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To: Hans Steegers <steegers,AT,steegers,DOT,nl>
Subject: Re: Data integrity check in CIPE - Please explain me thenecessityor benefit of a larger checksum.
From: "Eric M. Hopper" <hopper,AT,omnifarious,DOT,org>
Date: Mon, 29 Sep 2003 11:25:16 -0500
Cc: cipe-l,AT,inka,DOT,de
In-reply-to: <000b01c38675$53448180$d620a8c0@pcw_hans.hnsasd.priv>
Organization: Omnifarious Software
References: <000b01c38675$53448180$d620a8c0@pcw_hans.hnsasd.priv>

On Mon, 2003-09-29 at 05:34, Hans Steegers wrote:
> ** ip-packets contain a CRC-16 over the header only,
> ** tcp contains a CRC-16 over header and data + sequence / ack numbers,
> ** udp datagrams contain a CRC-16 over data and header.

They do not use CRC-16, they use a checksum.

This does make the packets harder to modify, but how much harder?  Can
you give me a specific bound on how hard it would be to modify the
packet?  Without such a specific bound, I'm forced to conservatively
assume that it's no harder than if those checksums aren't there.

Have fun (if at all possible),
--
There's an excellent C/C++/Python/Unix/Linux programmer with a wide
range of other experience and system admin skills who needs work.
Namely, me. http://www.omnifarious.org/~hopper/resume.html
-- Eric Hopper <hopper,AT,omnifarious,DOT,org>

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