In AOSP Mail client, importing keys or decrypting messages attached to emails does not work. The AOSP Mail application tries to decode an attached OpenPGP messages/key (ASCII Armored -> Base64 encoding, more precisely Radix64, see RFC4880) as content, which is wrong and cripples the attachment completely. It makes no difference if the attached .asc file is directly shared to OpenKeychain or saved before opening it. The files are crippled: They end after some bytes with the string "There was an error while decoding the message." (This is actually part of the downloaded/shared file).
Send an email with Thunderbird to yourself with a file "testkey.asc" containing for example my key from http://pool.sks-keyservers.net/pks/lookup?op=get&search=0x718C070100012282 (begin copying -----BEGIN PGP PUBLIC KEY BLOCK----- to -----END PGP PUBLIC KEY BLOCK-----).
Reported upstream: https://code.google.com/p/android/issues/detail?id=75181
"There was an error while decoding the message." has been translated to german as "Beim Entschlüsseln der Nachricht ist ein Fehler aufgetreten." (https://android.googlesource.com/platform/packages/apps/Email/+/0d21834/res/values-de/strings.xml) which means: "There was an error while decrypting the message."
At best we would detect these broken files but the string message_decode_error varies between languages so it's difficult to check for it reliably.
Just a note for later:
Check if Intent data uri contains "com.android.email.attachmentprovider", if yes: Show notify that redirects to this issue.
enable view intent with text/plain (related #290)
fail with warning if we get data from the AOSP mail client (see #290)
FYI: the otherwise not that great HTC Mail client can properly save the .asc file which you can then decrypt manually. But K9 cannot show the resulting multipart file so you are then stuck with viewing in a text editor or manually extracting the HTML.
EDIT: using an IMAP account
The upcoming version has basic MIME parsing included, so the parts can then be viewed in OpenKeychain, no more manual extraction necessary 👍
The underlying problem here still remains unsolved, unfortunately.
Wow, good news. Thanks for the hard work.
Great! Does this means that there is hope to see open keychain integrated in aosp mail client one day?