Add signature verification of PGP/MIME-signed parts with --verify.

This is primarily for notmuch-show, although the functionality is
added to show-message.  Once signatures are processed a new
part_sigstatus formatter is emitted, and the entire multipart/signed
part is replaced with the contents of the signed part.

At the moment only a json part_sigstatus formatting function is
available.  Emacs support to follow.

The original work for this patch was done by

  Daniel Kahn Gillmor <dkg@fifthhorseman.net>

whose help with this functionality I greatly appreciate.

Makefile.local

@@ -246,6 +246,7 @@ notmuch_client_srcs =		\
 	notmuch-show.c		\
 	notmuch-tag.c		\
 	notmuch-time.c		\
+	notmuch-gmime-session.c \
 	query-string.c		\
 	show-message.c		\
 	json.c			\

notmuch-client.h

@@ -67,6 +67,7 @@ typedef struct notmuch_show_format {
     const char *body_start;
     void (*part_start) (GMimeObject *part,
 			int *part_count);
+    void (*part_sigstatus) (const GMimeSignatureValidity* validity);
     void (*part_content) (GMimeObject *part);
     void (*part_end) (GMimeObject *part);
     const char *part_sep;
@@ -80,6 +81,7 @@ typedef struct notmuch_show_params {
     int entire_thread;
     int raw;
     int part;
+    GMimeCipherContext* cryptoctx;
 } notmuch_show_params_t;
 
 /* There's no point in continuing when we've detected that we've done
@@ -233,4 +235,7 @@ notmuch_config_set_maildir_synchronize_flags (notmuch_config_t *config,
 notmuch_bool_t
 debugger_is_active (void);
 
+GType
+notmuch_gmime_session_get_type (void);
+
 #endif

notmuch-gmime-session.c

@@ -0,0 +1,49 @@
+#include "notmuch-client.h"
+
+/* CRUFTY BOILERPLATE for GMimeSession (dkg thinks this will go away once GMime 2.6 comes out) */
+typedef struct _NotmuchGmimeSession NotmuchGmimeSession;
+typedef struct _NotmuchGmimeSessionClass NotmuchGmimeSessionClass;
+
+struct _NotmuchGmimeSession {
+    GMimeSession parent_object;
+};
+
+struct _NotmuchGmimeSessionClass {
+    GMimeSessionClass parent_class;
+};
+
+static void notmuch_gmime_session_class_init (NotmuchGmimeSessionClass *klass);
+
+static GMimeSessionClass *parent_class = NULL;
+
+GType
+notmuch_gmime_session_get_type (void)
+{
+    static GType type = 0;
+
+    if (!type) {
+	static const GTypeInfo info = {
+	    sizeof (NotmuchGmimeSessionClass),
+	    NULL, /* base_class_init */
+	    NULL, /* base_class_finalize */
+	    (GClassInitFunc) notmuch_gmime_session_class_init,
+	    NULL, /* class_finalize */
+	    NULL, /* class_data */
+	    sizeof (NotmuchGmimeSession),
+	    0,    /* n_preallocs */
+	    NULL, /* object_init */
+	    NULL, /* value_table */
+	};
+	type = g_type_register_static (GMIME_TYPE_SESSION, "NotmuchGmimeSession", &info, 0);
+    }
+    return type;
+}
+
+static void
+notmuch_gmime_session_class_init (NotmuchGmimeSessionClass *klass)
+{
+    GMimeSessionClass *session_class = GMIME_SESSION_CLASS (klass);
+    parent_class = g_type_class_ref (GMIME_TYPE_SESSION);
+    session_class->request_passwd = NULL;
+}
+/* END CRUFTY BOILERPLATE */

notmuch-reply.c

@@ -32,6 +32,7 @@ static const notmuch_show_format_t format_reply = {
 	"", NULL,
 	    "", NULL, "",
 	    "",
+	        NULL,
 	        NULL,
 	        reply_part_content,
 	        NULL,
@@ -447,6 +448,7 @@ notmuch_reply_format_default(void *ctx, notmuch_config_t *config, notmuch_query_
     const notmuch_show_format_t *format = &format_reply;
     notmuch_show_params_t params;
     params.part = -1;
+    params.cryptoctx = NULL;
 
     for (messages = notmuch_query_search_messages (query);
 	 notmuch_messages_valid (messages);

notmuch-show.c

@@ -44,6 +44,7 @@ static const notmuch_show_format_t format_text = {
 	    "\fheader{\n", format_headers_text, "\fheader}\n",
 	    "\fbody{\n",
 	        format_part_start_text,
+	        NULL,
 	        format_part_content_text,
 	        format_part_end_text,
 	        "",
@@ -64,6 +65,9 @@ static void
 format_part_start_json (unused (GMimeObject *part),
 			int *part_count);
 
