Re: [gmime-devel] g_mime_part_get_openpgp_data () and Content-Transfer-Encoding: base64

[Jeffrey Stedfast <fejj gnome org>]

On 12/12/2017 3:48 AM, Daniel Kahn Gillmor wrote:
> hey Jeff and other GMime folks--

Hey!

> I've been working on adding support for decryption of PGP inline
> messages over on notmuch [0], but i notice that at least for some
> e-mails it seems that they are not detected.
>
> In particular, some of my contacts are sending me inline PGP encrypted
> messages through some chain of MUAs/webmail/MTAs that automagically
> base64-encode any text the human supplies.

Ugh :(

> [snup]
>
> Consequently, i think g_mime_part_get_openpgp_data returns
> GMIME_OPENPGP_DATA_NONE instead of GMIME_OPENPGP_DATA_ENCRYPTED, so my
> work for notmuch doesn't actually recognize that these parts have inline
> PGP encrypted data in them.

This makes sense... I'll explain why later.

> I'm pretty well convinced that inline PGP is a bad idea generally, so i
> don't want GMime to twist itself into knots about this.  but if there's
> some obvious fix that you see that would also catch these particular
> messages, i'd be happy to know about it.
>
> Any ideas?  is my analysis wrong somehow?

The get_openpgp_data() function returns an enum value (or bitfield? I 
can't remember atm) based on the OpenPGP markers that the GMimeParser 
found while parsing the message (while scanning for MIME boundaries). 
Since the GMimeParser does not decode the content as it is parsing the 
message, it can't peer under the obfuscation of the base64 encoded blob.

I thought this would be enough since in the subset of messages that I've 
personally seen that use inline PGP, the text always comes through using 
the 7bit (either implicitly or explicitly), 8bit, or quoted-printable 
(which makes sense for signed messages) encodings which do not obfuscate 
the OpenPGP markers. I hadn't considered the likelihood of (especially) 
encrypted messages being encoded using base64 since there's literally no 
reason to do that (armored PGP data is already 7bit clean).

There's no easy way to make this work by doing it in the parser, *but* I 
could possibly write a GMimeFilter that would be able to detect OpenPGP 
markers.

Once I do that, I could have g_mime_part_get_openpgp_data() use said 
filter if the current GMimeOpenPGPData state is NONE.

How does that sound?

Jeff