[PATCH v2 09/17] cli/reply: ensure encrypted Subject: line does not leak in the clear

[Daniel Kahn Gillmor]

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 at fifthhorseman.net>
---
 test/T356-protected-headers.sh | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/test/T356-protected-headers.sh b/test/T356-protected-headers.sh
index 62d7e210..ff37f6bd 100755
--- a/test/T356-protected-headers.sh
+++ b/test/T356-protected-headers.sh
@@ -76,4 +76,11 @@ output=$(notmuch show --verify --format=json id:signed-protected-header at crypto.n
 test_json_nodes <<<"$output" \
                 'crypto:[0][0][0]["crypto"]={"signed": {"status": [{"created": 1525350527, "fingerprint": "'$FINGERPRINT'", "userid": "'"$SELF_USERID"'", "status": "good"}], "headers": ["Subject"]}}'
 
+test_begin_subtest "protected subject does not leak by default in replies"
+output=$(notmuch reply --decrypt=true --format=json id:protected-header at crypto.notmuchmail.org)
+test_json_nodes <<<"$output" \
+                'crypto:["original"]["crypto"]={"decrypted": {"status": "full", "header-mask": {"Subject": "Subject Unavailable"}}}' \
+                'subject:["original"]["headers"]["Subject"]="This is a protected header"' \
+                'reply-subject:["reply-headers"]["Subject"]="Re: Subject Unavailable"'
+
 test_done
-- 
2.20.1