--- a/fuzzer-preauth.c	Thu May 25 22:21:23 2017 +0800
+++ b/fuzzer-preauth.c	Thu May 25 22:21:49 2017 +0800
@@ -19,6 +19,23 @@
 		return 0;
 	}
 
+    // get prefix. input format is
+    // string prefix
+    //     uint32 wrapfd seed
+    //     ... to be extended later
+    // [bytes] ssh input stream
+
+    // be careful to avoid triggering buffer.c assertions
+    if (fuzz.input->len < 8) {
+        return 0;
+    }
+    size_t prefix_size = buf_getint(fuzz.input);
+    if (prefix_size != 4) {
+        return 0;
+    }
+    uint32_t wrapseed = buf_getint(fuzz.input);
+    wrapfd_setseed(wrapseed);
+
 	int fakesock = 1;
 	wrapfd_add(fakesock, fuzz.input, PLAIN);