+static void
+format_part_sigstatus_json (const GMimeSignatureValidity* validity);
+
 static void
 format_part_content_json (GMimeObject *part);
 
@@ -76,6 +80,7 @@ static const notmuch_show_format_t format_json = {
 	    ", \"headers\": {", format_headers_json, "}",
 	    ", \"body\": [",
 	        format_part_start_json,
+	        format_part_sigstatus_json,
 	        format_part_content_json,
 	        format_part_end_json,
 	        ", ",
@@ -97,6 +102,7 @@ static const notmuch_show_format_t format_mbox = {
                 NULL,
                 NULL,
                 NULL,
+                NULL,
                 "",
             "",
         "", "",
@@ -111,6 +117,7 @@ static const notmuch_show_format_t format_raw = {
 	"", NULL,
 	    "", NULL, "",
             "",
+                NULL,
                 NULL,
                 format_part_content_raw,
                 NULL,
@@ -396,6 +403,22 @@ show_part_content (GMimeObject *part, GMimeStream *stream_out)
 	g_object_unref(stream_filter);
 }
 
+static const char*
+signerstatustostring (GMimeSignerStatus x)
+{
+    switch (x) {
+    case GMIME_SIGNER_STATUS_NONE:
+	return "none";
+    case GMIME_SIGNER_STATUS_GOOD:
+	return "good";
+    case GMIME_SIGNER_STATUS_BAD:
+	return "bad";
+    case GMIME_SIGNER_STATUS_ERROR:
+	return "error";
+    }
+    return "unknown";
+}
+
 static void
 format_part_start_text (GMimeObject *part, int *part_count)
 {
@@ -472,6 +495,65 @@ format_part_start_json (unused (GMimeObject *part), int *part_count)
     printf ("{\"id\": %d", *part_count);
 }
 
+static void
+format_part_sigstatus_json (const GMimeSignatureValidity* validity)
+{
+    printf (", \"sigstatus\": [");
+
+    if (!validity) {
+	printf ("]");
+	return;
+    }
+
+    const GMimeSigner *signer = g_mime_signature_validity_get_signers (validity);
+    int first = 1;
+    void *ctx_quote = talloc_new (NULL);
+
+    while (signer) {
+	if (first)
+	    first = 0;
+	else
+	    printf (", ");
+
+	printf ("{");
+
+	/* status */
+	printf ("\"status\": %s", json_quote_str (ctx_quote, signerstatustostring(signer->status)));
+
+	if (signer->status == GMIME_SIGNER_STATUS_GOOD)
+	{
+	    if (signer->fingerprint)
+		printf (", \"fingerprint\": %s", json_quote_str (ctx_quote, signer->fingerprint));
+	    /* these dates are seconds since the epoch; should we
+	     * provide a more human-readable format string? */
+	    if (signer->created)
+		printf (", \"created\": %d", (int) signer->created);
+	    if (signer->expires)
+		printf (", \"expires\": %d", (int) signer->expires);
+	    /* output user id only if validity is FULL or ULTIMATE. */
+	    /* note that gmime is using the term "trust" here, which
+	     * is WRONG.  It's actually user id "validity". */
+	    if ((signer->name) && (signer->trust)) {
+		if ((signer->trust == GMIME_SIGNER_TRUST_FULLY) || (signer->trust == GMIME_SIGNER_TRUST_ULTIMATE))
+		    printf (", \"userid\": %s", json_quote_str (ctx_quote, signer->name));
+           }
+       } else {
+           if (signer->keyid)
+               printf (", \"keyid\": %s", json_quote_str (ctx_quote, signer->keyid));
+       }
+       if (signer->errors != GMIME_SIGNER_ERROR_NONE) {
+           printf (", \"errors\": %x", signer->errors);
+       }
+
+       printf ("}");
+       signer = signer->next;
+    }
+
+    printf ("]");
+
+    talloc_free (ctx_quote);
+}
+
 static void
 format_part_content_json (GMimeObject *part)
 {
@@ -739,6 +821,7 @@ notmuch_show_command (void *ctx, unused (int argc), unused (char *argv[]))
     params.entire_thread = 0;
     params.raw = 0;
     params.part = -1;
+    params.cryptoctx = NULL;
 
