diff -r 11789a88d0b0 -r 76bd29a11cc9 dav/main.c
--- a/dav/main.c	Sun Dec 17 14:35:01 2017 +0100
+++ b/dav/main.c	Tue Dec 12 23:36:47 2017 +0100
@@ -942,8 +942,17 @@
             return -1;
         }
     }
+
+    // if encryption is requested, but we still don't know the key, abort
+    if (DAV_IS_ENCRYPTED(sn) && !(sn->key)) {
+        fprintf(stderr, "Encryption has been requested, "
+                "but no default key is configured.\n"
+                "You may specify a custom key with the '-k' option.\n");
+        return -1;
+    }
     
     char *tar = cmd_getoption(a, "tar");
+    
     int ret;
     if(!tar) {
         if(!strcmp(file, "-")) {