Re: Question on Symmetric encryptions algorithms:

From: Henrick Hellström (henrick.hellstrm_at_telia.com)
Date: 06/28/03 

Date: Sat, 28 Jun 2003 00:11:18 GMT

Shashank Khanvilkar wrote:
> Is it possible that a symetric encryption algorithm (aes-128-cbc, say) can
> actually produce an encrypted output file which is smaller in size than the
> original input file.
> Will appreciate any help.

No, that is not possible, but:

1) it is not unusual that crypto software compress the input before
encryption, and
2) primitives such as AES might be used for other purposes than
encryption, e.g. for message authentication (AES-CBC-MAC) or hashing
(e.g. the DES-based unix password hash) and the output of such
constructs is usually the size of a single block.