passphrase

Is the passphrase that will be used to generate the key for decryption.

@passphrase

Is a variable of type nvarchar, char, varchar, or nchar that contains the passphrase that will be used to generate the key for decryption.

' ciphertext '

Is the ciphertext to be decrypted.

@ciphertext

Is a variable of type varbinary that contains the ciphertext. The maximum size is 8,000 bytes.

add_authenticator

Indicates whether an authenticator was encrypted together with the plaintext. Is 1 if an authenticator was used. int.

@add_authenticator

Indicates whether an authenticator was encrypted together with the plaintext. Is 1 if an authenticator was used. int.

authenticator

Is the authenticator data. sysname.

@authenticator

Is a variable that contains data from which to derive an authenticator.

varbinary with a maximum size of 8,000 bytes.

No permissions are required for executing this function.

Returns NULL if the wrong passphrase or authenticator information is used.

The passphrase is used to generate a decryption key, which will not be persisted.

If an authenticator was included when the ciphertext was encrypted, the authenticator must be provided at decryption time. If the authenticator value provided at decryption time does not match the authenticator value encrypted with the data, the decryption will fail.

The following example decrypts the record updated in EncryptByPassPhrase.

USE AdventureWorks;
-- Get the pass phrase from the user.
DECLARE @PassphraseEnteredByUser nvarchar(128);
SET @PassphraseEnteredByUser 
= 'A little learning is a dangerous thing!';

-- Decrypt the encrypted record.
SELECT CardNumber, CardNumber_EncryptedbyPassphrase 
    AS 'Encrypted card number', CONVERT(nvarchar,
    DecryptByPassphrase(@PassphraseEnteredByUser, CardNumber_EncryptedbyPassphrase, 1 
    , CONVERT(varbinary, CreditCardID)))
    AS 'Decrypted card number' FROM Sales.CreditCard 
    WHERE CreditCardID = '3681';
GO

Reference

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