diff -uprN bird-as4-md5old/nest/a-path.c bird-as4-md5/nest/a-path.c
--- bird-as4-md5old/nest/a-path.c	2008-10-13 23:41:05.000000000 +0200
+++ bird-as4-md5/nest/a-path.c	2008-10-07 19:00:12.000000000 +0200
@@ -100,7 +100,6 @@ as_path_convert_to_old(struct adata *pat
   return dst - dst_start;
 }
 
-
 int
 as_path_convert_to_new(struct adata *path, byte *dst, int req_as)
 {
@@ -141,8 +140,6 @@ as_path_convert_to_new(struct adata *pat
   return dst - dst_start;
 }
 
-
-
 void
 as_path_format(struct adata *path, byte *buf, unsigned int size)
 {
diff -uprN bird-as4-md5old/nest/attrs.h bird-as4-md5/nest/attrs.h
--- bird-as4-md5old/nest/attrs.h	2008-10-13 23:41:05.000000000 +0200
+++ bird-as4-md5/nest/attrs.h	2008-10-07 19:04:14.000000000 +0200
@@ -17,6 +17,9 @@
 #define AS_PATH_MAXLEN		10000
 
 #define AS_TRANS		23456
+/* AS_TRANS is used when we need to store 32bit ASN larger than 0xFFFF
+ * to 16bit slot (like in 16bit AS_PATH). See RFC 4893 for details
+ */
 
 struct adata *as_path_prepend(struct linpool *pool, struct adata *olda, u32 as);
 int as_path_convert_to_old(struct adata *path, byte *dst, int *new_used);
diff -uprN bird-as4-md5old/sysdep/unix/io.c bird-as4-md5/sysdep/unix/io.c
--- bird-as4-md5old/sysdep/unix/io.c	2008-10-13 23:41:50.000000000 +0200
+++ bird-as4-md5/sysdep/unix/io.c	2008-10-13 23:43:09.000000000 +0200
@@ -644,14 +644,7 @@ bad:
 }
 
 
-/* Add / remove MD5 signature association for given socket.
- * There is a set of pairs (address, password) used to choose
- * password according to address of the other side.
- * When called with passwd != NULL, the new pair is added,
- * When called with passwd == NULL, the existing pair is removed.
- *
- * FIXME: check portability
- */
+/* FIXME: check portability  */
 
 static int
 sk_set_md5_auth_int(sock *s, sockaddr *sa, char *passwd)
@@ -688,6 +681,24 @@ sk_set_md5_auth_int(sock *s, sockaddr *s
   return rv;
 }
 
+/**
+ * sk_set_md5_auth - add / remove MD5 security association for given socket.
+ * @s: socket
+ * @a: IP address of the other side
+ * @passwd: password used for MD5 authentication
+ *
+ * In TCP MD5 handling code in kernel, there is a set of pairs
+ * (address, password) used to choose password according to
+ * address of the other side. This function is useful for
+ * listening socket, for active sockets it is enough to set
+ * s->password field.
+ *
+ * When called with passwd != NULL, the new pair is added,
+ * When called with passwd == NULL, the existing pair is removed.
+ *
+ * Result: 0 for success, -1 for an error.
+ */
+
 int
 sk_set_md5_auth(sock *s, ip_addr a, char *passwd)
 {
@@ -861,7 +872,7 @@ sk_open(sock *s)
     }
   fill_in_sockaddr(&sa, s->daddr, s->dport);
 
-  if (s->password != NULL)
+  if (s->password)
     {
       int rv = sk_set_md5_auth_int(s, &sa, s->password);
       if (rv < 0)