diff --git a/lualib/md5.lua b/lualib/md5.lua
index 26f5cfa6..90e28739 100644
--- a/lualib/md5.lua
+++ b/lualib/md5.lua
@@ -15,4 +15,24 @@ function core.sumhexa (k)
 		 end))
 end
 
-return core
\ No newline at end of file
+local function get_ipad(c)
+	return string.char(c:byte() ~ 0x36)
+end
+
+local function get_opad(c)
+	return string.char(c:byte() ~ 0x5c)
+end
+
+function core.hmacmd5(data,key)
+	if #key>64 then
+		key=core.sum(key)
+		key=key:sub(1,16)
+	end
+	local ipad_s=key:gsub(".", get_ipad)..string.rep("6",64-#key)
+	local opad_s=key:gsub(".", get_opad)..string.rep("\\",64-#key)
+	local istr=core.sum(ipad_s..data)
+	local ostr=core.sumhexa(opad_s..istr)
+	return ostr
+end
+
+return core