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Re: Deducing key from encrypted & original data

On Tue, Dec 11, 2001 at 01:00:40AM +0100, Dries Kimpe wrote:
>  Hi, 
> this is something I've been wondering for some time now:
> Is it possible (or at least much easier) to extract the encryption key 
> if you both have the encrypted and original data?
>    Dries 
> PS. I know it isn't debian-related, but it's a good question anyway...

It's called a known-plaintext attack.  The answer depends on the
encryption scheme, but one of the properties of a good scheme is
that having a plaintext won't help you recover the key.  In fact,
this is an essential requirement for public-key cryptography,
because the enemy can generate as much encrypted+plaintext data
as they like.

...unless you are from Hollywood - in which case a good encryption
scheme is one that can be cracked by having lots of digits flash
up on the screen, and gradually have individual digits lock into
the correct key.

Andrew Bolt, Andrew.Bolt@arm.com
110 Fulbourn Road, Cambridge, CB1 9NJ, ENGLAND, +44 1223 400650

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