Re: [PATCH 7/14] random: Remove SA_SAMPLE_RANDOM from network drivers

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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.

Cheers,
Kyle Moffett


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