chunk: Add predictable hash function

Since chunk_hash() is randomized its output is not predictable, that is,
it is only within the same process.

src/libstrongswan/utils/chunk.c

@@ -705,6 +705,12 @@ u_int64_t chunk_mac(chunk_t chunk, u_char *key)
  */
 static u_char key[16];
 
+/**
+ * Static key used in case predictable hash values are required.
+ */
+static u_char static_key[] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+							  0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};
+
 /**
  * Only allocate the key once
  */
@@ -764,6 +770,22 @@ u_int32_t chunk_hash(chunk_t chunk)
 	return chunk_mac(chunk, key);
 }
 
+/**
+ * Described in header.
+ */
+u_int32_t chunk_hash_static_inc(chunk_t chunk, u_int32_t hash)
+{	/* we could use a mac of the previous hash, but this is faster */
+	return chunk_mac_inc(chunk, static_key, ((u_int64_t)hash) << 32 | hash);
+}
+
+/**
+ * Described in header.
+ */
+u_int32_t chunk_hash_static(chunk_t chunk)
+{
+	return chunk_mac(chunk, static_key);
+}
+
 /**
  * Described in header.
  */