Article
10/01/2010

DECRYPTBYKEYAUTOCERT (Transact-SQL)

Decrypts by using a symmetric key that is automatically decrypted with a certificate.

Topic link icon Transact-SQL Syntax Conventions

Syntax

DecryptByKeyAutoCert (cert_ID,cert_password 
    , { 'ciphertext' | @ciphertext }
  [ , { add_authenticator | @add_authenticator } 
  [ , { authenticator | @authenticator } ] ] )

Arguments

cert_ID
Is the ID of the certificate that is used to protect the symmetric key. cert_ID is int.
cert_password
Is the password that protects the private key of the certificate. Can be NULL if the private key is protected by the database master key. cert_password is varchar.
'ciphertext'
Is the data that was encrypted with the key. ciphertext is varbinary.
@ciphertext
Is a variable of type varbinary that contains data that was encrypted with the key.
add_authenticator
Indicates whether an authenticator was encrypted together with the plaintext. Must be the same value that is passed to EncryptByKey when encrypting the data.Is 1 if an authenticator was used. add_authenticator is int.
@add_authenticator
Indicates whether an authenticator was encrypted together with the plaintext. Must be the same value that is passed to EncryptByKey when encrypting the data.
authenticator
Is the data from which to generate an authenticator. Must match the value that was supplied to EncryptByKey. authenticator is sysname.
@authenticator
Is a variable that contains data from which to generate an authenticator. Must match the value that was supplied to EncryptByKey.

Return Types

varbinary with a maximum size of 8,000 bytes.

Remarks

DecryptByKeyAutoCert combines the functionality of OPEN SYMMETRIC KEY and DecryptByKey. In a single operation, it decrypts a symmetric key and uses that key to decrypt cipher text.

Permissions

Requires VIEW DEFINITION permission on the symmetric key and CONTROL permission on the certificate.

Examples

The following example shows how DecryptByKeyAutoCert can be used to simplify code that performs a decryption. This code should be run on a freshly installed copy of the AdventureWorks database.

--Create the keys and certificate.
USE AdventureWorks;
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'mzkvdlk979438teag$$ds987yghn)(*&4fdg^';
OPEN MASTER KEY DECRYPTION BY PASSWORD = 'mzkvdlk979438teag$$ds987yghn)(*&4fdg^';
CREATE CERTIFICATE HumanResources037 
   WITH SUBJECT = 'Sammamish HR', 
   EXPIRY_DATE = '10/31/2009';
CREATE SYMMETRIC KEY SSN_Key_01 WITH ALGORITHM = DES
    ENCRYPTION BY CERTIFICATE HumanResources037;
GO
----Add a column of encrypted data.
ALTER TABLE HumanResources.Employee
    ADD EncryptedNationalIDNumber varbinary(128); 
OPEN SYMMETRIC KEY SSN_Key_01
   DECRYPTION BY CERTIFICATE HumanResources037 ;
UPDATE HumanResources.Employee
SET EncryptedNationalIDNumber
    = EncryptByKey(Key_GUID('SSN_Key_01'), NationalIDNumber);
GO
--
--Close the key used to encrypt the data.
CLOSE SYMMETRIC KEY SSN_Key_01;
--
--There are two ways to decrypt the stored data.
--
--OPTION ONE, using DecryptByKey()
--1. Open the symmetric key
--2. Decrypt the data
--3. Close the symmetric key
OPEN SYMMETRIC KEY SSN_Key_01
   DECRYPTION BY CERTIFICATE HumanResources037;
SELECT NationalIDNumber, EncryptedNationalIDNumber  
    AS 'Encrypted ID Number',
    CONVERT(nvarchar, DecryptByKey(EncryptedNationalIDNumber)) 
    AS 'Decrypted ID Number'
    FROM HumanResources.Employee;
CLOSE SYMMETRIC KEY SSN_Key_01;
--
--OPTION TWO, using DecryptByKeyAutoCert()
SELECT NationalIDNumber, EncryptedNationalIDNumber 
    AS 'Encrypted ID Number',
    CONVERT(nvarchar, DecryptByKeyAutoCert ( cert_ID('HumanResources037') , NULL ,EncryptedNationalIDNumber)) 
    AS 'Decrypted ID Number'
    FROM HumanResources.Employee;

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