bugmonotone - Bugs: bug #8928, .mt-nonce uses way too many bits

 
 

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bug #8928: .mt-nonce uses way too many bits

Submitted by:  Nathaniel Smith <njs>
Submitted on:  Thu 13 May 2004 06:47:27 AM UTC  
 
Category: cryptographySeverity: 3 - Normal
Item Group: incorrect behaviorStatus: Fixed
Privacy: PublicAssigned to: None
Open/Closed: Closed
mtn version --full: 

Sat 31 Jul 2004 08:18:57 PM UTC, comment #1:

nonce stuff has been retired, and good riddance.

graydon hoare <graydon>
Project Member
Thu 13 May 2004 06:47:27 AM UTC, original submission:

.mt-nonce currently uses 4096 random bytes, = 32768 random bits. This is completely crazy. I'm not sure if the AutoSeededRandomPool that they're pulled from is providing pure system entropy or just seeding itself with such, but it's crazy in either case.

If it's using pure system entropy, then it's wasting at least two orders of magnitude more than it should be. 128 bits is more than sufficient to ensure uniqueness; we're currently using 256 times that. I can see going with 160 bits for consistency with the SHA1's used everywhere else, but more than that is just wasting an extremely valuable resource.

If it's not using pure system entropy, but rather doing the normally sensible thing of using a few hundred bits of real entropy to seed a secure PRNG, then we're not wasting a valuable resource, but we are being absurd. A secure PRNG is good for providing unguessable bits; if it's impossible to guess the finite input bits, then it's also impossible to guess the infinite output bits. But for collision resistance? If your seed is n bits, you only have 2^n distinct outputs, no matter how bits you read. So you might as well skip the PRNG and use the seed bits directly.

Nathaniel Smith <njs>
Project Member

 

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Follow 2 latest changes.

Date Changed By Updated Field Previous Value => Replaced By
Sat 31 Jul 2004 08:18:57 PM UTCgraydonStatusNone=>Fixed
  Open/ClosedOpen=>Closed

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