Signing Stored Procedures with a Certificate

Article
12/03/2008

New: 12 December 2006

This tutorial illustrates signing stored procedures using a certificate generated by SQL Server.

Note

To run the code in this tutorial you must have both Mixed Mode security configured and the AdventureWorks database installed. For more information about Mixed Mode security, see Authentication Mode. For more information about installing the AdventureWorks database, see Installing AdventureWorks Sample Databases and Samples.

Scenario

Signing stored procedures using a certificate is useful when you want to require permissions on the stored procedure but you do not want to explicitly grant a user those rights. Although you can accomplish this task in other ways, such as using the EXECUTE AS statement, using a certificate allows you to use a trace to find the original caller of the stored procedure. This provides a high level of auditing, especially during security or Data Definition Language (DDL) operations.

You can create a certificate in the master database to allow server-level permissions, or you can create a certificate in any user databases to allow database-level permissions. In this scenario, a user with no rights to base tables must access a stored procedure in the AdventureWorks database, and you want to audit the object access trail. Rather than using other ownership chain methods, you will create a server and database user account with no rights to the base objects, and a database user account with rights to a table and a stored procedure. Both the stored procedure and the second database user account will be secured with a certificate. The second database account will have access to all objects, and grant access to the stored procedure to the first database user account.

In this scenario you will first create a database certificate, a stored procedure, and a user, and then you will test the process following these steps:

Configure the environment.
Create a certificate.
Create and sign a stored procedure using the certificate.
Create a certificate account using the certificate.
Grant the certificate account database rights.
Display the access context.
Reset the environment.

Each code block in this example is explained in line. To copy the complete example, see Complete Example at the end of this tutorial.

1. Configure the Environment

To set the initial context of the example, in SQL Server Management Studio open a new Query and run the following code to open the AdventureWorks database. This code changes the database context to AdventureWorks and creates a new server login and database user account (TestCreditRatingUser), using a password.

USE AdventureWorks;
GO
-- Set up a login for the test user
CREATE LOGIN TestCreditRatingUser
   WITH PASSWORD = 'ASDECd2439587y'
GO
CREATE USER TestCreditRatingUser
FOR LOGIN TestCreditRatingUser;
GO

For more information on the CREATE USER statement, see CREATE USER (Transact-SQL). For more information on the CREATE LOGIN statement, see CREATE LOGIN (Transact-SQL).

2. Create a Certificate

You can create certificates in the server using the master database as the context, using a user database, or both. There are multiple options for securing the certificate. For more information on certificates, see CREATE CERTIFICATE (Transact-SQL).

Run this code to create a database certificate and secure it using a password.

CREATE CERTIFICATE TestCreditRatingCer
   ENCRYPTION BY PASSWORD = 'pGFD4bb925DGvbd2439587y'
      WITH SUBJECT = 'Credit Rating Records Access', 
      EXPIRY_DATE = '12/05/2010';
GO

3. Create and Sign a Stored Procedure Using the Certificate

Use the following code to create a stored procedure that selects data from the Vendor table in the Purchasing database schema, restricting access to only the companies with a credit rating of 1. Note that the first section of the stored procedure displays the context of the user account running the stored procedure, which is to demonstrate the concepts only. It is not required to satisfy the requirements.

CREATE PROCEDURE TestCreditRatingSP
AS
BEGIN
   -- Show who is running the stored procedure
   SELECT SYSTEM_USER 'system Login'
   , USER AS 'Database Login'
   , NAME AS 'Context'
   , TYPE
   , USAGE 
   FROM sys.user_token   

   -- Now get the data
   SELECT AccountNumber, Name, CreditRating 
   FROM Purchasing.Vendor
   WHERE CreditRating = 1
END
GO

Run this code to sign the stored procedure with the database certificate, using a password.

ADD SIGNATURE TO TestCreditRatingSP 
   BY CERTIFICATE TestCreditRatingCer
    WITH PASSWORD = 'pGFD4bb925DGvbd2439587y';
GO

For more information on stored procedures, see Stored Procedures (Database Engine).

For more information on database schemas, see Schemas.

For more information on signing stored procedures, see ADD SIGNATURE (Transact-SQL).

4. Create a Certificate Account Using the Certificate

Run this code to create a database user (TestCreditRatingcertificateAccount) from the certificate. This account has no server login, and will ultimately control access to the underlying tables.

USE AdventureWorks;
GO
CREATE USER TestCreditRatingcertificateAccount
   FROM CERTIFICATE TestCreditRatingCer;
GO

5. Grant the Certificate Account Database Rights

Run this code to grant TestCreditRatingcertificateAccount rights to the base table and the stored procedure.

