diff --git a/checksum.h b/checksum.h
new file mode 100644
index 0000000..fb987e1
--- /dev/null
+++ b/checksum.h
@@ -0,0 +1,5 @@
+uint32_t sum_16b(void *buf, size_t len);
+uint16_t csum_fold(uint32_t sum);
+uint16_t csum_unaligned(void *buf, size_t len, uint32_t init);
+void csum_tcp4(struct iphdr *iph);
+uint16_t csum(const void *buf, size_t len, uint32_t init);