From a6b0772b60d9191fcc291358eec3d78bfea31f1c Mon Sep 17 00:00:00 2001 From: Daniel Kahn Gillmor Date: Sun, 26 May 2019 18:15:55 -0400 Subject: [PATCH] util/crypto: add information about the payload part When walking the MIME tree, if we discover that we are at the cryptographic payload, then we would like to record at least the Subject header of the current MIME part. In the future, we might want to record many other headers as well, but for now we will stick with just the Subject. See https://dkg.fifthhorseman.net/blog/e-mail-cryptography.html#cryptographic-envelope for more description of the Cryptographic Payload vs. the Cryptographic Envelope. Signed-off-by: Daniel Kahn Gillmor --- util/crypto.c | 37 +++++++++++++++++++++++++++++++++++++ util/crypto.h | 5 +++++ 2 files changed, 42 insertions(+) diff --git a/util/crypto.c b/util/crypto.c index 3f8ac25a..9e185e03 100644 --- a/util/crypto.c +++ b/util/crypto.c @@ -90,6 +90,8 @@ _notmuch_message_crypto_destructor (_notmuch_message_crypto_t *msg_crypto) return 0; if (msg_crypto->sig_list) g_object_unref (msg_crypto->sig_list); + if (msg_crypto->payload_subject) + talloc_free (msg_crypto->payload_subject); return 0; } @@ -133,6 +135,10 @@ _notmuch_message_crypto_potential_sig_list (_notmuch_message_crypto_t *msg_crypt notmuch_status_t _notmuch_message_crypto_potential_payload (_notmuch_message_crypto_t *msg_crypto, GMimeObject *payload, GMimeObject *parent, int childnum) { + const char *protected_headers = NULL; + const char *forwarded = NULL; + const char *subject = NULL; + if (!msg_crypto || !payload) return NOTMUCH_STATUS_NULL_POINTER; @@ -156,6 +162,37 @@ _notmuch_message_crypto_potential_payload (_notmuch_message_crypto_t *msg_crypto msg_crypto->payload_encountered = true; + /* don't bother recording anything if there is no cryptographic + * envelope: */ + if ((msg_crypto->decryption_status != NOTMUCH_MESSAGE_DECRYPTED_FULL) && + (msg_crypto->sig_list == NULL)) + return NOTMUCH_STATUS_SUCCESS; + + /* Verify that this payload has headers that are intended to be + * exported to the larger message: */ + + /* Consider a payload that uses Alexei Melinkov's forwarded="no" for + * message/global or message/rfc822: + * https://tools.ietf.org/html/draft-melnikov-smime-header-signing-05#section-4 */ + forwarded = g_mime_object_get_content_type_parameter (payload, "forwarded"); + if (GMIME_IS_MESSAGE_PART (payload) && forwarded && strcmp (forwarded, "no") == 0) { + GMimeMessage *message = g_mime_message_part_get_message (GMIME_MESSAGE_PART (payload)); + subject = g_mime_message_get_subject (message); + /* FIXME: handle more than just Subject: at some point */ + } else { + /* Consider "memoryhole"-style protected headers as practiced by Enigmail and K-9 */ + protected_headers = g_mime_object_get_content_type_parameter (payload, "protected-headers"); + if (protected_headers && strcasecmp("v1", protected_headers) == 0) + subject = g_mime_object_get_header (payload, "Subject"); + /* FIXME: handle more than just Subject: at some point */ + } + + if (subject) { + if (msg_crypto->payload_subject) + talloc_free (msg_crypto->payload_subject); + msg_crypto->payload_subject = talloc_strdup (msg_crypto, subject); + } + return NOTMUCH_STATUS_SUCCESS; } diff --git a/util/crypto.h b/util/crypto.h index c6fa7f4b..fdbb5da5 100644 --- a/util/crypto.h +++ b/util/crypto.h @@ -59,6 +59,11 @@ typedef struct _notmuch_message_crypto { * is not part of the cryptographic envelope) */ bool payload_encountered; + /* the value of any "Subject:" header in the cryptographic payload + * (the top level part within the crypto envelope), converted to + * UTF-8 */ + char * payload_subject; + /* if both signed and encrypted, was the signature encrypted? */ bool signature_encrypted; } _notmuch_message_crypto_t;