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SubjectRe: [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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