e2e: Add matrix_sign_json

Given a JsonObject, produce a canonical json blob, sign it and
add the signature back into the JsonObject.

Signed-off-by: Dr. David Alan Gilbert <dave@treblig.org>

2 files changed, 48 insertions, 0 deletions

diff --git a/matrix-e2e.c b/matrix-e2e.c
index ec28820..71c1426 100644
--- a/matrix-e2e.c
+++ b/matrix-e2e.c
@@ -17,8 +17,10 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 #include "libmatrix.h"
 #include "matrix-e2e.h"
+#include "matrix-json.h"
 
 #include "connection.h"
 #ifndef MATRIX_NO_E2E
@@ -29,6 +31,50 @@ struct _MatrixE2EData {
     gchar *device_id;
 };
 
+/* Sign the JsonObject with olm_account_sign and add it to the object
+ * as a 'signatures' member of the top level object.
+ * 0 on success
+ */
+int matrix_sign_json(MatrixConnectionData *conn, JsonObject *tosign)
+{
+    int ret = -1;
+    OlmAccount *account = conn->e2e->oa;
+    const gchar *device_id = conn->e2e->device_id;
+    PurpleConnection *pc = conn->pc;
+    GString *can_json = matrix_canonical_json(tosign);
+    gchar *can_json_c = g_string_free(can_json, FALSE);
+    size_t sig_length = olm_account_signature_length(account);
+    gchar *sig = g_malloc0(sig_length+1);
+    if (olm_account_sign(account, can_json_c, strlen(can_json_c),
+            sig, sig_length)==olm_error()) {
+        purple_connection_error_reason(pc,
+                PURPLE_CONNECTION_ERROR_OTHER_ERROR,
+                olm_account_last_error(account));
+        goto out;
+    }
+
+    /* We need to add a "signatures" member which is an object, with
+     * a "user_id" member that is itself an object which has an "ed25519:$DEVICEID" member
+     * that is the signature.
+     */
+    GString *alg_dev = g_string_new(NULL);
+    g_string_printf(alg_dev, "ed25519:%s", device_id);
+    gchar *alg_dev_c = g_string_free(alg_dev, FALSE);
+    JsonObject *sig_dev = json_object_new();
+    json_object_set_string_member(sig_dev, alg_dev_c, sig);
+    JsonObject *sig_obj = json_object_new();
+    json_object_set_object_member(sig_obj, conn->user_id, sig_dev);
+    json_object_set_object_member(tosign, "signatures", sig_obj);
+    
+    g_free(alg_dev_c);
+    ret = 0;
+out:
+    g_free(can_json_c);
+    g_free(sig);
+
+    return ret;
+}
+
 #else
 /* ==== Stubs for when e2e is configured out of the build === */
 #endif
diff --git a/matrix-e2e.h b/matrix-e2e.h
index a2d8f9b..1ac190a 100644
--- a/matrix-e2e.h
+++ b/matrix-e2e.h
@@ -19,6 +19,8 @@
 #ifndef MATRIX_E2E_H
 #define MATRIX_E2E_H
 
+#include "matrix-connection.h"
+
 typedef struct _MatrixE2EData MatrixE2EData;
 
 #endif