Re: Does OTP need authentication?

From: Tom St Denis (tomstdenis_at_iahu.ca)
Date: 12/14/03 

Date: Sat, 13 Dec 2003 23:33:35 GMT

"David Wagner" <daw@taverner.cs.berkeley.edu> wrote in message
news:brg7d6$1uqv$2@agate.berkeley.edu...
> Markus Jansson wrote:
> >Make a SHA-1 checksum of the data and store it at the end of the message
> >that is to be encrypted with OTP. Then recipient decrypts the message,
> >calculates the checksum and compares it to the checksum that came inside
> >the message and see if they are identical. Voila!
>
> Only one problem: it's not secure.
>
> (Think about known-plaintext attacks, for instance.)

Um? So you will know the hash? So what? You can't find a collision for
that pre-image you can impostor the message.

Tom

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