One of the encryption options in SQL Server is symmetric key encryption. This is the type of encryption most people think about when they consider encrypting data. In symmetric key encryption, we use a key to encrypt data, and then also use a key to decrypt data.

The key used for encryption and decryption is the same in Symmetric Key Encryption. This is why we call this symmetric. Just like with a house lock,

the key that locks (encrypts) also unlocks (decrypts). This is a picture of my front door and the lock uses a single key.

In SQL Server, we create a symmetric key and use that to encrypt data and also decrypt it. Here’s a simple example:

DECLARE @plain VARCHAR(200), @cipher VARBINARY(5000), @decrypt VARCHAR(200)

SELECT @plain = 'This is the plain text.'

-- encrypt
SELECT @cipher = ENCRYPTBYKEY(key_guid('MyFirstSymKey'),cast(@plain as NVARCHAR(200)));

SELECT 'Plain' = @plain
     , 'Cipher' = @cipher

-- decrypt
SELECT @decrypt = CAST( DECRYPTBYKEY(@cipher) AS nVARCHAR(200))

SELECT 'Plain' = @plain
     , 'Cipher' = @cipher
     , 'decrypt' = @decrypt

That’s it. If you run it, you see the original text, the encrypted text, and the decrypted text.

In another post, I’ll go into more options that are available for symmetric key encryption.