Encrypting mail to mail not in address book fails

More general example below: https://github.com/k9mail/k-9/issues/2055#issuecomment-274272755

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Expected behavior

Encrypt & send mail to [e-mail].

Actual behavior

“Private key could not be found” is displayed.

Steps to reproduce

1. Add [e-mail] (3359 0391 70A3 CD9B 25CF 5A46 231A 83AF DA9C 2434) to OpenKeychain.
2. Create a mail. As you can see, the “To” indicator sees the PGP key for the mail, but the encryption indicator at the top right indicates that the mail cannot be encrypted (security slider is set to “always encrypt” here):

I suspect this is an issue with the key (as also other PGP clients failed), but depending on what this is, you might improve the UI/UX of K9 mail as the current claim (in the error message) is proven to be wrong: There is a key for this mail.

Environment

K-9 Mail version: v5.202

Android version: CM 13/Android 6

[ar-]

Hi. I put the two keys from above into 2 text files and ran gpg --with-fingerprint and gpg --list-packets on them. I attach the outputs of both files here. a_key.txt b_key.txt

You can view them in a diff viewer too see what is different.

As far as I see it: the first key was created on 2011-02-26 and the second one on 2014-07-05. The newer one (the one he emailed to you) removes an expiry date in one of the sub keys. In the older one the subkey expired on 2016-02-25. That might be the reason why it doesn’t work anymore right now?!

On the public key server http://pgp.mit.edu/pks/lookup?op=vindex&search=0x231A83AFDA9C2434 you can also see (in the last 2 lines) the removed expiry date.

And yes, both of them show the same fingerprint, since the same private key was used to sign these subkeys.

[dschuermann]

@rugk Yup, I think you are right. This should be the same as #1655