GnuPG has trouble decrypting multi-key messages?

David Shaw
Tue Feb 12 07:20:02 2002

On Tue, Feb 12, 2002 at 12:03:15AM -0500, Peter Constantinidis wrote:

> My question is, if I receive a message from someone who encrypted it with
> two formats of key, shouldn't GnuPG be smart enough to recognize that one
> of the keys is an ELG-E key and thus doesn't require me to find and install
> an IDEA.dll ? Or did I misunderstand something somewhere?

It is not true that a message encrypted with an ELG-E key
automatically won't need IDEA.  In fact, the symmetric cipher for a
given message is mostly unrelated to the algorithms for the public
keys used to encrypt.

When a message is encrypted, it is encrypted using some symmetric
cipher (of which IDEA is one of several possibilities) using a
randomly generated session key.  Then, the session key is encrypted
using the various public keys of the receipients of the message.

If the message you received used IDEA as the symmetric cipher, then
you will need the IDEA plugin regardless of what algorithm the public
keys it is encrypted to uses.


   David Shaw  |  |  WWW
   "There are two major products that come out of Berkeley: LSD and UNIX.
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