6.5.1.4 SHA-256 Pluggable Authentication

MySQL provides an authentication plugin that implements SHA-256 hashing for user account passwords.

Important

To connect to the server using an account that authenticates with the sha256_password plugin, you must use either an SSL connection or an unencrypted connection that encrypts the password using RSA, as described later in this section. Either way, use of the sha256_password plugin requires that MySQL be built with SSL capabilities. See Section 6.4, “Using Secure Connections”.

The following table shows the plugin names on the server and client sides.

Table 6.11 Plugin and Library Names for SHA-256 Authentication

Server-side plugin name	sha256_password
Client-side plugin name	sha256_password
Library file name	None (plugins are built in)

The following sections provide installation and usage information specific to SHA-256 pluggable authentication:

• Installing SHA-256 Pluggable Authentication

• Using sha256 Pluggable Authentication

For general information about pluggable authentication in MySQL, see Section 6.3.7, “Pluggable Authentication”.

Installing SHA-256 Pluggable Authentication

The sha256_password plugin exists in server and client forms:

• The server-side plugin is built into the server, need not be loaded explicitly, and cannot be disabled by unloading it.

• The client-side plugin is built into the libmysqlclient client library and available to any program linked against libmysqlclient.

Using sha256 Pluggable Authentication

To set up an account that uses the sha256_password plugin for SHA-256 password hashing, use the following procedure.

1. Create the account and specify that it authenticates using the sha256_password plugin:

   CREATE USER 'sha256user'@'localhost' IDENTIFIED WITH sha256_password;

2. Set the old_passwords system variable to 2 to cause the PASSWORD() function to use SHA-256 hashing of password strings, then set the account password:

   SET old_passwords = 2;
   SET PASSWORD FOR 'sha256user'@'localhost' = PASSWORD('Sh@256Pa33');

Alternatively, start the server with the default authentication plugin set to sha256_password. For example, put these lines in the server option file:

[mysqld]
default-authentication-plugin=sha256_password

That causes the sha256_password plugin to be used by default for new accounts. As a result, it is possible to create the account and set its password without naming the plugin explicitly using this CREATE USER syntax:

CREATE USER 'sha256user'@'localhost' IDENTIFIED BY 'Sh@256Pa33';

In this case, the server assigns the sha256_password plugin to the account and encrypts the password using SHA-256.

Accounts in the mysql.user table that use SHA-256 passwords can be identified as rows with 'sha256_password' in the plugin column and a SHA-256 password hash in the authentication_string column.

Another consequence of using sha256_password as the default authentication plugin is that to create an account that uses a different plugin, you must specify that plugin using an IDENTIFIED WITH clause in the CREATE USER statement, then set old_passwords appropriately for the plugin before using SET PASSWORD to set the account password. For example, to use the mysql_native_password plugin, do this:

CREATE USER 'nativeuser'@'localhost' IDENTIFIED WITH mysql_native_password;
SET old_passwords = 0;
SET PASSWORD FOR 'nativeuser'@'localhost' = PASSWORD('N@tivePa33');

To set or change the password for any account that authenticates using the sha256_password plugin, be sure that the value of old_passwords is 2 before using SET PASSWORD. If old_passwords has a value other than 2, an error occurs for attempts to set the password:

mysql> SET old_passwords = 0;
mysql> SET PASSWORD FOR 'sha256user'@'localhost' = PASSWORD('NewSh@256Pa33');
ERROR 1827 (HY000): The password hash doesn't have the expected format.
Check if the correct password algorithm is being used with the
PASSWORD() function.

For more information about old_passwords and PASSWORD(), see Section 5.1.5, “Server System Variables”, and Section 12.13, “Encryption and Compression Functions”.

MySQL can be compiled using either OpenSSL or yaSSL (see Section 6.4.1, “OpenSSL Versus yaSSL”). The sha256_password plugin works with distributions compiled using either package, but if MySQL is compiled using OpenSSL, RSA encryption is available and sha256_password implements the following additional capabilities. (To enable these capabilities, you must also follow the RSA configuration procedure given later in this section.)

• It is possible for the client to transmit passwords to the server using RSA encryption during the client connection process, as described later.

• The server exposes two additional system variables, sha256_password_private_key_path and sha256_password_public_key_path. It is intended that the database administrator will set these to the names of the RSA private and public key-pair files at server startup if the key files have names that differ from the system variable default values.

• The server exposes a status variable, Rsa_public_key, that displays the RSA public key value.

• The mysql and mysqltest client programs support a --server-public-key-path option for specifying an RSA public key file explicitly.

