How to Encoding and Decoding Base64 strings in C# and SQL server

In C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
public class encode_decode
{
    public static string EncodeTo64(string toEncode)
    {
        byte[] toEncodeAsBytes = System.Text.Encoding.UTF8.GetBytes(toEncode);
        string returnValue = System.Convert.ToBase64String(toEncodeAsBytes);
        return returnValue;
    }
    public static string DecodeFrom64(string encodedData)
    {
        byte[] encodedDataAsBytes = System.Convert.FromBase64String(encodedData);
        string returnValue = System.Text.Encoding.UTF8.GetString(encodedDataAsBytes);
        return returnValue;
    }
}
In SQL server
CREATE  FUNCTION [dbo].[fn_base64_encode_decode]
(
@in_mode INT ,
@in_input VARCHAR(MAX)
)
RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE @encoded_decode_base64 VARCHAR(MAX),@source VARBINARY(MAX)
IF @in_mode = 1 --ENCODE
BEGIN
SET @source = CONVERT(VARBINARY(MAX), @in_input)
SELECT @encoded_decode_base64 = CAST(N'' AS
                xml).value('xs:base64Binary(sql:variable("@source"))', 'VARCHAR(MAX)')
END
IF @in_mode = 2 --DECODE
BEGIN
SELECT @encoded_decode_base64 = CAST(N'' AS
                xml).value('xs:base64Binary(sql:variable("@in_input"))', 'VARBINARY(MAX)')
END
RETURN @encoded_decode_base64
END