SQL server encryption – Symmetric Keys

In the previous blog we learnt about encryption and a brief about the SQL server option provided for data protection through encryption. 

http://sqlandmorewithkruti.blogspot.com/2015/10/sql-server-encryption.html

In this blog we will learn with a demo how to use the first option Symmetric Keys for encryption.As stated earlier symmetric keys use the same key to encrypt and decrypt data.

When a symmetric key is created, the symmetric key must be encrypted by using at least one of the following: certificate, password, symmetric key, asymmetric key, or PROVIDER. 

In this blog we will be using one protected with password.  In later modules we will be using asymmetric keys and certificates

1) Create Database Master Key

2) Encrypt Data

• Create Symmetric Key
• Open Key
• Encrypt Data
• Close Key

3) Decrypt Data

• Open Key
• Dencrypt Data
• Close Key

 1)  Create Database  Master Key

USE TESTDB;

GO

CREATE MASTER KEY ENCRYPTION BY PASSWORD = '1211!pwD##';

GO

2) Encrypt Data

I have a table with the below structure

CREATE TABLE [dbo].[BankDemo1](

            [BankID] [tinyint] NOT NULL,

            [BankName] [varchar](10) NOT NULL,

                                [BankAmt] [varchar](10) NOT NULL,

 CONSTRAINT [PK_BankDemo1] PRIMARY KEY CLUSTERED

(

            [BankID] ASC

)

) ON [PRIMARY]

BankID	BankName	BankAmt
1	abc	1000
2	def	2000
3	hij	3000

We shall be encrypting the [BankAmt] column. But the cipher data generated during encryption can only be of type varbinary. So the first step is for us to change the structure of the table.

USE TESTDB;

GO

ALTER TABLE BankDemo1

ADD BankAmtSymKey varbinary(MAX) NULL

GO

               

Now that our table schema is modified we proceed with creation of the symmetric key

Syntax : https://msdn.microsoft.com/en-us/library/ms188357.aspx

USE TESTDB;

GO

CREATE SYMMETRIC KEY TestSymmKey

WITH ALGORITHM = AES_256

ENCRYPTION BY PASSWORD = '1211!pwD##';

GO

Let’s do the trick!!!

USE TESTDB

GO

 -- Open the symmetric key

OPEN SYMMETRIC KEY TestSymmKey

DECRYPTION BY PASSWORD = '1211!pwD##';

 --Encrypt Data

GO

UPDATE BankDemo1

SET BankAmtSymKey = ENCRYPTBYKEY (Key_GUID('TestSymmKey'),BankAmt)

GO

 -- Close the symmetric key

CLOSE SYMMETRIC KEY TestSymmKey;

GO

Let’s see the magic we created!!!

BankID	BankName	BankAmtSymKey
1	Abc	0x00F5998B8C856F4E92697DBA96BD44AD01000000547D8E1730 DEF80FF7B2055C8478DA0DDCF7FCAC8E1C23B9C3E7F4A9D1712F75
2	Def	0x00F5998B8C856F4E92697DBA96BD44AD0100000015C40BFAD6 2718186D1EC41375B167FE96C96CB177F8A171C2C81E48E171D1C9
3	Hij	0x00F5998B8C856F4E92697DBA96BD44AD01000000738A3FA8152 E5CD66335CF2231B37BD5FBFD94BECD0CF056389E6614E5E40037

  

In the current example have saved both the text prior to encryption under the [BankAmt] column and the cipher text in [BankAmtSymKey] column. 

In practical scenarios it’s obvious to use a mechanism like stored procedures to perform the encryption task. This stored procedure would ideally taking inputs for data to encrypt and storing only the cipher text in the table.

3) Dencrypt Data

Well since we used ENCRYPTBYKEY function your guess is right we will use the corresponding DENCRYPTBYKEY function to retrieve the data.

USE TESTDB

GO

 -- Open the symmetric key

OPEN SYMMETRIC KEY TestSymmKey

DECRYPTION BY PASSWORD = '1211!pwD##';

GO

-- Decrypt Data

SELECT BankID,BankName,

CONVERT(varchar, DecryptByKey(BankAmtSymKey)) AS 'Decrypted Amount'

FROM BankDemo1

 -- Close the symmetric key

CLOSE SYMMETRIC KEY TestSymmKey;

GO

In the next blog we shall see the same example but this time we shall be using asymmetric keys.