automatically obtain PGP keys for e-mail recipients via keyserver
Objective
Evolution should be able to automatically retrieve the PGP keys for the recipients from keyservers. This is apparently implemented by other clients as for example in Thunderbird with Enigmail.
This enables the user to encrypt messages to recipients without the necessity to manually check if a key is publicly available. The assessment of trust to the key is a separate issue.
Additional features
Ideally the following would be possible:
- The search for keys would start in background as soon as a recipient is defined.
- In case the result of the search is ambiguous, the user is prompted which key shall be used (remember decision).
Background information
This issue may be related to #39.
Reliance on auto-key-locate
It has been suggested by @mcrha that automatic key discovery with Evolution should be working solely by setting up GnuPG correctly. This would rely on libcamel invoking gpg configured to automatically locate and retrieve keys through auto-key-locate. It has been observed that Evolution 3.22.6 specifies the recipient in a form (<local@domain>), which is not used by auto-key-locate for lookups on a keyserver. This has been confirmed with GnuPG version 2.1.18, 2.2.12 and 2.2.17.
To this day it has not definitively been settled if this behavior of GnuPG is intended or not. This is quite uncertain as different parts (see auto-key-locate and user id) of the GnuPG manual are not necessarily consistent. It is at the discretion of the GnuPG developers if or when to change the accepted forms (see bug report).
Other approaches
Certainly other solutions should be possible. For example by altering the form when libcamel is adding the recipients to the argument list. As a workaround this script can be used to circumvent the interoperability issue.
A compelling solution implementing the additional features would probably require to have several different asynchronous calls to gpg.