AES_DECRYPT(crypt_str,key_str[,init_vector])

This function decrypts data using the official AES (Advanced Encryption Standard) algorithm. For more information, see the description of AES_ENCRYPT().

The optional initialization vector argument, init_vector. Statements that use AES_DECRYPT() are unsafe for statement-based replication.

AES_ENCRYPT(str,key_str[,init_vector])

AES_ENCRYPT() and AES_DECRYPT() implement encryption and decryption of data using the official AES (Advanced Encryption Standard) algorithm, previously known as “Rijndael.” The AES standard permits various key lengths. By default these functions implement AES with a 128-bit key length. Key lengths of 196 or 256 bits can be used, as described later. The key length is a trade off between performance and security.

AES_ENCRYPT() encrypts the string str using the key string key_str and returns a binary string containing the encrypted output. AES_DECRYPT() decrypts the encrypted string crypt_str using the key string key_str and returns the original plaintext string. If either function argument is NULL, the function returns NULL.

The str and crypt_str arguments can be any length, and padding is automatically added to str so it is a multiple of a block as required by block-based algorithms such as AES. This padding is automatically removed by the AES_DECRYPT() function. The length of crypt_str can be calculated using this formula:

16 * (trunc(string_length / 16) + 1)

For a key length of 128 bits, the most secure way to pass a key to the key_str argument is to create a truly random 128-bit value and pass it as a binary value. For example:

INSERT INTO t
VALUES (1,AES_ENCRYPT('text',UNHEX('F3229A0B371ED2D9441B830D21A390C3')));

A passphrase can be used to generate an AES key by hashing the passphrase. For example:

INSERT INTO t
VALUES (1,AES_ENCRYPT('text', UNHEX(SHA2('My secret passphrase',512))));

Do not pass a password or passphrase directly to crypt_str, hash it first. Previous versions of this documentation suggested the former approach, but it is no longer recommended as the examples shown here are more secure.

If AES_DECRYPT() detects invalid data or incorrect padding, it returns NULL. However, it is possible for AES_DECRYPT() to return a non-NULL value (possibly garbage) if the input data or the key is invalid.

AES_ENCRYPT() and AES_DECRYPT() permit control of the block encryption mode and take an optional init_vector initialization vector argument:

For modes that require the optional init_vector argument, it must be 16 bytes or longer (bytes in excess of 16 are ignored). An error occurs if init_vector is missing.

For modes that do not require init_vector, it is ignored and a warning is generated if it is specified.

A random string of bytes to use for the initialization vector can be produced by calling RANDOM_BYTES(16). For encryption modes that require an initialization vector, the same vector must be used for encryption and decryption.

mysql> SET block_encryption_mode = 'aes-256-cbc';
mysql> SET @key_str = SHA2('My secret passphrase',512);
mysql> SET @init_vector = RANDOM_BYTES(16);
mysql> SET @crypt_str = AES_ENCRYPT('text',@key_str,@init_vector);
mysql> SELECT AES_DECRYPT(@crypt_str,@key_str,@init_vector);
+-----------------------------------------------+
| AES_DECRYPT(@crypt_str,@key_str,@init_vector) |
+-----------------------------------------------+
| text                                          |
+-----------------------------------------------+

The following table lists each permitted block encryption mode, the SSL libraries that support it, and whether the initialization vector argument is required.

Statements that use AES_ENCRYPT() or AES_DECRYPT() are unsafe for statement-based replication.

COMPRESS(string_to_compress)

Compresses a string and returns the result as a binary string. This function requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. The compressed string can be uncompressed with UNCOMPRESS().

mysql> SELECT LENGTH(COMPRESS(REPEAT('a',1000)));
        -> 21
mysql> SELECT LENGTH(COMPRESS(''));
        -> 0
mysql> SELECT LENGTH(COMPRESS('a'));
        -> 13
mysql> SELECT LENGTH(COMPRESS(REPEAT('a',16)));
        -> 15

The compressed string contents are stored the following way:

DECODE(crypt_str,pass_str)

This function was removed in MySQL 8.0.3.

Consider using AES_ENCRYPT() and AES_DECRYPT() instead.

DES_DECRYPT(crypt_str[,key_str])

This function was removed in MySQL 8.0.3.

Consider using AES_ENCRYPT() and AES_DECRYPT() instead.

DES_ENCRYPT(str[,{key_num|key_str}])

This function was removed in MySQL 8.0.3.

Consider using AES_ENCRYPT() and AES_DECRYPT() instead.

ENCODE(str,pass_str)

This function was removed in MySQL 8.0.3.

Consider using AES_ENCRYPT() and AES_DECRYPT() instead.

ENCRYPT(str[,salt])

This function was removed in MySQL 8.0.3. For one-way hashing, consider using SHA2() instead.

MD5(str)

Calculates an MD5 128-bit checksum for the string. The value is returned as a string of 32 hexadecimal digits, or NULL if the argument was NULL. The return value can, for example, be used as a hash key. See the notes at the beginning of this section about storing hash values efficiently.

The return value is a string in the connection character set.

If FIPS mode is enabled, MD5() returns NULL. See Section 6.5, “FIPS Support”.

mysql> SELECT MD5('testing');
        -> 'ae2b1fca515949e5d54fb22b8ed95575'

This is the “RSA Data Security, Inc. MD5 Message-Digest Algorithm.”

