[12444] in cryptography@c2.net mail archive
Re: question about rsa encryption
daemon@ATHENA.MIT.EDU (Pete Chown)
Tue Feb 4 10:10:38 2003
X-Original-To: cryptography@wasabisystems.com
X-Original-To: cryptography@wasabisystems.com
Date: Tue, 04 Feb 2003 10:08:33 +0000
From: Pete Chown <Pete.Chown@skygate.co.uk>
To: cryptography@wasabisystems.com
In-Reply-To: <3E3EC816.67907732@bstormnetworks.com>
Scott G. Kelly wrote:
> I seem to recall reading somewhere that there is some issue with
> directly encrypting data with an RSA public key, perhaps some
> vulnerability, but I can't find any reference after a cursory look.
There are a few different ones, some simple and some complex. First of
all, imagine encrypting 0 or 1. Encryption leaves these numbers
unchanged. Now, if each possible plaintext had equal probability, this
would be extremely unlikely. However, in practice it is likely that
users may want to encrypt small numbers.
Another problem is that RSA encryptions multiply. If r(x) is the
encryption operation, then r(x) r(y) = r(xy). Informally:
r(x) r(y) = (x ** e) (y ** e)
= x * x * x * ... * y * y * y
= xy * xy * ... * xy
= (xy) ** e
= r(xy)
I think there are a few others too...
--
Pete
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