For clients that use the sha256_password plugin, passwords are never exposed as cleartext when connecting to the server. How password transmission occurs depends on whether an SSL connection is used and whether RSA encryption is available:

• If an SSL connection is used, the password is sent as cleartext but cannot be snooped because the connection is encrypted using SSL.

• If an SSL connection is not used but RSA encryption is available, the password is sent within an unencrypted connection, but the password is RSA-encrypted to prevent snooping. When the server receives the password, it decrypts it. A scramble is used in the encryption to prevent repeat attacks.

• If an SSL connection is not used and RSA encryption is not available, the sha256_password plugin causes the connection attempt to fail because the password cannot be sent without being exposed as cleartext.

As mentioned previously, RSA password encryption is available only if MySQL was compiled using OpenSSL. The implication for MySQL distributions compiled using yaSSL is that SHA-256 passwords can be used only when clients use SSL to access the server. See Section 6.4.4, “Configuring MySQL to Use Secure Connections”.

Assuming that MySQL has been compiled using OpenSSL, the following procedure describes how to enable RSA encryption of passwords during the client connection process:

1. Create the RSA private and public key-pair files using the instructions in Section 6.4.6, “Creating SSL and RSA Certificates and Keys”.

2. If the private and public key files are located in the data directory and are named private_key.pem and public_key.pem (the default values of the sha256_password_private_key_path and sha256_password_public_key_path system variables), the server uses them automatically at startup.

   Otherwise, in the server option file, set the system variables to the key file names. If the files are located in the server data directory, you need not specify their full path names:

   [mysqld]
   sha256_password_private_key_path=myprivkey.pem
   sha256_password_public_key_path=mypubkey.pem

   If the key files are not located in the data directory, or to make their locations explicit in the system variable values, use full path names:

   [mysqld]
   sha256_password_private_key_path=/usr/local/mysql/myprivkey.pem
   sha256_password_public_key_path=/usr/local/mysql/mypubkey.pem

3. Restart the server, then connect to it and check the Rsa_public_key status variable value. The value will differ from that shown here, but should be nonempty:

   mysql> SHOW STATUS LIKE 'Rsa_public_key'\G
   *************************** 1. row ***************************
   Variable_name: Rsa_public_key
           Value: -----BEGIN PUBLIC KEY-----
   MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDO9nRUDd+KvSZgY7cNBZMNpwX6
   MvE1PbJFXO7u18nJ9lwc99Du/E7lw6CVXw7VKrXPeHbVQUzGyUNkf45Nz/ckaaJa
   aLgJOBCIDmNVnyU54OT/1lcs2xiyfaDMe8fCJ64ZwTnKbY2gkt1IMjUAB5Ogd5kJ
   g8aV7EtKwyhHb0c30QIDAQAB
   -----END PUBLIC KEY-----

   If the value is empty, the server found some problem with the key files. Check the error log for diagnostic information.

After the server has been configured with the RSA key files, accounts that authenticate with the sha256_password plugin have the option of using those key files to connect to the server. As mentioned previously, such accounts can use either an SSL connection (in which case RSA is not used) or an unencrypted connection that encrypts the password using RSA. Assume for the following discussion that SSL is not used. Connecting to the server involves no special preparation on the client side. For example:

shell> mysql --ssl-mode=DISABLED -u sha256user -p
Enter password: Sh@256Pa33

For connection attempts by sha256user, the server determines that sha256_password is the appropriate authentication plugin and invokes it. The plugin finds that the connection does not use SSL and thus requires the password to be transmitted using RSA encryption. In this case, the plugin sends the RSA public key to the client, which uses it to encrypt the password and returns the result to the server. The plugin uses the RSA key on the server side to decrypt the password and accepts or rejects the connection based on whether the password is correct.

The server sends the public key to the client as needed, but if a copy of the RSA public key is available on the client host, the client can use it to save a round trip in the client/server protocol:

shell> mysql --ssl-mode=DISABLED -u sha256user -p --server-public-key-path=file_name
Enter password: Sh@256Pa33

The public key value in the file named by the --server-public-key-path option should be the same as the key value in the server-side file named by the sha256_password_public_key_path system variable. If the key file contains a valid public key value but the value is incorrect, an access-denied error occurs. If the key file does not contain a valid public key, the client program cannot use it. In this case, the sha256_password plugin sends the public key to the client as if no --server-public-key-path option had been specified.

Client users can get the RSA public key two ways:

• The database administrator can provide a copy of the public key file.

• A client user who can connect to the server some other way can use a SHOW STATUS LIKE 'Rsa_public_key' statement and save the returned key value in a file.