lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 23 Mar 2007 14:58:05 +0300
From:	Evgeniy Polyakov <>
To:	David Miller <>
	Eric Dumazet <>
Subject: XOR hash beauty solved [Was: RFC: Established connections hash function]

> Please, do not apply patch as is, I will devote this day to find where
> jenkins has problems and try to fix distribution. If I will fail, then
> it is up to you to decide that above results are bad or good.

I need to admit that I was partially wrong in my analysis of the Jenkins
hash distribution - it does _not_ have problems and any kind of artifacts. 
Waves found in tests are results of folding into hash_size boundary,
distribution inside F(32) field is unifirm.
XOR hash does not have such problem, because it uses (u32 ^ u16) as one
round, which results in the uniform (it is not correct to call that
distribution uniform as is, but only getting into account that u16 values 
used in tests were uniformly distributed) distribution inside F(16), which 
does not suffer from hash_size boundary folding. Since XOR hash has 3 rounds, 
only one of them (xor of the final u32 values) will suffer from folding, but 
tests where is it can be determined for sure use constant addresses, so 
problem hides again.

So, briefly saying, jhash_2/3words have safe distribution, but have
higher-number of elements waves as a result of folding which is
unavoidable for general-purpose hash.

Now my conscience is calm :)

	Evgeniy Polyakov
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists