Hi,

I'm pleased to report that I've just added support for decrypting SEIP packets as well as verifying MDC packets to Sequoia. See:

https://gitlab.com/sequoia-pgp/sequoia/commit/e304deb0fc7a92801cf3ba58aafeb1...

Currently, there is only a low-level interface. The basic usage is more or less shown in the decryption unit test:

https://gitlab.com/sequoia-pgp/sequoia/blob/e304deb0fc7a92801cf3ba58aafeb14c...

Basically, we create a packet parser as usual:

let mut pp = PacketParserBuilder::from_file(&path).unwrap() .buffer_unread_content() .finalize() .expect(&format!("Error reading {}", filename)[..]) .expect("Empty message");

Then, we iterate over the message, and when we encounter a SEIP packet, we decrypt it:

if let Packet::SEIP(_) = pp.packet { pp.decrypt(algo, &key[..]).unwrap(); }

Now, if we recurse on the SEIP packet (pp.recurse() instead of pp.next()), we will iterate over the decrypted packets (otherwise the decrypted data will be stored in packet.body).

When we encounter the MDC packet, we can check the hash as follows:

if let Packet::MDC(mdc) = pp.packet { assert_eq!(mdc.computed_hash, mdc.hash); }

Right now, it is up to the implementation to gather the SK-ESK and PK-ESK packets and extract the symmetric encryption algorithm and session key.

When using a Message to parse a message all a once, it is currently not possible to decrypt the SEIP packets.

Another current limitation has to do with the packet parser and not symmetric decryption per se: when a packet in the SEIP packet has an indefinite length (which is how GnuPG encodes the length of compressed data packets), Sequoia assumes that the remaining data belongs to packet with the indefinite length; if some data is unread, Sequoia just drops the data instead of looking for more packets.

If someone is looking for a small project, consider adding a decrypt command to sq.

:) Neal