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

[Kyle Moffett <mrmacman_g4@mac.com>]

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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