MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
Table 12.18 Encryption Functions
Name | Description |
---|---|
AES_DECRYPT() |
Decrypt using AES |
AES_ENCRYPT() |
Encrypt using AES |
COMPRESS() |
Return result as a binary string |
DECODE() (deprecated) |
Decode a string encrypted using ENCODE() |
DES_DECRYPT() (deprecated) |
Decrypt a string |
DES_ENCRYPT() (deprecated) |
Encrypt a string |
ENCODE() (deprecated) |
Encode a string |
ENCRYPT() (deprecated) |
Encrypt a string |
MD5() |
Calculate MD5 checksum |
PASSWORD() (deprecated) |
Calculate and return a password string |
RANDOM_BYTES() |
Return a random byte vector |
SHA1() , SHA() |
Calculate an SHA-1 160-bit checksum |
SHA2() |
Calculate an SHA-2 checksum |
UNCOMPRESS() |
Uncompress a string compressed |
UNCOMPRESSED_LENGTH() |
Return the length of a string before compression |
VALIDATE_PASSWORD_STRENGTH() |
Determine strength of password |
Many encryption and compression functions return strings for which
the result might contain arbitrary byte values. If you want to
store these results, use a column with a
VARBINARY
or
BLOB
binary string data type. This
avoids potential problems with trailing space removal or character
set conversion that would change data values, such as may occur if
you use a nonbinary string data type
(CHAR
,
VARCHAR
,
TEXT
).
Some encryption functions return strings of ASCII characters:
MD5()
,
PASSWORD()
,
SHA()
,
SHA1()
,
SHA2()
. Their return value is a
string that has a character set and collation determined by the
character_set_connection
and
collation_connection
system
variables. This is a nonbinary string unless the character set is
binary
.
If an application stores values from a function such as
MD5()
or
SHA1()
that returns a string of hex
digits, more efficient storage and comparisons can be obtained by
converting the hex representation to binary using
UNHEX()
and storing the result in a
BINARY(
column. Each pair of hexadecimal digits requires one byte in
binary form, so the value of N
)N
depends
on the length of the hex string. N
is
16 for an MD5()
value and 20 for a
SHA1()
value. For
SHA2()
,
N
ranges from 28 to 32 depending on the
argument specifying the desired bit length of the result.
The size penalty for storing the hex string in a
CHAR
column is at least two times,
up to eight times if the value is stored in a column that uses the
utf8
character set (where each character uses 4
bytes). Storing the string also results in slower comparisons
because of the larger values and the need to take character set
collation rules into account.
Suppose that an application stores
MD5()
string values in a
CHAR(32)
column:
CREATE TABLE md5_tbl (md5_val CHAR(32), ...); INSERT INTO md5_tbl (md5_val, ...) VALUES(MD5('abcdef'), ...);
To convert hex strings to more compact form, modify the
application to use UNHEX()
and
BINARY(16)
instead as follows:
CREATE TABLE md5_tbl (md5_val BINARY(16), ...); INSERT INTO md5_tbl (md5_val, ...) VALUES(UNHEX(MD5('abcdef')), ...);
Applications should be prepared to handle the very rare case that a hashing function produces the same value for two different input values. One way to make collisions detectable is to make the hash column a primary key.
Exploits for the MD5 and SHA-1 algorithms have become known. You
may wish to consider using another one-way encryption function
described in this section instead, such as
SHA2()
.
Passwords or other sensitive values supplied as arguments to encryption functions are sent as cleartext to the MySQL server unless an SSL connection is used. Also, such values appear in any MySQL logs to which they are written. To avoid these types of exposure, applications can encrypt sensitive values on the client side before sending them to the server. The same considerations apply to encryption keys. To avoid exposing these, applications can use stored procedures to encrypt and decrypt values on the server side.
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()
.
Statements that use
AES_DECRYPT()
are unsafe for
statement-based replication and cannot be stored in the query
cache.
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:
The block_encryption_mode
system variable controls the mode for block-based
encryption algorithms. Its default value is
aes-128-ecb
, which signifies encryption
using a key length of 128 bits and ECB mode. For a
description of the permitted values of this variable, see
Section 5.1.7, “Server System Variables”.
