diff --git a/rmcp.hpp b/rmcp.hpp
new file mode 100644
index 0000000..fd536cb
--- /dev/null
+++ b/rmcp.hpp
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <array>
+#include <cstdint>
+
+namespace rmcp
+{
+
+/*
+ * RSP needs more keying material than can be provided by session
+ * integrity key alone. As a result all keying material for the RSP
+ * confidentiality algorithms will be generated by processing a
+ * pre-defined set of constants using HMAC per [RFC2104], keyed by SIK.
+ * These constants are constructed using a hexadecimal octet value
+ * repeated up to the HMAC block size in length starting with the
+ * constant 01h. This mechanism can be used to derive up to 255
+ * HMAC-block-length pieces of keying material from a single SIK.For the
+ * mandatory confidentiality algorithm AES-CBC-128, processing the
+ * following constant will generate the required amount of keying
+ * material.
+ */
+constexpr size_t CONST_N_SIZE = 20;
+using Const_n = std::array<uint8_t, CONST_N_SIZE>;
+
+static constexpr Const_n const_1 = {
+    0x01, 0x01, 0x01, 0x01, 0x01,
+    0x01, 0x01, 0x01, 0x01, 0x01,
+    0x01, 0x01, 0x01, 0x01, 0x01,
+    0x01, 0x01, 0x01, 0x01, 0x01
+};
+
+static constexpr Const_n const_2 = {
+    0x02, 0x02, 0x02, 0x02, 0x02,
+    0x02, 0x02, 0x02, 0x02, 0x02,
+    0x02, 0x02, 0x02, 0x02, 0x02,
+    0x02, 0x02, 0x02, 0x02, 0x02
+};
+
+} // namespace rmcp