http://www.sqlservercentral.com/blogs/sqlserver365/2013/09/11/encryption-decryption-routine/

Printed 2014/07/24 10:22PM

Encryption Decryption Routine

By Chris McGowan, 2013/09/11

In this post we will look at a complete end to end routine for encrypting, storing, decrypting data in SQL Server and just how easy it is to set-up and maintain.  SQL Server encrypts data with a hierarchical encryption and key management infrastructure.  Each layer encrypts the layer below it by using a combination of certificates, asymmetric keys, and symmetric keys.  It is important to understand the different layers of protection, how they interact the performance overhead and best practices.  Books Online has a great visualisation of the SQL Server encryption hierarchy which I have included below.




Script

Below is the script used to create both the encryption / decryption routine and the equivalent routine without encryption.  You will need to Modify the below;

-- Change the database name below
USESQLServer365;

GO

-- Change the path to the database master key backup
OPEN MASTER KEY DECRYPTION BY PASSWORD = 'rZVb3DwZ8Vptc2#vm4wapspB';
BACKUP MASTER KEY TO FILE = 'C:\SQL\Backup\DatabaseMasterKeys\SQLServer365DatabaseMasterKey'
    ENCRYPTION BY PASSWORD = 'ratr7XgGGSJ5dM4QzAaXc8cj';

GO

-- Change the path to the certificate backup
BACKUP CERTIFICATE CertBankDetails TOFILE = 'C:\SQL\Backup\Certificates\CertBankDetails';
GO

/*
      -----------------------------------------------------------------
      Encryption / Decryption Routine
      -----------------------------------------------------------------
   
      For more SQL resources, check out SQLServer365.blogspot.com

      -----------------------------------------------------------------

      You may alter this code for your own purposes.
      You may republish altered code as long as you give due credit.
      You must obtain prior permission before blogging this code.

      THIS CODE AND INFORMATION ARE PROVIDED "AS IS"
    
      -----------------------------------------------------------------
*/
-- Set database context
USESQLServer365
GO
-- Create table
IF NOT EXISTS ( SELECT  1
                FROM    sys.objects
                WHERE   [object_id] =OBJECT_ID('dbo.BankDetails')
                        AND [type] = 'U' )
CREATE TABLE dbo.BankDetails(
      BankDetailsID INT IDENTITY(1,1) NOT NULL CONSTRAINT [PK_BankDetails:BankDetailsID] PRIMARY KEY,
      CustomerID INT NOT NULL,
      SortCode VARBINARY(128) NOT NULL,
      AccountNumber VARBINARY(128) NOT NULL,
      InsertDate DATETIME NOT NULL CONSTRAINT [DF_BankDetails:InsertDate] DEFAULT (GETDATE())
) ON [PRIMARY]
ELSE
      PRINT 'Error: Table "dbo.BankDetails" already exists, please modify the script to create a table name that does not already exist';
GO

-- Create database master key
/*
      This is the database master key that is used to encrypt all certificates when a password is not supplied
*/
IF NOT EXISTS ( SELECT 1
                        FROM sys.symmetric_keys
                        WHERE name = '##MS_DatabaseMasterKey##')
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'rZVb3DwZ8Vptc2#vm4wapspB'
ELSE
      PRINT 'Error: Database master key already exists!'
GO

-- Backup master key
OPEN MASTER KEY DECRYPTION BY PASSWORD = 'rZVb3DwZ8Vptc2#vm4wapspB';
BACKUP MASTER KEY TO FILE = 'C:\SQL\Backup\DatabaseMasterKeys\SQLServer365DatabaseMasterKey'
    ENCRYPTION BY PASSWORD = 'ratr7XgGGSJ5dM4QzAaXc8cj';
GO

-- Create certificate
/*
      This is the certificate used to protect the symmetric key
*/
IF NOT EXISTS ( SELECT  1
                FROM    sys.certificates
                WHERE   name = 'CertBankDetails' )
CREATE CERTIFICATE CertBankDetails
   WITH SUBJECT = 'Bank Details Certificate',
   EXPIRY_DATE = '02/25/2014';
ELSE
      PRINT 'Error: Certificate "CertBankDetails" already exists, please modify the script to create a certificate that does not already exist';
GO