The optional init_vector
argument provides an initialization vector for block
encryption modes that require it.
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.
Block Encryption Mode | SSL Libraries that Support Mode | Initialization Vector Required |
---|---|---|
ECB | OpenSSL, yaSSL | No |
CBC | OpenSSL, yaSSL | Yes |
CFB1 | OpenSSL | Yes |
CFB8 | OpenSSL | Yes |
CFB128 | OpenSSL | Yes |
OFB | OpenSSL | Yes |
Statements that use
AES_ENCRYPT()
or
AES_DECRYPT()
are unsafe for
statement-based replication and cannot be stored in the query
cache.
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:
Empty strings are stored as empty strings.
Nonempty strings are stored as a 4-byte length of the
uncompressed string (low byte first), followed by the
compressed string. If the string ends with space, an extra
.
character is added to avoid problems
with endspace trimming should the result be stored in a
CHAR
or
VARCHAR
column. (However,
use of nonbinary string data types such as
CHAR
or
VARCHAR
to store compressed
strings is not recommended anyway because character set
conversion may occur. Use a
VARBINARY
or
BLOB
binary string column
instead.)
DECODE()
decrypts the encrypted
string crypt_str
using
pass_str
as the password.
crypt_str
should be a string
returned from ENCODE()
.
The ENCODE()
and
DECODE()
functions are
deprecated in MySQL 5.7, and should no longer
be used. Expect them to be removed in a future MySQL
release. Consider using
AES_ENCRYPT()
and
AES_DECRYPT()
instead.
DES_DECRYPT(
crypt_str
[,key_str
])
Decrypts a string encrypted with
DES_ENCRYPT()
. If an error
occurs, this function returns NULL
.
This function works only if MySQL has been configured with SSL support. See Section 6.3, “Using Encrypted Connections”.
If no key_str
argument is given,
DES_DECRYPT()
examines the
first byte of the encrypted string to determine the DES key
number that was used to encrypt the original string, and then
reads the key from the DES key file to decrypt the message.
For this to work, the user must have the
SUPER
privilege. The key file
can be specified with the
--des-key-file
server option.
If you pass this function a key_str
argument, that string is used as the key for decrypting the
message.
If the crypt_str
argument does not
appear to be an encrypted string, MySQL returns the given
crypt_str
.
The DES_ENCRYPT()
and
DES_DECRYPT()
functions are
deprecated in MySQL 5.7, are removed in MySQL
8.0, and should no longer be used. Consider using
AES_ENCRYPT()
and
AES_DECRYPT()
instead.
DES_ENCRYPT(
str
[,{key_num
|key_str
}])
Encrypts the string with the given key using the Triple-DES algorithm.
This function works only if MySQL has been configured with SSL support. See Section 6.3, “Using Encrypted Connections”.
The encryption key to use is chosen based on the second
argument to DES_ENCRYPT()
, if
one was given. With no argument, the first key from the DES
key file is used. With a key_num
argument, the given key number (0 to 9) from the DES key file
is used. With a key_str
argument,
the given key string is used to encrypt
str
.
The key file can be specified with the
--des-key-file
server option.
The return string is a binary string where the first character
is CHAR(128 |
. If an error
occurs, key_num
)DES_ENCRYPT()
returns
NULL
.
The 128 is added to make it easier to recognize an encrypted
key. If you use a string key,
key_num
is 127.
The string length for the result is given by this formula:
new_len
=orig_len
+ (8 - (orig_len
% 8)) + 1
Each line in the DES key file has the following format:
key_num
des_key_str
Each key_num
value must be a number
in the range from 0
to
9
. Lines in the file may be in any order.
des_key_str
is the string that is
used to encrypt the message. There should be at least one
space between the number and the key. The first key is the
default key that is used if you do not specify any key
argument to DES_ENCRYPT()
.
You can tell MySQL to read new key values from the key file
with the FLUSH DES_KEY_FILE
statement. This requires the
RELOAD
privilege.
One benefit of having a set of default keys is that it gives applications a way to check for the existence of encrypted column values, without giving the end user the right to decrypt those values.
