articles

Articles of SQLschool.gr Team

The truth about WITH ENCRYPTION option

Antonios Chatzipavlis

Friday 07 October 2011

Όταν βάζουμε το WITH ENCRYPTION option σε μια stored procedure, ένα trigger, μια function ή ένα view ξέρουμε ότι αυτόματα ο κώδικας δεν είναι ορατός. Θα μπορούσαμε να πούμε ότι είναι κλειδωμένος.

Δεν ξέρω αν το γνωρίζεται αλλά ο SQL Server δεν είναι ένα digital rights management system αυτό σημαίνει ότι ο κώδικας που έχει γραφεί μέσα μια sp, function κλπ δεν είναι encrypted, αλλά απλά obfuscated.

Το obfuscation αυτό ο SQL Server εδώ και πολλά χρόνια από τότε που εμφανίστηκε το with encryption option (ούτε καν θυμάμαι από πότε) το κάνει με το να εφαρμόσει bitwise OR στο κείμενο του κώδικα.

Αυτό σημαίνει ότι όποιος χρήστης έχει δικαιώματα VIEW DEFINITION μπορεί να δει τον κώδικα μιας encrypted stored procedure κλπ, αρκεί να εκτελέσει μια άλλη sp που κάνει decrypt το περιεχόμενο της.

Αν ψάξετε στο internet θα βρείτε πολλές. Απλά σας παραθέτω μία που τυχαία τσίμπησα από τα msdn forums και η οποία δουλεύει σε SQL Server 2008 R2, αλλά μόνο για stored procedures.

ShowDecrypted Stored Procedure
 CREATE PROCEDURE dbo.ShowDecrypted(@ProcName SYSNAME = NULL)
AS
SET NOCOUNT ON
IF EXISTS 
(
SELECT * FROM sys.dm_exec_connections ec JOIN sys.endpoints e 
on (ec.[endpoint_id]=e.[endpoint_id]) 
WHERE e.[name]='Dedicated Admin Connection' 
AND ec.[session_id] = @@SPID
)
    BEGIN
 
    DECLARE @i BIGINT,@a NVARCHAR(MAX),@b NVARCHAR(MAX),@d NVARCHAR(MAX),@c NVARCHAR(MAX)
    SET @a=(SELECT [imageval] FROM [sys].[sysobjvalues] WHERE [objid] = OBJECT_ID(@ProcName) and [valclass] = 1 and [subobjid] = 1)
    SET @b='ALTER PROCEDURE '+ @ProcName +' WITH ENCRYPTION AS '+REPLICATE('-', 8000)
 
        BEGIN TRANSACTION
            EXECUTE (@b)
            SET @c=(SELECT [imageval] FROM [sys].[sysobjvalues] WHERE [objid] = OBJECT_ID(@ProcName) and [valclass] = 1 and [subobjid] = 1)    
        ROLLBACK TRANSACTION
 
    SET @d = REPLICATE(N'A', (DATALENGTH(@a) /2 ))
    SET @i=1
    WHILE @i<=(DATALENGTH(@a)/2)
    BEGIN
    SET @d = STUFF(@d, @i, 1,NCHAR(UNICODE(SUBSTRING(@a, @i, 1)) ^(UNICODE(SUBSTRING('CREATE PROCEDURE '+ @ProcName +' WITH ENCRYPTION AS ' + REPLICATE('-', 8000), @i, 1)) ^UNICODE(SUBSTRING(@c, @i, 1)))))
    SET @i=@i+1
    END
 
    SELECT @d [StoredProcedure]
 
    END
    ELSE
    BEGIN
        PRINT 'Use a DAC Connection'
    END
 
SET QUOTED_IDENTIFIER OFF
GO
SET ANSI_NULLS ON
GO
 

/*antonch*/

Antonios Chatzipavlis

Antonios is a Data Solutions Consultant and Trainer. He has been working in IT since 1988. In his career, he has worked as senior developer, IT Manager, Solutions Architect and IT Consultant. Since 1995 he has been devoted on new technologies and software development tools, mainly by Microsoft, either by training company staff and colleagues or assisting them in design, development and implementation as a consultant or chief developer. He has focused in Databases and Data Science since 1995. He specialized in Microsoft SQL Server since version 6.0 in areas like SQL Server Internals, Database Design and Development, Business Intelligence and in 2010 he has started working with Azure Data Platform, NoSQL databases, Big Data Technologies and Machine Learning. He is an active member of many IT communities in Greece, answering colleagues' questions and writing articles in his web site. He is the owner of SQLschool.gr which is a community portal with a lot of information about Microsoft SQL Server. He has been a Microsoft Certified Trainer (MCT) since 2000. Microsoft honored him as MVP on Data Platform due to his activities in SQL Server since 2010. He holds a large number of Microsoft Certifications and Microsoft SQL Server Certifications since version 6.5.