Werner Koch
Wed Jun 19 11:29:01 2002

On Wed, 19 Jun 2002 10:41:59 +0200, Malte Gell said:

> Hi there,
> "modification detection code", sounds interesting, can you tell us more about 
> that ? Would be nice if you could enlighten us a bit ;-)

See the latest OpenPGP draft (draft-ietf-openpgp-rfc2440bis-05.txt).

> The man page says mdc is used for ciphers with block sizes >64 bit, so it's 
> automatically used with AES,Twofish, does it make sense to force the use of 

This behaviour is actually not defined as the OpenPGP WG decided that
we are going to use a special key flag for this (similiar to
preferences).  gpg 1.0.7 has full support for this key flag and
generates new keys with it set.  However there are only a few keys out
with support for that key, so we use a kludge to always use the MDC
feature for cipher algorithms using a blocksize different from 64 bits
which happens to be AES and Twofish. 

> mdc with --force-mdc when using 3DES or CAST5 or is mdc best used with the 
> new ciphers ?

No, DON'T DO THAT!  Older versions of GnuPG and most PGP versions
won't be able to decrypt this message.