Re: Encryption size

From: Lassi Hippeläinen (lahippel.at.ieee.org_at_moon.invalid)
Date: 10/30/05 

Date: Sun, 30 Oct 2005 11:00:25 +0200

Ertugrul Soeylemez wrote:

> Lassi Hippeläinen <lahippel.at.ieee.org@moon.invalid> (Sat, 29 Oct 2005
> 12:03:41 +0300):
>> RSA can be seen as a block cipher. The block size is the size of the
>> modulus, which you can choose.
>
> You can't really tell if RSA is a block cipher or not. A block is a
> fixed number of of units. If you define a unit to be a byte, then it is
> a block cipher, but you can as well define a unit to be one cleartext
> unit, which is just a large number. In that case, RSA is not a block
> cipher.

The only meaningful way to define RSA block size is the size of the modulus,
as I mentioned above. Usually it is 1024 or 2048 bits, but there is no
mathematical reason why it has to be a power of two. It's only a habit that
makes sense when data records have lengths of 2^N. Also 1536 bits is in
use.

-- Lassi

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