GPG with SMP?

David Tomaschik david at
Wed Oct 5 19:29:09 CEST 2011

On Wed, Oct 5, 2011 at 1:09 PM, Robert J. Hansen <rjh at> wrote:
> On 10/5/11 11:01 AM, Thomas Harning Jr. wrote:
>> Mr. Hansen, thanks for the correction on CTAK, made me re-look into the
>> specific details of CTAK... whoops.  Should have taken a look at the
>> OpenPGP specification and noticed that CFB is what is used for all
>> symmetric encryption.
> Goofs happen, man.  :)
> Also, a note for anyone who's confused (what's CTAK? does GnuPG use CTAK
> or CFB for symmetric encryption? etc.): CFB stands for "Cipher
> Feedback", which is a particular mode of operation for symmetric
> ciphers.  CTAK is "Ciphertext Autokey", which is the exact same thing by
> another name.

To be pedantic, CTAK is the general concept of incorporating the
ciphertext into the keystream.  CFB is a precise way of implementing
CTAK.  PCBC also incorporates the plaintext into the input for the
encryption process, IIRC.

David Tomaschik, RHCE, LPIC-1
System Administrator/Open Source Advocate
OpenPGP: 0x5DEA789B
david at

More information about the Gnupg-users mailing list