Categories:: Encryption Functions

TRY_DECRYPT¶

A special version of DECRYPT that returns a NULL value if an error occurs during decryption.

See also:: ENCRYPT , ENCRYPT_RAW , DECRYPT , DECRYPT_RAW , TRY_DECRYPT_RAW

Syntax¶

TRY_DECRYPT( <value_to_decrypt> , <passphrase> ,
         [ [ <additional_authenticated_data> , ] <encryption_method> ]
       )

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Arguments¶

Required:

value_to_decrypt: The BINARY value to decrypt.
passphrase: The passphrase to use to encrypt/decrypt the data. The passphrase is a VARCHAR.

Optional:

additional_authenticated_data

Additional authenticated data (AAD) is additional data whose confidentiality and authenticity is assured during the decryption process. However, this AAD is not encrypted and is not included as a field in the returned value from the ENCRYPT or ENCRYPT_RAW function.

If AAD is passed to the encryption function (ENCRYPT or ENCRYPT_RAW), then the same AAD must be passed to the decryption function (DECRYPT or DECRYPT_RAW). If the AAD passed to the decryption function does not match the AAD passed to the encryption function, then decryption fails.

The difference between the AAD and the passphrase is that the passphrase is intended to be kept secret (otherwise, the encryption is essentially worthless) while the AAD can be left public. The AAD helps authenticate that a public piece of information and an encrypted value are associated with each other. The examples section in the ENCRYPT function includes an example showing the behavior when the AAD matches and the behavior when it doesn’t match.

For ENCRYPT_RAW and DECRYPT_RAW, the data type of the AAD should be BINARY. For ENCRYPT and DECRYPT, the data type of the AAD can be either VARCHAR or BINARY, and does not need to match the data type of the value that was encrypted.

AAD is supported only by AEAD-enabled encryption modes like GCM (default).

encryption_method

This string specifies the method to use for encrypting/decrypting the data. This string contains subfields:

<algorithm>-<mode> [ /pad: <padding> ]

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The algorithm is currently limited to:

'AES': When a passphrase is passed (e.g. to ENCRYPT), the function uses AES-256 encryption (256 bits). When a key is passed (e.g. to ENCRYPT_RAW), the function uses 128, 192, or 256-bit encryption, depending upon the key length.

The algorithm is case-insensitive.

The mode specifies which block cipher mode should be used to encrypt messages. The following table shows which modes are supported, and which of those modes support padding:

Mode	Padding	Description
`'ECB'`	Yes	Encrypt every block individually with the key. This mode is generally discouraged and is included only for compatibility with external implementations.
`'CBC'`	Yes	The encrypted block is XORed with the previous block.
`'GCM'`	No	Galois/Counter Mode is a high-performance encryption mode that is AEAD-enabled. AEAD additionally assures the authenticity and confidentiality of the encrypted data by generating an AEAD tag. Moreover, AEAD supports AAD (additional authenticated data).
`'CTR'`	No	Counter mode.
`'OFB'`	No	Output feedback. The ciphertext is XORed with the plaintext of a block.
`'CFB'`	No	Cipher feedback is a combination of OFB and CBC.

The mode is case-insensitive.

The padding specifies how to pad messages whose length is not a multiple of the block size. Padding is applicable only for ECB and CBC modes; padding is ignored for other modes. The possible values for padding are:

'PKCS': Uses PKCS5 for block padding.

'NONE': No padding. The user needs to take care of the padding when using ECB or CBC mode.

The padding is case-insensitive.

Default setting: 'AES-GCM'.

If the mode is not specified, GCM is used.

If the padding is not specified, PKCS is used.

Returns¶

Returns the decrypted value as a BINARY value or a NULL value if any runtime error occurs during decryption.

Usage Notes and Examples¶

See the DECRYPT function for the usage notes and examples.