See the note regarding the MD5 algorithm at the beginning this section.

PASSWORD(str)

This function was removed in MySQL 8.0.11.

RANDOM_BYTES(len)

This function returns a binary string of len random bytes generated using the random number generator of the SSL library. Permitted values of len range from 1 to 1024. For values outside that range, RANDOM_BYTES() generates a warning and returns NULL.

RANDOM_BYTES() can be used to provide the initialization vector for the AES_DECRYPT() and AES_ENCRYPT() functions. For use in that context, len must be at least 16. Larger values are permitted, but bytes in excess of 16 are ignored.

RANDOM_BYTES() generates a random value, which makes its result nondeterministic. Consequently, statements that use this function are unsafe for statement-based replication.

SHA1(str), SHA(str)

Calculates an SHA-1 160-bit checksum for the string, as described in RFC 3174 (Secure Hash Algorithm). The value is returned as a string of 40 hexadecimal digits, or NULL if the argument was NULL. One of the possible uses for this function is as a hash key. See the notes at the beginning of this section about storing hash values efficiently. SHA() is synonymous with SHA1().

The return value is a string in the connection character set.

mysql> SELECT SHA1('abc');
        -> 'a9993e364706816aba3e25717850c26c9cd0d89d'

SHA1() can be considered a cryptographically more secure equivalent of MD5(). However, see the note regarding the MD5 and SHA-1 algorithms at the beginning this section.

SHA2(str, hash_length)

Calculates the SHA-2 family of hash functions (SHA-224, SHA-256, SHA-384, and SHA-512). The first argument is the plaintext string to be hashed. The second argument indicates the desired bit length of the result, which must have a value of 224, 256, 384, 512, or 0 (which is equivalent to 256). If either argument is NULL or the hash length is not one of the permitted values, the return value is NULL. Otherwise, the function result is a hash value containing the desired number of bits. See the notes at the beginning of this section about storing hash values efficiently.

The return value is a string in the connection character set.

mysql> SELECT SHA2('abc', 224);
        -> '23097d223405d8228642a477bda255b32aadbce4bda0b3f7e36c9da7'

This function works only if MySQL has been configured with SSL support. See Section 6.3, “Using Encrypted Connections”.

SHA2() can be considered cryptographically more secure than MD5() or SHA1().

STATEMENT_DIGEST(statement)

Given an SQL statement as a string, returns the statement digest hash value as a string in the connection character set, or NULL if the argument is NULL. The related STATEMENT_DIGEST_TEXT() function returns the normalized statement digest. For information about statement digesting, see Section 26.10, “Performance Schema Statement Digests and Sampling”.

Both functions use the MySQL parser to parse the statement. If parsing fails, an error occurs. The error message includes the parse error only if the statement is provided as a literal string.

The max_digest_length system variable determines the maximum number of bytes available to these functions for computing normalized statement digests.

mysql> SET @stmt = 'SELECT * FROM mytable WHERE cola = 10 AND colb = 20';
mysql> SELECT STATEMENT_DIGEST(@stmt);
+------------------------------------------------------------------+
| STATEMENT_DIGEST(@stmt)                                          |
+------------------------------------------------------------------+
| 3bb95eeade896657c4526e74ff2a2862039d0a0fe8a9e7155b5fe492cbd78387 |
+------------------------------------------------------------------+
mysql> SELECT STATEMENT_DIGEST_TEXT(@stmt);
+----------------------------------------------------------+
| STATEMENT_DIGEST_TEXT(@stmt)                             |
+----------------------------------------------------------+
| SELECT * FROM `mytable` WHERE `cola` = ? AND `colb` = ?  |
+----------------------------------------------------------+

STATEMENT_DIGEST_TEXT(statement)

Given an SQL statement as a string, returns the normalized statement digest as a string in the connection character set, or NULL if the argument is NULL. For additional discussion and examples, see the description of the related STATEMENT_DIGEST() function.

UNCOMPRESS(string_to_uncompress)

Uncompresses a string compressed by the COMPRESS() function. If the argument is not a compressed value, the result is NULL. This function requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL.

mysql> SELECT UNCOMPRESS(COMPRESS('any string'));
        -> 'any string'
mysql> SELECT UNCOMPRESS('any string');
        -> NULL

UNCOMPRESSED_LENGTH(compressed_string)

Returns the length that the compressed string had before being compressed.

mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT('a',30)));
        -> 30

VALIDATE_PASSWORD_STRENGTH(str)

Given an argument representing a plaintext password, this function returns an integer to indicate how strong the password is. The return value ranges from 0 (weak) to 100 (strong).

Password assessment by VALIDATE_PASSWORD_STRENGTH() is done by the validate_password component. If that component is not installed, the function always returns 0. For information about installing validate_password, see Section 6.4.3, “The Password Validation Component”. To examine or configure the parameters that affect password testing, check or set the system variables implemented by validate_password. See Section 6.4.3.2, “Password Validation Options and Variables”.

The password is subjected to increasingly strict tests and the return value reflects which tests were satisfied, as shown in the following table. In addition, if the validate_password.check_user_name system variable is enabled and the password matches the user name, VALIDATE_PASSWORD_STRENGTH() returns 0 regardless of how other validate_password system variables are set.