How about using ps -laxww as a source of randomness? Of course it would be run throug something like MD5 to get rid of the structure. This would not be good on a multi-user system because ps command may have been modified to log the person invoking it, time, and output to somewhere. But on a personal workstation that you trust, it could be a pretty good source of unpredictable data. This is not my original idea, I think it was suggested in one of the multiple precision math packages I looked at recently.
From: yanek@novavax.nova.edu (Yanek Martinson)
How about using ps -laxww as a source of randomness?
Its a rather bad source. Operations of a computer system are suprisingly low on entropy. I'd guess that, if I needed to and had enough resources, I could break such a generator without more than a few months work, and even get the system to break it semi-automatic. No one here seems to think in terms of cryptanalysis and how people do it when they come up with their schemes. Perry
In some email I received from Perry E. Metzger, Sie wrote:
From: yanek@novavax.nova.edu (Yanek Martinson)
How about using ps -laxww as a source of randomness?
Its a rather bad source. Operations of a computer system are suprisingly low on entropy. I'd guess that, if I needed to and had enough resources, I could break such a generator without more than a few months work, and even get the system to break it semi-automatic.
No one here seems to think in terms of cryptanalysis and how people do it when they come up with their schemes.
Well whenever I try to come up with some nifty crypto scheme, I always seem to think it is too easy to break if you know its being used but then I dont like doing too much 'expensive' crypting and I usually find some cheap algo which uses a more expensive one for key trading. Has anyone tried using the microsecond counter from unix as a random source ? Its obviously *not* going to be good if you want a continuous stream of random numbers, but if you need them just 'every now and then', what about it ? Something like this would be used: struct timeval tv; long rand; ... gettimeofday(&tv, NULL); rand = tv.tv_usec + tv.tv_sec; ... Very unlikely to get a duplicate, esp. if you dont need the number more often than 1 per second. darren
In some email I received from Yanek Martinson, Sie wrote:
gettimeofday(&tv, NULL); rand = tv.tv_usec + tv.tv_sec;
Someone trying to break your code could find out approximately when the number was generated, then they would have a much smaller search space to try.
Thats why you change key 'regularly'...even randomly ? Then they have to 'guess' when you change keys. It might be easy to tell when an application starts, but how can you tell exactly or even approximately how long ago someone picked a menu that changed their key or it was otherwise changed ? By using the microsecound counted as a random number, its almost completely random unless you take steps to actually make less so. But a table of the required million entries and 'init' strings wouldn't be too hard for todays computers, hence the use of the time in seconds to 'bump' the offset a bit. For example, if you use a simple xor table for encoding/decoding, its pretty easy to decode. If you change the table after it has been used, every time, then the required time to break the entire message is significantly larger than it would otherwise have been. Can anyone do some maths on exactly how long it would take given a fixed table size (contains random data) ? And also with key/ table changes at a fixed/random interval ? (seems 1:1 :( but I maybe wrong). darren
From: avalon@coombs.anu.edu.au (Darren Reed) Date: Wed, 16 Dec 92 2:30:49 EST Has anyone tried using the microsecond counter from unix as a random source ? Its obviously *not* going to be good if you want a continuous stream of random numbers, but if you need them just 'every now and then', what about it ? This should be in an FAQ: Unixes have different levels of granularity in the microsecond counter; some systems may only have a 10 ms (that's 10000 microsecond) resolution to their clock. So you can't necessarily depend on a getting lot of bits of randomness from this method. - Ted
Don Davis, of MIT Project Athena, did some research a number of years back on getting good (physical) randomness out of a unix workstation. If I recall correctly, the general idea was to look for trends and biases, find explanations for them, and then filter them out or normalize against them. Sources of "real" nondeterminism came from things like variations in hard drive behavior (such as actual seek time, which shows up indirectly in the paging system because it does or does not cause time delays due to missed sectors...) I don't have a reference handy, but if noone comes up with one I'll send him email and see if he has it online. In other words, 'ps -laxww' itself is relatively useless -- but the underlying data does actually have randomness; you may have to dig pretty hard for it, though. _Mark_ SUB: Re: ps -laxww for randmoness? SUM: <tytso>, tytso (Theodore Ts'o)->avalon@coombs.anu.edu.au, cypherpunks@toad.com From: avalon@coombs.anu.edu.au (Darren Reed) Date: Wed, 16 Dec 92 2:30:49 EST Has anyone tried using the microsecond counter from unix as a random source ? Its obviously *not* going to be good if you want a continuous stream of random numbers, but if you need them just 'every now and then', what about it ? This should be in an FAQ: Unixes have different levels of granularity in the microsecond counter; some systems may only have a 10 ms (that's 10000 microsecond) resolution to their clock. So you can't necessarily depend on a getting lot of bits of randomness from this method. - Ted
participants (5)
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avalon＠coombs.anu.edu.au -
Mark W. Eichin -
pmetzger＠shearson.com -
tytso＠ATHENA.MIT.EDU -
yanek＠novavax.nova.edu