GRANT SELECT 
   ON Purchasing.Vendor 
   TO TestCreditRatingcertificateAccount;
GO

GRANT EXECUTE 
   ON TestCreditRatingSP 
   TO TestCreditRatingcertificateAccount;
GO

For more information on granting permissions to objects, see GRANT (Transact-SQL).

6. Display the Access Context

To display the rights associated with the stored procedure access, run the following code to grant the rights to run the stored procedure to the TestCreditRatingUser user.

GRANT EXECUTE 
   ON TestCreditRatingSP 
   TO TestCreditRatingUser;
GO

Next, run the following code to run the stored procedure as the dbo login you used on the server. Observe the output of the user context information. It will show the dbo account as the context with its own rights and not through a group membership.

EXECUTE TestCreditRatingSP;
GO

Run the following code to use the EXECUTE AS statement to become the TestCreditRatingUser account and run the stored procedure. This time you will see the user context is set to the USER MAPPED TO CERTIFICATE context.

EXECUTE AS LOGIN = 'TestCreditRatingUser';
GO
EXECUTE TestCreditRatingSP;
GO

This shows you the auditing available because you signed the stored procedure.

Note

You have two ways of allowing a user to switch contexts within a database: SETUSER or EXECUTE AS. For more information about switching context, see EXECUTE AS vs. SETUSER.

7. Reset the Environment

The following code uses the REVERT statement to return the context of the current account to dbo, and resets the environment.

REVERT;
GO
DROP PROCEDURE TestCreditRatingSP;
GO
DROP USER TestCreditRatingcertificateAccount;
GO
DROP USER TestCreditRatingUser;
GO
DROP LOGIN TestCreditRatingUser;
GO
DROP CERTIFICATE TestCreditRatingCer;
GO

For more information about the REVERT statement, see REVERT (Transact-SQL).

Complete Example

This section displays the complete example code.

/* Step 1 - Open the AdventureWorks database */
USE AdventureWorks;
GO
-- Set up a login for the test user
CREATE LOGIN TestCreditRatingUser
   WITH PASSWORD = 'ASDECd2439587y'
GO
CREATE USER TestCreditRatingUser
FOR LOGIN TestCreditRatingUser;
GO

/* Step 2 - Create a certificate in the AdventureWorks database */
CREATE CERTIFICATE TestCreditRatingCer
   ENCRYPTION BY PASSWORD = 'pGFD4bb925DGvbd2439587y'
      WITH SUBJECT = 'Credit Rating Records Access', 
      EXPIRY_DATE = '12/05/2010';
GO

/* Step 3 - Create a stored procedure and
sign it using the certificate */
CREATE PROCEDURE TestCreditRatingSP
AS
BEGIN
   -- Shows who is running the stored procedure
   SELECT SYSTEM_USER 'system Login'
   , USER AS 'Database Login'
   , NAME AS 'Context'
   , TYPE
   , USAGE 
   FROM sys.user_token   

   -- Now get the data
   SELECT AccountNumber, Name, CreditRating 
   FROM Purchasing.Vendor
   WHERE CreditRating = 1
END
GO

ADD SIGNATURE TO TestCreditRatingSP 
   BY CERTIFICATE TestCreditRatingCer
    WITH PASSWORD = 'pGFD4bb925DGvbd2439587y';
GO

/* Step 4 - Create a database user for the certificate. 
This user has the ownership chain associated with it. */
USE AdventureWorks;
GO
CREATE USER TestCreditRatingcertificateAccount
   FROM CERTIFICATE TestCreditRatingCer;
GO

/* Step 5 - Grant the user database rights */
GRANT SELECT 
   ON Purchasing.Vendor 
   TO TestCreditRatingcertificateAccount;
GO

GRANT EXECUTE
   ON TestCreditRatingSP 
   TO TestCreditRatingcertificateAccount;
GO

/* Step 6 - Test, using the EXECUTE AS statement */
GRANT EXECUTE 
   ON TestCreditRatingSP 
   TO TestCreditRatingUser;
GO

-- Run the procedure as the dbo user, notice the output for the type
EXEC TestCreditRatingSP;
GO

EXECUTE AS LOGIN = 'TestCreditRatingUser';
GO
EXEC TestCreditRatingSP;
GO

/* Step 7 - Clean up the example */
REVERT;
GO
DROP PROCEDURE TestCreditRatingSP;
GO
DROP USER TestCreditRatingcertificateAccount;
GO
DROP USER TestCreditRatingUser;
GO
DROP LOGIN TestCreditRatingUser;
GO
DROP CERTIFICATE TestCreditRatingCer;
GO