupt > latencies, critical sections in the OS, etc, plus the high-resolution > nature of the TSC used for a seed value made it a chaotic system and > basically cryptographically impossible to predict the interrupt > data. It's possible that the analysis I saw was later proven > incorrect; but I'd be interested if you've seen some paper or > research on the topic that I haven't, I'd be interested in references.
I haven't seen such an analysis, scholarly or otherwise and my bias here is to lean towards the paranoid.
Assuming a machine with no TSC and an otherwise quiescent ethernet (hackers burning the midnight oil), I think most of the hard-to-analyze bits above get pretty transparent.
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