Twofish algorithm

[Jason Essington]

On Tuesday, September 25, 2001, at 12:25 PM, Smith, Jeffrey J. wrote:

> Since the Twofish appears to be incompatible between the two products,
> how do I remove the Twofish algorithm from the GnuPG preferences? Then,
> the public key sent to PGP will not hoave the Twofish algorithm as an
> option. And, is removing the Twofish algorithm the correct approach.

I have had to do this for a projet i was working on as well. the 
problem is that the preferences are hardcoded in the keygen.c 
file (there is some reference to this in one of the faq 
documents).

you will need to change the preferences in the function 
keygen_add_std_prefs then recompile then generate a new key with 
the new executable (maybe simply editing the existing key with 
the new executable will change the prefs, I can't remember). I 
do keep this executable separate from my fully functional 
executable however so that I don't mistakenly create crippled 
keys when I don't intend to.

at any rate the part you are looking for looks like this:

           buf[0] = CIPHER_ALGO_RIJNDAEL;
           buf[1] = CIPHER_ALGO_TWOFISH;
           buf[2] = CIPHER_ALGO_CAST5;
           buf[3] = CIPHER_ALGO_BLOWFISH;
                build_sig_subpkt( sig, SIGSUBPKT_PREF_SYM, buf, 4 );

you probably want to change it to something like this to remove twofish:

           buf[0] = CIPHER_ALGO_RIJNDAEL;
           buf[1] = CIPHER_ALGO_CAST5;
           buf[2] = CIPHER_ALGO_BLOWFISH;
                build_sig_subpkt( sig, SIGSUBPKT_PREF_SYM, buf, 3 );

I think, however, there was some talk of adding a way to change 
the preferences from gpg without having to recompile and 
recreate the key? Werner?

Jason Essington