ElGamal: key length vs performance

David Shaw dshaw at jabberwocky.com
Sun Apr 2 00:53:15 CEST 2006

On Sat, Apr 01, 2006 at 02:12:42PM -0500, feitao wrote:
> Hi,
> As I understand, by default, GunPG uses ElGamal to encrypt/decrypt files,
> and the recommended key length is 1024 bit. Is there any information on how
> encryption/decryption time changes with the key length? Thanks a lot,

Not significantly.  GnuPG uses Elgamal to encrypt a session key, which
is only around 16-32 bytes long.  That's not going to change much
regardless of the key length.  If you were encrypting many files over
and over again, perhaps, but most people never notice it in practice.

The performance between different ciphers (3DES, AES, CAST5, etc) is
where you might see something, and it will vary over different sized
files to encrypt.


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