OFB-based MAC

Hi

I guess the following is known in the arts but I failed to find any
papers, articles or anything about it at citeseer, google groups or
wikipedia. I even didn't find out how this is called. Perhaps someone
can give me a hint.

Given some block cipher in OFB mode I want to add authentication by
appending a cryptographic hash h over the message m before xoring the
whole with the keystream k:
c = (m, h(m)) XOR k

For me it sounds reasonable that the encrypted hash forms a MAC as it is
very unlikely that on the receiver's side the decrypted hash matches if an
arbitrary key stream was used for encrypting.

Nevertheless I could not find any work on this idea. All I did find is:
---8<---
Newsgroups: sci.crypt
Subject: Re: attack on MAC using OFB
Date: 15 Jan 2003 19:58:55 -0800
Message-ID: <1a517b5.0301151958.27e81df2@xxxxxxxxxxxxxxxxxx>
[...]
There is no standard construction for building a MAC from OFB-Mode.
[...]
--->8---

Is this still right? If so, why? Is this method perhaps broken or
braindead or somethin?

Thanks in advance

regards

Alex
.

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