On Mar 4, 2010, at 4:34 PM, Nicolas Boullis wrote: > Hi, > > Some time ago, I decided to revoke my old ElGamal encryption key and > replace it with a new RSA one, that I keep stored on a smartcard. (The > goal is to be ale to decrypt some messages/files with my laptop, but not > have my keys compromised if it gets lost/stolen.) > > The trouble is that I have a bunch of old messages/files, encrypted fr > my old ElGamal key: I can't decrypt them on my laptop usig my smartcard. > > So now, on a machine that has my old ElGamal secret key, I'd like to > modify those messages/files to make it possible to decrypt them using my > new RSA key. > > I don't like the naive solution "gpg --decrypt | gpg --encrypt" because: > - I would lose the signatures of messages/files that are both encrypted > and signed, > - it requires to decrypt/encrypt the whole data whie it should be > sufficient to decrypt/encrypt the session key. > > Reading RFC 4880 (OpenPGP standard), if I am able to decrypt the session > key, it should be possible to create a new Public-Key Encrypted Session > Key packet to allow a new key to decrypt the file/message. Removing a > Public-Key Encrypted Session Key should also be trivial.
Yes. > Does gnupg allow such manipulations? No. > Or does anyone have suggestions how I should implement this? Libraries > to use? You might be able to hack something together using the GnuPG sources. Certainly all of the parts you need are in there - you'd just have to put them together. Alternately, take a look at http://openpgp.nominet.org.uk/cgi-bin/trac.cgi for a library that you might also borrow some code from. David _______________________________________________ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
