diff --git a/lualib/md5.lua b/lualib/md5.lua
index 26f5cfa6..ceaddb38 100644
--- a/lualib/md5.lua
+++ b/lualib/md5.lua
@@ -15,4 +15,22 @@ function core.sumhexa (k)
 		 end))
 end
 
-return core
\ No newline at end of file
+function core.hmac_md5(data,key)
+	if #key>64 then
+		key=core.sum(key)
+		key=string.sub(key,1,16)
+	end
+
+	local b=table.pack(string.byte(key,1,#key))
+	local ipad_s=""
+	local opad_s=""
+	for i=1,64 do
+		ipad_s=ipad_s..string.char((b[i] or 0)~0x36)
+		opad_s=opad_s..string.char((b[i] or 0)~0x5c)
+	end
+	local istr=core.sum(ipad_s..data)
+	local ostr=core.sumhexa(opad_s..istr)
+	return ostr
+end
+
+return core