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Wednesday, 30 March 2011

How to protect code written in Stored Procedure or User Defined Function?

We have always been wondering on how to protect/secure our t-sql code written in Stored Procedures and UDF in shared hosting environment from other people who might tweak our work. Here, I would discuss a few options I know to serve purpose.
As per my knowledge, MS SQL Server doesn’t help much with it. The possible alternatives which could be tried are –
  1.        Making Use of WITH ENCRYPTION option

The normal way of creating a stored procedure is -

CREATE PROCEDURE dbo.SimpleStoredProc
    SELECT 'Some t-sql statements'

Creating the stored procedure using the WITH EXCRYPTION option is -

CREATE PROCEDURE dbo.EncryptedStoredProc
    SELECT 'Some t-sql statements'

However, please make sure that the code of the SP is backed up as a separate script file for future references.

Now, when we try to use the following command to get the details of the SP -
EXEC sp_helptext 'dbo.EncryptedStoredProc'

We get the following error message –
The object comments have been encrypted.

And when we try to open this encrypted SP using SSMS, we get the following error message –

Microsoft SQL-DMO
Error 20585: [SQL-DMO]
    Encrypted object is not transferable,
    and script can not be generated.

a.       Once encrypted, it is not possible to decrypt using SQL Server commands.

a.       We as developers will always have to keep a copy of the SP/UDF as a script for our reference or future updates.
b.      One way I know using which this approach could be defeated is by running SQL Profiler while executing the stored procedure.
c.       Another way that users might use to get at your encrypted code is by using readily available code (if any) that allows you to break SQL Server's relatively trivial encryption algorithm. 
2.       Stop creating Stored Procedures and Functions

The very first question which comes to our mind is – if we stop creating them, then what is the alternative. We might use an of the below stated technique –
a.       Make use of Parameterized queries directly in our source code. As the code is deployed in the form of an assembly, it becomes hard to directly get into our query logic. However, de-compilation is always possible and to tackle it we can always obfuscate our assemblies. To learn more about obfuscation please refer http://msdn.microsoft.com/en-us/magazine/cc164058.aspx
b.      Secondly, we can make use of sql-clr functions wherever possible. This would again help us in hiding our logic from the preying eyes. Please refer http://msdn.microsoft.com/en-us/library/ms345136(v=sql.90).aspx for more details.

One should not make use of WITH ENCRYPTION option unless it’s the last option and have a thorough knowledge of its consequences after implementation. However, I would strongly recommend NOT TO USE it.

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