chunk: Add function to calculate Internet Checksums according to RFC 1071

src/libstrongswan/utils/chunk.c

@@ -987,6 +987,37 @@ u_int32_t chunk_hash_static(chunk_t chunk)
 	return chunk_mac(chunk, static_key);
 }
 
+/**
+ * Described in header.
+ */
+u_int16_t chunk_internet_checksum_inc(chunk_t data, u_int16_t checksum)
+{
+	u_int32_t sum = ntohs(~checksum);
+
+	while (data.len > 1)
+	{
+		sum += untoh16(data.ptr);
+		data = chunk_skip(data, 2);
+	}
+	if (data.len)
+	{
+		sum += (u_int16_t)*data.ptr << 8;
+	}
+	while (sum >> 16)
+	{
+		sum = (sum & 0xffff) + (sum >> 16);
+	}
+	return htons(~sum);
+}
+
+/**
+ * Described in header.
+ */
+u_int16_t chunk_internet_checksum(chunk_t data)
+{
+	return chunk_internet_checksum_inc(data, 0xffff);
+}
+
 /**
  * Described in header.
  */

src/libstrongswan/utils/chunk.h

@@ -411,6 +411,31 @@ u_int32_t chunk_hash_static_inc(chunk_t chunk, u_int32_t hash);
  */
 u_int64_t chunk_mac(chunk_t chunk, u_char *key);
 
+/**
+ * Calculate the Internet Checksum according to RFC 1071 for the given chunk.
+ *
+ * If the result is used with chunk_internet_checksum_inc() and the data length
+ * is not a multiple of 16 bit the checksum bytes have to be swapped to
+ * compensate the even/odd alignment.
+ *
+ * @param chunk			data to process
+ * @return				checksum (one's complement, network order)
+ */
+u_int16_t chunk_internet_checksum(chunk_t data);
+
+/**
+ * Extend the given Internet Checksum (one's complement, in network byte order)
+ * with the given data.
+ *
+ * If data is not a multiple of 16 bits the checksum may have to be swapped to
+ * compensate even/odd alignment (see chunk_internet_checksum()).
+ *
+ * @param chunk			data to process
+ * @param checksum		previous checksum (one's complement, network order)
+ * @return				checksum (one's complement, network order)
+ */
+u_int16_t chunk_internet_checksum_inc(chunk_t data, u_int16_t checksum);
+
 /**
  * printf hook function for chunk_t.
  *