Enigmail generates a "legacy-display" part when it sends encrypted
mail with a protected Subject: header. This part is intended to
display the Subject for mail user agents that are capable of
decryption, but do not know how to deal with embedded protected
headers.
This part is the first child of a two-part multipart/mixed
cryptographic payload within a cryptographic envelope that includes
encryption (that is, it is not just a cleartext signed message). It
uses Content-Type: text/rfc822-headers.
That is:
A └┬╴multipart/encrypted
B ├─╴application/pgp-encrypted
C └┬╴application/octet-stream
* ╤ <decryption>
D └┬╴multipart/mixed; protected-headers=v1 (cryptographic payload)
E ├─╴text/rfc822-headers; protected-headers=v1 (legacy-display part)
F └─╴… (actual message body)
In discussions with jrollins, i've come to the conclusion that a
legacy-display part should be stripped entirely from "notmuch show"
and "notmuch reply" now that these tools can understand and interpret
protected headers.
You can tell when a message part is a protected header part this way:
* is the payload (D) multipart/mixed with exactly two children?
* is its first child (E) Content-Type: text/rfc822-headers?
* does the first child (E) have the property protected-headers=v1?
* do all the headers in the body of the first child (E) match
the protected headers in the payload part (D) itself?
If this is the case, and we already know how to deal with the
protected header, then there is no reason to try to render the
legacy-display part itself for the user.
Furthermore, when indexing, if we are indexing properly, we should
avoid indexing the text in E as part of the message body.
'notmuch reply' is an interesting case: the standard use of 'notmuch
reply' will end up omitting all mention of protected Subject:.
The right fix is for the replying MUA to be able to protect its
headers, and for it to set them appropriately based on headers found
in the original message.
If a replying MUA is unable to protect headers, but still wants the
user to be able to see the original header, a replying MUA that
notices that the original message's subject differs from the proposed
reply subject may choose to include the original's subject in the
quoted/attributed text. (this would be a stopgap measure; it's not
even clear that there is user demand for it)
This test suite change indicates what we want to happen for this case
(the tests are currently broken), and includes three additional TODO
suggestions of subtle cases for anyone who wants to flesh out the test
suite even further. (i believe all these cases should be already
fixed by the rest of this series, but haven't had time to write the
tests for the unusual cases)
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Protected subject lines were being emitted in reply when the cleartext
of documents was indexed. create_reply_message() was pulling the
subject line from the index, rather than pulling it from the
GMimeMessage object that it already has on hand.
This one-line fix to notmuch-reply.c solves that problem, and doesn't
cause any additional tests to fail.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
These tests are currently broken! When a protected subject is indexed
in the clear, it leaks in the reply headers :(
For emacs, we set up separate tests for when the protected header is
indexed in the clear and when it is unindexed. neither case should
leak, but the former wasn't tested yet.
We will fix the two broken tests in a subsequent patch.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
We want to make sure that internally-forwarded messages don't end up
"bubbling up" when they aren't actually the cryptographic payload.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
This test scans for all the possible protected headers (including
bogus/broken ones) that are present in the protected-headers corpus,
trying to make sure that only the ones that are not broken or
malformed show up in a search after re-indexing.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Up to this point, we've tested protected headers on messages that have
either been encrypted or signed, but not both.
This adds a couple tests of signed+encrypted messages, one where the
subject line is masked (outside subject line is "Subject Unavailable")
and another where it is not (outside Subject: matches inner Subject:)
See the discussion at
https://dkg.fifthhorseman.net/blog/e-mail-cryptography.html#protected-headers
for more details about the nuances between signed, stripped, and
stubbed headers.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
When indexing the cleartext of an encrypted message, record any
protected subject in the database, which should make it findable and
visible in search.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Now that we can decrypt headers, we want to make sure that clients
using "notmuch reply" to prepare a reply don't leak cleartext in their
subject lines. In particular, the ["reply-headers"]["Subject"] should
by default show the external Subject.
A replying MUA that intends to protect the Subject line should show
the user the Subject from ["original"]["headers"]["Subject"] instead
of using ["reply-headers"]["Subject"].
This minor asymmetry with "notmuch show" is intentional. While both
tools always render the cleartext subject line when they know it (in
["headers"]["Subject"] for "notmuch show" and in
["original"]["headers"]["Subject"] for "notmuch reply"), "notmuch
reply" should never leak something that should stay under encrypted
cover in "reply-headers".
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Make sure that we emit the correct cryptographic envelope status for
cleartext signed messages.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Adding another test to ensure that we handle protected headers
gracefully when no external subject is present.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
The header-mask member of the per-message crypto object allows a
clever UI frontend to mark whether a header was protected (or not).
And if it was protected, it contains enough information to show useful
detail to an interested user. For example, an MUA could offer a "show
what this message's Subject looked like on the wire" feature in expert
mode.
As before, we only handle Subject for now, but we might be able to
handle other headers in the future.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Amended by db: tweaked schemata notation.
Correctly fix the two outstanding tests so that the protected (hidden)
subject is properly reported.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Here we add several variant e-mail messages, some of which have
correctly-structured protected headers, and some of which do not. The
goal of the tests is to ensure that the right protected subjects get
reported.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
