SHA256 base 64 hash generation in SQL Server

Question

I need to generate a SHA256 base 64 hash from a table in SQL server but I can't find that algorithm in the list HASHBYTES arguments.

Is there a way to generate it directly in SQL Server?

Duplicate disclamer:

My question is not duplicate of SHA256 in T-sql stored procedure as I am looking for the SHA256 base 64 version of the algorithm which is not listed in the page.

Numeric Example

I have this query result in SQL Server

Start date,End date,POD,Amount,Currency

2016-01-01,2016-12-31,1234567890,12000,EUR

this give me the following string (using concatenate function)

2016-01-012016-12-31123456789012000EUR

whit this convertion tool I get the following hash

GMRzFNmm90KLVtO1kwTf7EcSeImq+96QTHgnWFFmZ0U

that I need to send to a customer.

Answer 1

First, the generator link you provided outputs the base64 representation in not exactly correct format. Namely, it omits the padding sequence. Though theoretically optional, padding is mandatory in MS SQL Server (tested on 2012 and 2016 versions).

With this in mind, the following code gives you what you need:

declare @s varchar(max), @hb varbinary(128), @h64 varchar(128);

select @s = '2016-01-012016-12-31123456789012000EUR';

set @hb = hashbytes('sha2_256', @s);
set @h64 = cast(N'' as xml).value('xs:base64Binary(sql:variable("@hb"))', 'varchar(128)');

select @hb as [BinaryHash], @h64 as [64Hash];

Apart from the aforementioned padding, there is another caveat for you to look for. Make sure that the input string is always of the same type, that is, either always varchar or always nvarchar. If some of your hashes will be calculated from ASCII strings and some from UTF-16, results will be completely different. Depending on which languages are used in your system, it might make sense to always convert the plain text to nvarchar before hashing.