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Convert HashBytes to VarChar

Tags:

sql

sql-server

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What is SQL Server Hashbytes?

Specifies an expression that evaluates to a character or binary string to be hashed. The output conforms to the algorithm standard: 128 bits (16 bytes) for MD2, MD4, and MD5; 160 bits (20 bytes) for SHA and SHA1; 256 bits (32 bytes) for SHA2_256, and 512 bits (64 bytes) for SHA2_512.

Is Hashbytes reversible?

The SQL hashbytes function can use a number of different algorithms, but none of the are reversible. They are all hashing algorithms, not encryption algorithms.


I have found the solution else where:

SELECT SUBSTRING(master.dbo.fn_varbintohexstr(HashBytes('MD5', 'HelloWorld')), 3, 32)

SELECT CONVERT(NVARCHAR(32),HashBytes('MD5', 'Hello World'),2)

Use master.dbo.fn_varbintohexsubstring(0, HashBytes('SHA1', @input), 1, 0) instead of master.dbo.fn_varbintohexstr and then substringing the result.

In fact fn_varbintohexstr calls fn_varbintohexsubstring internally. The first argument of fn_varbintohexsubstring tells it to add 0xF as the prefix or not. fn_varbintohexstr calls fn_varbintohexsubstring with 1 as the first argument internaly.

Because you don't need 0xF, call fn_varbintohexsubstring directly.


Contrary to what David Knight says, these two alternatives return the same response in MS SQL 2008:

SELECT CONVERT(VARCHAR(32),HashBytes('MD5', 'Hello World'),2)
SELECT UPPER(master.dbo.fn_varbintohexsubstring(0, HashBytes('MD5', 'Hello World'), 1, 0))

So it looks like the first one is a better choice, starting from version 2008.


convert(varchar(34), HASHBYTES('MD5','Hello World'),1)

(1 for converting hexadecimal to string)

convert this to lower and remove 0x from the start of the string by substring:

substring(lower(convert(varchar(34), HASHBYTES('MD5','Hello World'),1)),3,32)

exactly the same as what we get in C# after converting bytes to string


With personal experience of using the following code within a Stored Procedure which Hashed a SP Variable I can confirm, although undocumented, this combination works 100% as per my example:

@var=SUBSTRING(master.dbo.fn_varbintohexstr(HashBytes('SHA2_512', @SPvar)), 3, 128)