How do you use the DECRYPTBYKEY function to decrypt data encrypted by the ENCRYPTBYKEY function in SQL Server?
GraceDv
Posted by GraceDv
Last Updated: July 23, 2024
SQL Decrypt
In SQL Server, the DECRYPTBYKEY function is used to decrypt data that was previously encrypted using the ENCRYPTBYKEY function. To successfully use these functions, you'll need to follow a few steps. Here’s a general outline of the process: 1. Open the symmetric key. Before you can use the DECRYPTBYKEY function, you must open the symmetric key that you want to use for decryption. This is done with the OPEN SYMMETRIC KEY statement. 2. Use the DECRYPTBYKEY function to decrypt data. Once the key is open, you can then use DECRYPTBYKEY to decrypt your encrypted data. 3. Close the symmetric key. After you're done, it's a good practice to close the symmetric key with CLOSE SYMMETRIC KEY. Here's an example demonstrating the process:
Example Steps
1. Create a Database and Table: 
CREATE DATABASE EncryptionDemo;
   GO

   USE EncryptionDemo;
   GO

   CREATE TABLE SensitiveData (
       ID INT PRIMARY KEY,
       EncryptedValue VARBINARY(MAX)
   );
2. Create and Open a Symmetric Key: 
USE EncryptionDemo;

   -- Create a master key (if it doesn't already exist)
   CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'YourStrongPassword123!';
   GO

   -- Create a symmetric key
   CREATE SYMMETRIC KEY MySymmetricKey
       WITH ALGORITHM = AES_256
       ENCRYPTION BY PASSWORD = 'AnotherStrongPassword123!';
   GO

   -- Open the symmetric key
   OPEN SYMMETRIC KEY MySymmetricKey
       DECRYPTION BY PASSWORD = 'AnotherStrongPassword123!';
3. Encrypt Data: 
INSERT INTO SensitiveData (ID, EncryptedValue)
   VALUES (1, ENCRYPTBYKEY(KEY_GUID('MySymmetricKey'), 'Sensitive Information'));
4. Decrypt Data: 
-- Make sure to open the symmetric key before decryption
   OPEN SYMMETRIC KEY MySymmetricKey
       DECRYPTION BY PASSWORD = 'AnotherStrongPassword123!';

   SELECT 
       ID,
       CONVERT(VARCHAR, DECRYPTBYKEY(EncryptedValue)) AS DecryptedValue
   FROM 
       SensitiveData;

   -- Close the symmetric key after use
   CLOSE SYMMETRIC KEY MySymmetricKey;
Important Notes:
- Data Types: The data encrypted with ENCRYPTBYKEY is returned as a VARBINARY(MAX) data type. When decrypting, you must convert it to the appropriate data type (such as VARCHAR or NVARCHAR). - Key Management: Always consider security best practices for managing your keys, such as protecting your passwords and not exposing them in your scripts. - Opening and Closing Keys: Make sure to open the key before attempting to decrypt any data and close it afterward. Not doing so can lead to errors or unintended access. With these steps and precautions, you should be able to effectively encrypt and decrypt data using the ENCRYPTBYKEY and DECRYPTBYKEY functions in SQL Server.
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