DECRYPTBYKEY (Transact-SQL)
Applies to:
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
This function uses a symmetric key to decrypt data.
Transact-SQL syntax conventions
Note
This syntax is not supported by serverless SQL pool in Azure Synapse Analytics.
For dedicated SQL pools in Azure Synapse Analytics, result set caching should not be used in conjunction with DECRYPTBYKEY. If this cryptographic function must be used, ensure you have result set caching disabled (either at session-level or database-level) at the time of execution.
Syntax
DecryptByKey ( { 'ciphertext' | @ciphertext }
[ , add_authenticator, { authenticator | @authenticator } ] )
Note
To view Transact-SQL syntax for SQL Server 2014 (12.x) and earlier versions, see Previous versions documentation.
Arguments
ciphertext
A variable of type varbinary containing data encrypted with the key.
@ciphertext
A variable of type varbinary containing data encrypted with the key.
add_authenticator
Indicates whether the original encryption process included, and encrypted, an authenticator together with the plaintext. Must match the value passed to ENCRYPTBYKEY (Transact-SQL) during the data encryption process. add_authenticator has an int data type.
authenticator
The data used as the basis for the generation of the authenticator. Must match the value supplied to ENCRYPTBYKEY (Transact-SQL). authenticator has a sysname data type.
@authenticator
A variable containing data from which an authenticator generates. Must match the value supplied to ENCRYPTBYKEY (Transact-SQL). @authenticator has a sysname data type.
Return Types
varbinary, with a maximum size of 8,000 bytes. DECRYPTBYKEY
returns NULL if the symmetric key used for data encryption is not open or if ciphertext is NULL.
Remarks
DECRYPTBYKEY
uses a symmetric key. The database must have this symmetric key already open. DECRYPTBYKEY
will allow multiple keys open at the same time. You do not have to open the key immediately before cipher text decryption.
Symmetric encryption and decryption typically operates relatively quickly, and it works well for operations involving large data volumes.
The DECRYPTBYKEY
call must happen in the context of the database containing the encryption key. Ensure this by calling DECRYPTBYKEY
from an object (such as a view, or stored procedure, or function) that resides in the database.
Permissions
The symmetric key must already be open in the current session. See OPEN SYMMETRIC KEY (Transact-SQL) for more information.
Examples
A. Decrypting by using a symmetric key
This example decrypts ciphertext with a symmetric key.
-- First, open the symmetric key with which to decrypt the data.
OPEN SYMMETRIC KEY SSN_Key_01
DECRYPTION BY CERTIFICATE HumanResources037;
GO
-- Now list the original ID, the encrypted ID, and the
-- decrypted ciphertext. If the decryption worked, the original
-- and the decrypted ID will match.
SELECT NationalIDNumber, EncryptedNationalID
AS 'Encrypted ID Number',
CONVERT(nvarchar, DecryptByKey(EncryptedNationalID))
AS 'Decrypted ID Number'
FROM HumanResources.Employee;
GO
B. Decrypting by using a symmetric key and an authenticating hash
This example decrypts data originally encrypted together with an authenticator.
-- First, open the symmetric key with which to decrypt the data
OPEN SYMMETRIC KEY CreditCards_Key11
DECRYPTION BY CERTIFICATE Sales09;
GO
-- Now list the original card number, the encrypted card number,
-- and the decrypted ciphertext. If the decryption worked,
-- the original number will match the decrypted number.
SELECT CardNumber, CardNumber_Encrypted
AS 'Encrypted card number', CONVERT(nvarchar,
DecryptByKey(CardNumber_Encrypted, 1 ,
HashBytes('SHA1', CONVERT(varbinary, CreditCardID))))
AS 'Decrypted card number' FROM Sales.CreditCard;
GO
C. Fail to decrypt when not in the context of database with key
The following example demonstrates that DECRYPTBYKEY
must be executed in the context of the database that contains the key. The row will not be decrypted when DECRYPTBYKEY
is executed in the Master database; the result is NULL.
-- Create the database
CREATE DATABASE TestingDecryptByKey
GO
USE [TestingDecryptByKey]
-- Create the table and view
CREATE TABLE TestingDecryptByKey.dbo.Test(val VARBINARY(8000) NOT NULL);
GO
CREATE VIEW dbo.TestView AS SELECT CAST(DecryptByKey(val) AS VARCHAR(30)) AS DecryptedVal FROM TestingDecryptByKey.dbo.Test;
GO
-- Create the key, and certificate
USE TestingDecryptByKey;
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'ItIsreallyLong1AndSecured!Passsword#';
CREATE CERTIFICATE TestEncryptionCertificate WITH SUBJECT = 'TestEncryption';
CREATE SYMMETRIC KEY TestEncryptSymmmetricKey WITH ALGORITHM = AES_256, IDENTITY_VALUE = 'It is place for test',
KEY_SOURCE = 'It is source for test' ENCRYPTION BY CERTIFICATE TestEncryptionCertificate;
-- Insert rows into the table
DECLARE @var VARBINARY(8000), @Val VARCHAR(30);
SELECT @Val = '000-123-4567';
OPEN SYMMETRIC KEY TestEncryptSymmmetricKey DECRYPTION BY CERTIFICATE TestEncryptionCertificate;
SELECT @var = EncryptByKey(Key_GUID('TestEncryptSymmmetricKey'), @Val);
SELECT CAST(DecryptByKey(@var) AS VARCHAR(30)), @Val;
INSERT INTO dbo.Test VALUES(@var);
GO
-- Switch to master
USE [Master];
GO
-- Results show the date inserted
SELECT DecryptedVal FROM TestingDecryptByKey.dbo.TestView;
-- Results are NULL because we are not in the context of the TestingDecryptByKey Database
SELECT CAST(DecryptByKey(val) AS VARCHAR(30)) AS DecryptedVal FROM TestingDecryptByKey.dbo.Test;
GO
-- Clean up resources
USE TestingDecryptByKey;
DROP SYMMETRIC KEY TestEncryptSymmmetricKey REMOVE PROVIDER KEY;
DROP CERTIFICATE TestEncryptionCertificate;
Use [Master]
DROP DATABASE TestingDecryptByKey;
GO
See Also
ENCRYPTBYKEY (Transact-SQL)
CREATE SYMMETRIC KEY (Transact-SQL)
ALTER SYMMETRIC KEY (Transact-SQL)
DROP SYMMETRIC KEY (Transact-SQL)
Encryption Hierarchy
Choose an Encryption Algorithm