-- Backup the certificate
BACKUP CERTIFICATE CertBankDetails TOFILE = 'C:\SQL\Backup\Certificates\CertBankDetails';
GO

-- Create symmetric key
/*
      This is the symmetric key used in conjunction with the certificate to encrypt / decrypt the data
*/
IF NOT EXISTS ( SELECT  1
                FROM    sys.symmetric_keys
                WHERE   name = 'SymKeyBankDetails' )
CREATE SYMMETRIC KEYSymKeyBankDetails
      WITH ALGORITHM= AES_256
    ENCRYPTION BY CERTIFICATECertBankDetails;
ELSE
      PRINT 'Error: Symmetric key "SymKeyBankDetails" already exists, please modify the script to create a symmetric key that does not already exist';
GO

-- Create Encryption Proc
IF EXISTS ( SELECT  1
            FROM    sys.objects
            WHERE   [object_id] =OBJECT_ID('dbo.spInsertBankDetails')
                    AND[type] IN ( 'P' ) )
    BEGIN
        DROP PROCEDURE dbo.spInsertBankDetails
    END
GO                   
CREATE PROCEDURE dbo.spInsertBankDetails
AS
BEGIN
-- Open Symetric Key
OPEN SYMMETRIC KEYSymKeyBankDetails
   DECRYPTION BY CERTIFICATECertBankDetails;
-- Insert a record
INSERT INTO SQLServer365.dbo.BankDetails
           (CustomerID,
           SortCode,
           AccountNumber,
           InsertDate)
     VALUES
           (1,
           EncryptByKey(Key_GUID('SymKeyBankDetails'), '01-02-03'), -- Encrypt SortCode
           EncryptByKey(Key_GUID('SymKeyBankDetails'), '01234567'), -- Encrypt AccountNumber
           GETDATE());
END
GO

-- Create Decryption Proc
IF EXISTS ( SELECT  1
            FROM    sys.objects
            WHERE   [object_id] =OBJECT_ID('dbo.spGetBankDetails')
                    AND[type] IN ( 'P' ) )
    BEGIN
        DROP PROCEDURE dbo.spGetBankDetails
    END
GO 
CREATE PROCEDURE dbo.spGetBankDetails
AS
BEGIN
-- Open Symetric Key
OPEN SYMMETRIC KEYSymKeyBankDetails
   DECRYPTION BY CERTIFICATECertBankDetails;
  
-- Return decrypted record
SELECTBankDetailsID,
      CustomerID,
      CONVERT(VARCHAR, DecryptByKey(SortCode)) AS SortCode, -- Decrypt SortCode
      CONVERT(VARCHAR, DecryptByKey(AccountNumber)) AS AccountNumber, -- Decrypt AccountNumber
      InsertDate
FROMSQLServer365.dbo.BankDetails;
END
GO

-- Insert an encrypted record
EXECSQLServer365.dbo.spInsertBankDetails;
GO

-- Return encrypted data
SELECTBankDetailsID,
      CustomerID,
      SortCode,
      AccountNumber,
      InsertDate
  FROMSQLServer365.dbo.BankDetails;
GO 
 
-- Return decrypted data
EXECSQLServer365.dbo.spGetBankDetails;
GO


/*
      Unencrypted data for performance comparison
*/

-- Set database context
USESQLServer365
GO
-- Create table
IF NOT EXISTS ( SELECT  1
                FROM    sys.objects
                WHERE   [object_id] =OBJECT_ID('dbo.BankDetailsNoEncryption')
                        AND [type] = 'U' )
CREATE TABLE dbo.BankDetailsNoEncryption(
      BankDetailsNoEncryptionID INT IDENTITY(1,1) NOT NULL CONSTRAINT[PK_BankDetailsNoEncryption:BankDetailsNoEncryptionID] PRIMARYKEY,
      CustomerID INT NOT NULL,
      SortCode VARCHAR(50) NOT NULL,
      AccountNumber VARCHAR(50) NOT NULL,
      InsertDate DATETIME NOT NULL CONSTRAINT [DF_BankDetailsNoEncryption:InsertDate] DEFAULT (GETDATE())
) ON [PRIMARY]
ELSE
      PRINT 'Error: Table "dbo.BankDetailsNoEncryption" already exists, please modify the script to create a table name that does not already exist';
GO

