Messages in this thread | | | Subject | Re: predictable IP ID | From | Andi Kleen <> | Date | 06 Oct 1999 17:19:51 +0200 |
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vonbrand@inf.utfsm.cl (Horst von Brand) writes:
> Savochkin Andrey Vladimirovich <saw@msu.ru> said: > > [...] > > > Now we have a strong RND based generator for the first ID for a peer. But > > its fairly slow (MD4 hash) and can't be used for every packet. Strength of > > the generator and requirements for a guaranteed long period contradicts each > > other. > > Wasn't the /dev/random stuff invented exactly for this kind of uses? I'd > assume you can bypass the MD hash here, and just steal a byte or two > directly from the entropy pool.
First that would allow an attacker to guess the state of the entropy pool (letting him predict future /dev/urandom output yuck, cracking your session keys). Normal /dev/random uses an hash to prevent exactly that.
And you need 2 bytes (16bit) per packet. For fast or gigabit ethernet you would need several hundred KB of entropy per minute. Where you get that much entropy from?
/dev/u?random is really only good for seeding fast RNDs, not replacing them.
-Andi -- This is like TV. I don't like TV.
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