The DES_ENCRYPT()
and
DES_DECRYPT()
functions are
deprecated in MySQL 5.7, are removed in MySQL
8.0, and should no longer be used. Consider using
AES_ENCRYPT()
and
AES_DECRYPT()
instead.
mysql>SELECT customer_address FROM customer_table
>WHERE crypted_credit_card = DES_ENCRYPT('credit_card_number');
ENCODE()
encrypts
str
using
pass_str
as the password. The
result is a binary string of the same length as
str
. To decrypt the result, use
DECODE()
.
The ENCODE()
and
DECODE()
functions are
deprecated in MySQL 5.7, and should no longer
be used. Expect them to be removed in a future MySQL
release.
If you still need to use
ENCODE()
, a salt value must be
used with it to reduce risk. For example:
ENCODE('cleartext', CONCAT('my_random_salt','my_secret_password'))
A new random salt value must be used whenever a password is updated.
Encrypts str
using the Unix
crypt()
system call and returns a binary
string. The salt
argument must be a
string with at least two characters or else the result is
NULL
. If no salt
argument is given, a random value is used.
The ENCRYPT()
function is
deprecated in MySQL 5.7, are removed in MySQL
8.0, and should no longer be used. For one-way
hashing, consider using
SHA2()
instead.
mysql> SELECT ENCRYPT('hello');
-> 'VxuFAJXVARROc'
ENCRYPT()
ignores all but the
first eight characters of str
, at
least on some systems. This behavior is determined by the
implementation of the underlying crypt()
system call.
The use of ENCRYPT()
with the
ucs2
, utf16
,
utf16le
, or utf32
multibyte character sets is not recommended because the system
call expects a string terminated by a zero byte.
If crypt()
is not available on your
system (as is the case with Windows),
ENCRYPT()
always returns
NULL
.
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.
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.
This function is deprecated in MySQL 5.7 and is removed in MySQL 8.0.
Returns a hashed password string calculated from the cleartext
password str
. The return value is a
string in the connection character set, or
NULL
if the argument is
NULL
. This function is the SQL interface to
the algorithm used by the server to encrypt MySQL passwords
for storage in the mysql.user
grant table.
The old_passwords
system
variable controls the password hashing method used by the
PASSWORD()
function. It also
influences password hashing performed by
CREATE USER
and
GRANT
statements that specify a
password using an IDENTIFIED BY
clause.
The following table shows, for each password hashing method,
the permitted value of old_passwords
and
which authentication plugins use the hashing method.
Password Hashing Method | old_passwords Value | Associated Authentication Plugin |
---|---|---|
MySQL 4.1 native hashing | 0 | mysql_native_password |
SHA-256 hashing | 2 | sha256_password |
SHA-256 password hashing
(old_passwords=2
) uses a
random salt value, which makes the result from
PASSWORD()
nondeterministic.
Consequently, statements that use this function are not safe
for statement-based replication and cannot be stored in the
query cache.
Encryption performed by
PASSWORD()
is one-way (not
reversible), but it is not the same type of encryption used
for Unix passwords.
PASSWORD()
is used by the
authentication system in MySQL Server; you should
not use it in your own applications.
For that purpose, consider a more secure function such as
SHA2()
instead. Also see
RFC 2195,
section 2 (Challenge-Response Authentication Mechanism
(CRAM)), for more information about handling
passwords and authentication securely in your applications.
Under some circumstances, statements that invoke
PASSWORD()
may be recorded in
server logs or on the client side in a history file such as
~/.mysql_history
, which means that
cleartext passwords may be read by anyone having read access
to that information. For information about the conditions
under which this occurs for the server logs and how to
control it, see Section 6.1.2.3, “Passwords and Logging”. For
similar information about client-side logging, see
Section 4.5.1.3, “mysql Client Logging”.
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, an error occurs.
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 and cannot be stored in the query
cache.
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.
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()
.
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
plugin. If
that plugin is not installed, the function always returns 0.
For information about installing
validate_password
, see
Section 6.4.3, “The Password Validation Plugin”. 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 Plugin 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.
Password Test | Return Value |
---|---|
Length < 4 | 0 |
Length ≥ 4 and <
validate_password_length |
25 |
Satisfies policy 1 (LOW ) |
50 |
Satisfies policy 2 (MEDIUM ) |
75 |
Satisfies policy 3 (STRONG ) |
100 |