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rpgp / rpgp

OpenPGP implemented in pure Rust, permissively licensed
https://docs.rs/pgp
Apache License 2.0
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API to generate new subkeys #408

Open link2xt opened 1 month ago

link2xt commented 1 month ago

I want to generate a new encryption subkey for existing key.

But it seems subkey generation is only implemented in the function that generates a whole new secret key: https://github.com/rpgp/rpgp/blob/6e51094fbee39d3a33020d8e3a5ee74b5de03d2a/src/composed/key/builder.rs#L215-L248

Would be nice to factor it out to have a way to generate a new subkey.

As for subkey deletion, seems I can directly delete them from https://docs.rs/pgp/0.13.2/pgp/composed/signed_key/struct.SignedSecretKey.html because secret_subkeys field is public. For unsigned key these fields are however private, which seems inconsistent: https://docs.rs/pgp/0.13.2/pgp/composed/key/struct.SecretKey.html

hko-s commented 1 month ago

Right, subkey generation would be a good mid-level API to have, and should be easy enough to do. I'm happy to look into that, soon.

About subkey deletion, there are two different semantics one could want, when thinking about "getting rid of subkeys":

  1. signaling to others that this subkey should not be used anymore (e.g.: they should not send messages to me that are encrypted to that subkey)
  2. just not sending that subkey anymore, without signaling anything about it to correspondents

For 1, the subkey should be revoked (by issuing a new self-signature that sets the subkey metadata to "revoked"), and still sent to correspondents.

For 2, removing the subkey from the secret_subkeys field works. However, depending on the OpenPGP software of one's correspondent, it is expected that they still consider the "removed" subkey as existent and valid. Many OpenPGP libraries will continue to encrypt to a subkey that has been "removed" in this way, forever.