HMAC function in Microsoft T-SQL

HMAC.sql

CREATE FUNCTION dbo.HMAC (
	@algo VARCHAR(20)
	,@key VARBINARY(MAX)
	,@data VARBINARY(MAX)
	)
	/* This function only takes VARBINARY parameters instead of VARCHAR
to prevent problems with implicit conversion from NVARCHAR to VARCHAR 
which result in incorrect hashes for inputs including non-ASCII characters. 
Always cast @key and @data parameters to VARBINARY when using this function. 
Tested against HMAC vectors for MD5 and SHA1 from RFC 2202 */

/*
List of secure hash algorithms (parameter @algo) supported by MSSQL 
version. This is what is passed to the HASHBYTES system function.
Omit insecure hash algorithms such as MD2 through MD5
2005-2008R2: SHA1 
2012-2016: SHA1 | SHA2_256 | SHA2_512 
*/
RETURNS VARBINARY(64)
AS
BEGIN
	DECLARE @ipad BIGINT
	DECLARE @opad BIGINT
	DECLARE @i VARBINARY(64)
	DECLARE @o VARBINARY(64)
	DECLARE @pos INTEGER

	--SQL 2005 only allows XOR operations on integer types, so use bigint and interate 8 times
	SET @ipad = cast(0x3636363636363636 AS BIGINT) --constants from HMAC definition
	SET @opad = cast(0x5C5C5C5C5C5C5C5C AS BIGINT)

	IF len(@key) > 64 --if the key is grater than 512 bits we hash it first per HMAC definition
		SET @key = cast(hashbytes(@algo, @key) AS BINARY (64))
	ELSE
		SET @key = cast(@key AS BINARY (64)) --otherwise pad it out to 512 bits with zeros

	SET @pos = 1
	SET @i = cast('' AS VARBINARY(64)) --initialize as empty binary value

	WHILE @pos <= 57
	BEGIN
		SET @i = @i + cast((substring(@key, @pos, 8) ^ @ipad) AS VARBINARY(64))
		SET @pos = @pos + 8
	END

	SET @pos = 1
	SET @o = cast('' AS VARBINARY(64)) --initialize as empty binary value

	WHILE @pos <= 57
	BEGIN
		SET @o = @o + cast((substring(@key, @pos, 8) ^ @opad) AS VARBINARY(64))
		SET @pos = @pos + 8
	END

	RETURN hashbytes(@algo, @o + hashbytes(@algo, @i + @data))
END
GO

GRANT EXECUTE
	ON dbo.HMAC
	TO PUBLIC
GO

/*
Copyright © 2012 Ryan Malayter. All Rights Reserved. 

Redistribution and use in source and binary forms, with or without 
modification, are permitted provided that the following conditions are 
met: 

1. Redistributions of source code must retain the above copyright 
notice, this list of conditions and the following disclaimer. 

2. Redistributions in binary form must reproduce the above copyright 
notice, this list of conditions and the following disclaimer in the 
documentation and/or other materials provided with the distribution. 

3. The name of the author may not be used to endorse or promote products 
derived from this software without specific prior written permission. 

THIS SOFTWARE IS PROVIDED BY Ryan Malayter "AS IS" AND ANY EXPRESS OR 
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
POSSIBILITY OF SUCH DAMAGE. 
*/

@NReilingh
Thanks for the prompt rely, I was using HMAC-SHA256 when encoding key.
I am calling my API server from SQL Server and server needs HMAC-SHA256 coded key. When i came across your script, i thought it is returning value in base64 but in fact it is returning in plain text.
`
DECLARE @b64 varbinary(max)
DECLARE @key varbinary(max) = CAST('d666f18176df4e29a64c7e40519a1751' AS varbinary(max))
DECLARE @message varbinary(max) = CAST('1e0950435dc94529cffdb67b1b679f3320082021' AS varbinary(max))

-- Return hash.
SELECT [dbo].HMAC('SHA2_256', @key, @message)
-- Returns 0a03375955fd7931ed26081a8ea941a1e26e1072c611425889d1e0293c6e527d

--Convert to base64
SELECT @b64 = [dbo].HMAC('SHA2_256', @key, @message)
SELECT cast(N'' as xml).value('xs:base64Binary(sql:variable("@b64"))', 'varchar(128)');

--Return: CgM3WVX9eTHtJggajqlBoeJuEHLGEUJYidHgKTxuUn0= "This is what i wanted"

`
Thanks again
MJ