I need to create a nested message in OpenPGP (my understanding is that the protocol itself should support it).
Let's say I have
Payload ("Time in Lordran is convoluted").
I do the usual PGP encryption routine with a public key
PK1, and as a result I get encrypted session key
SK1 and encrypted payload
EncPY1. I can combine this output
OUT1 as a single PGP message.
Now, I want to do the same thing again: encrypt
OUT1 but with public key
PK2 to get
OUT2. The problem here is that
OUT1 is going to generate a
Literal data packet instead of
Symmetrically Encrypted Data Packet.
It means that to retrieve the
Payload, the decryption of
OUT2 by GnuPG will happen in two passes (
gpg -d OUT2.gpg | gpg -d) instead of one (
gpg -d OUT2.gpg).
Excerpt from the RFC that confirms theoretical possibility:
The Symmetrically Encrypted Data packet contains data encrypted with a symmetric-key algorithm. When it has been decrypted, it contains other packets (usually a literal data packet or compressed data packet, but in theory other Symmetrically Encrypted Data packets or sequences of packets that form whole OpenPGP messages).
I have tried OpenPGP implementation in Go and there is no API to facilitate what I need. I would like to know if there is a library in Java, Python or any other language that fits my use case.
So far I haven't seen anyone in the libraries that I looked at that has tested creation of nested messages (except for compression).