-- Create Insert Proc
IF EXISTS ( SELECT  1
            FROM    sys.objects
            WHERE   [object_id] =OBJECT_ID('dbo.spInsertBankDetailsNoEncryption')
                    AND[type] IN ( 'P' ) )
    BEGIN
        DROP PROCEDURE dbo.spInsertBankDetailsNoEncryption
    END
GO                   
CREATE PROCEDURE dbo.spInsertBankDetailsNoEncryption
AS
BEGIN
-- Insert a record
INSERT INTO SQLServer365.dbo.BankDetailsNoEncryption
           (CustomerID,
           SortCode,
           AccountNumber,
           InsertDate)
     VALUES
           (1,
           '01-02-03',
           '01234567',
           GETDATE());
END
GO

-- Create Get Proc
IF EXISTS ( SELECT  1
            FROM    sys.objects
            WHERE   [object_id] =OBJECT_ID('dbo.spGetBankDetailsNoEncryption')
                    AND[type] IN ( 'P' ) )
    BEGIN
        DROP PROCEDURE dbo.spGetBankDetailsNoEncryption
    END
GO 
CREATE PROCEDURE dbo.spGetBankDetailsNoEncryption
AS
    BEGIN
        SELECT  BankDetailsNoEncryptionID ,
                CustomerID ,
                SortCode ,
                AccountNumber InsertDate
        FROM    SQLServer365.dbo.BankDetailsNoEncryption;
    END
GO

-- Insert unencrypted record
EXECSQLServer365.dbo.spInsertBankDetailsNoEncryption;
GO

-- Return data
EXECSQLServer365.dbo.spGetBankDetailsNoEncryption;

GO

Performance Comparison

I did some performance analysis comparing the insert encrypting the data / the select decrypting the data to the equivalent without encryption and decryption.  I used SQLQueryStress by Adam Machanic to execute the insert and select of both routines 100 times across 10 threads, the results of which I have to say might surprise a few of you;


UnencryptedInsert
EncryptedInsert
IncreasePercentage
Execution Time
0.73
2.5712
252.22
Client Seconds / Iteration (Avg)
0.0055
0.022
300.00
Logical Reads / Iteration (Avg)
2.034
2.114
3.93
CPU Seconds / Iteration (Avg)
0.0002
0.0033
1550.00
Actual Seconds / Iteration (Avg)
0.0076
0.0288
278.95
UnencryptedSelect
EncryptedSelect
IncreasePercentage
Execution Time
0.582
3.7593
545.93
Client Seconds / Iteration (Avg)
0.0032
0.0267
734.38
Logical Reads / Iteration (Avg)
10
26
160.00
CPU Seconds / Iteration (Avg)
0.0012
0.0103
758.33
Actual Seconds / Iteration (Avg)
0.0017
0.0319
1776.47

With this significant overhead, I recommend you make sure you have the capacity to make use of SQL Servers encryption hierarchy.  It is important to be selective, only encrypt data that you actually need to.  Investigate the use of an Hardware Security Module (HSM) as these add a layer of abstraction by keeping the encryption keys separate from the the encrypted data.  It is also possible to offload the encryption overhead from the SQL Server to the HSM for improved performance.


I will finish with 3 recommendations;

Backup the certificates and keys!

Simple really, make sure you backup all your database master keys and all your certificates, the usual precautions apply here as they do for all backups;
Be aware of the expiry date of the certificates!

Again this goes without saying but you don't want the be the person responsible when the applications are throwing errors as the certificate has expired :)

Scripts Save Life's!

As I have said many times before, I'm not a GUI fan.  Each to their own but you really should be scripting this stuff!  Scripts can be saved, backed up, recovered and the end result is achieved quicker than a GUI or Wizard if you have the scripts to hand.

Enjoy!

Chris
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