     for (i = 0; i < argc && argv[i][0] == '-'; i++) {
 	if (strcmp (argv[i], "--") == 0) {
@@ -767,6 +850,16 @@ notmuch_show_command (void *ctx, unused (int argc), unused (char *argv[]))
 	    params.part = atoi(argv[i] + sizeof ("--part=") - 1);
 	} else if (STRNCMP_LITERAL (argv[i], "--entire-thread") == 0) {
 	    params.entire_thread = 1;
+	} else if (STRNCMP_LITERAL (argv[i], "--verify") == 0) {
+	    if (params.cryptoctx == NULL) {
+		GMimeSession* session = g_object_new(notmuch_gmime_session_get_type(), NULL);
+		if (NULL == (params.cryptoctx = g_mime_gpg_context_new(session, "gpg")))
+		    fprintf (stderr, "Failed to construct gpg context.\n");
+		else
+		    g_mime_gpg_context_set_always_trust((GMimeGpgContext*)params.cryptoctx, FALSE);
+		g_object_unref (session);
+		session = NULL;
+	    }
 	} else {
 	    fprintf (stderr, "Unrecognized option: %s\n", argv[i]);
 	    return 1;
@@ -824,5 +917,8 @@ notmuch_show_command (void *ctx, unused (int argc), unused (char *argv[]))
     notmuch_query_destroy (query);
     notmuch_database_close (notmuch);
 
+    if (params.cryptoctx)
+	g_object_unref(params.cryptoctx);
+
     return 0;
 }

notmuch.1

@@ -321,6 +321,17 @@ a depth-first walk of the message MIME structure, and are identified
 in the 'json' or 'text' output formats.
 .RE
 
+.RS 4
+.TP 4
+.B \-\-verify
+
+Compute and report the validity of any MIME cryptographic signatures
+found in the selected content (ie. "multipart/signed" parts). Status
+of the signature will be reported (currently only supported with
+--format=json), and the multipart/signed part will be replaced by the
+signed data.
+.RE
+
 A common use of
 .B notmuch show
 is to display a single thread of email messages. For this, use a

notmuch.c

@@ -294,6 +294,14 @@ static command_t commands[] = {
       "\t\tmessage MIME structure, and are identified in the 'json' or\n"
       "\t\t'text' output formats.\n"
       "\n"
+      "\t--verify\n"
+      "\n"
+      "\t\tCompute and report the validity of any MIME cryptographic\n"
+      "\t\tsignatures found in the selected content (ie.\n"
+      "\t\t\"multipart/signed\" parts). Status of the signature will be\n"
+      "\t\treported (currently only supported with --format=json) and\n"
+      "\t\tthe multipart/signed part will be replaced by the signed data.\n"
+      "\n"
       "\n"
       "\tA common use of \"notmuch show\" is to display a single\n"
       "\tthread of email messages. For this, use a search term of\n"

show-message.c

@@ -51,9 +51,48 @@ show_message_part (GMimeObject *part,
 
 	if (format->part_start)
 	    format->part_start (part, &(state->part_count));
-	format->part_content (part);
     }
 
+    /* handle PGP/MIME parts */
+    if (GMIME_IS_MULTIPART (part) && params->cryptoctx) {
+	GMimeMultipart *multipart = GMIME_MULTIPART (part);
+	GError* err = NULL;
+
+	if (GMIME_IS_MULTIPART_SIGNED (part))
+	{
+	    if ( g_mime_multipart_get_count (multipart) != 2 ) {
+		/* this violates RFC 3156 section 5, so we won't bother with it. */
+		fprintf (stderr,
+			 "Error: %d part(s) for a multipart/signed message (should be exactly 2)\n",
+			 g_mime_multipart_get_count (multipart));
+	    } else {
+		/* For some reason the GMimeSignatureValidity returned
+		 * here is not a const (inconsistent with that
+		 * returned by
+		 * g_mime_multipart_encrypted_get_signature_validity,
+		 * and therefore needs to be properly disposed of.
+		 * Hopefully the API will become more consistent. */
+		GMimeSignatureValidity *sigvalidity = g_mime_multipart_signed_verify (GMIME_MULTIPART_SIGNED (part), params->cryptoctx, &err);
+		if (!sigvalidity) {
+		    fprintf (stderr, "Failed to verify signed part: %s\n", (err ? err->message : "no error explanation given"));
+		}
+		if ((selected || state->in_zone) && format->part_sigstatus)
+		    format->part_sigstatus (sigvalidity);
+		/* extract only data part, and ignore signature part */
+		part = g_mime_multipart_get_part (multipart, 0);
+		if (sigvalidity)
+		    g_mime_signature_validity_free (sigvalidity);
+	    }
+	}
+
+	if (err)
+	    g_error_free (err);
+    }
+    /* end handle PGP/MIME parts */
+
+    if (selected || state->in_zone)
+	format->part_content (part);
+
     if (GMIME_IS_MULTIPART (part)) {
 	GMimeMultipart *multipart = GMIME_MULTIPART (part);
 	int i;