netdev - Re: [PATCH] - trivial - Improve appletalk checksum calculation

lists.openwall.net		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 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:	Mon, 22 Oct 2007 18:36:28 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Miller <davem@...emloft.net>
Cc:	acme@...stprotocols.net, netdev@...r.kernel.org
Subject: Re: [PATCH] - trivial - Improve appletalk checksum calculation

On Mon, 2007-10-22 at 17:35 -0700, David Miller wrote:
> Your code is rotating bit 15 down by one bit and bits 0-14 up by one
> bit.

Yes, a 16 bit rotate left.

There was a discussion a few years ago:
http://oss.sgi.com/archives/netdev/2003-10/msg00734.html

>>From the spec:

Implementers of DDP should treat generating the checksum as an optional
feature. The 16-bit DDP checksum is computed as follows:

CkSum := 0 ;
FOR each datagram byte starting with the byte immediately following this
Checksum field
REPEAT the following algorithm:
          CkSum := CkSum + byte; (unsigned addition)
          Rotate CkSum left one bit, rotating the
              most significant bit in least significant bit;
IF, at the end, CkSum = 0 THEN
          CkSum := $FFFF (all ones).

Reception of a datagram with CkSum equal to 0 implies that a checksum is
not performed.



-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html