<indexterm>
<primary>MD5</>
</indexterm>
+ <indexterm>
+ <primary>SCRAM</>
+ </indexterm>
<indexterm>
<primary>password</primary>
<secondary>authentication</secondary>
</indexterm>
<para>
- The password-based authentication methods are <literal>scram-sha-256</>,
- <literal>md5</>, and <literal>password</>. These methods operate
- similarly except for the way that the password is sent across the
+ There are several password-based authentication methods. These methods
+ operate similarly but differ in how the users' passwords are stored on the
+ server and how the password provided by a client is sent across the
connection.
</para>
- <para>
- Plain <literal>password</> sends the password in clear-text, and is
- therefore vulnerable to password <quote>sniffing</> attacks. It should
- always be avoided if possible. If the connection is protected by SSL
- encryption then <literal>password</> can be used safely, though.
- (Though SSL certificate authentication might be a better choice if one
- is depending on using SSL).
- </para>
+ <variablelist>
+ <varlistentry>
+ <term><literal>scram-sha-256</literal></term>
+ <listitem>
+ <para>
+ The method <literal>scram-sha-256</> performs SCRAM-SHA-256
+ authentication, as described in
+ <ulink url="https://tools.ietf.org/html/rfc7677">RFC 7677</ulink>. It
+ is a challenge-response scheme that prevents password sniffing on
+ untrusted connections and supports storing passwords on the server in a
+ cryptographically hashed form that is thought to be secure.
+ </para>
+ <para>
+ This is the most secure of the currently provided methods, but it is
+ not supported by older client libraries.
+ </para>
+ </listitem>
+ </varlistentry>
- <para>
- <literal>scram-sha-256</> performs SCRAM-SHA-256 authentication, as
- described in
- <ulink url="https://tools.ietf.org/html/rfc7677">RFC 7677</ulink>. It
- is a challenge-response scheme, that prevents password sniffing on
- untrusted connections. It is more secure than the <literal>md5</>
- method, but might not be supported by older clients.
- </para>
+ <varlistentry>
+ <term><literal>md5</literal></term>
+ <listitem>
+ <para>
+ The method <literal>md5</> uses a custom less secure challenge-response
+ mechanism. It prevents password sniffing and avoids storing passwords
+ on the server in plain text but provides no protection if an attacker
+ manages to steal the password hash from the server. Also, the MD5 hash
+ algorithm is nowadays no longer consider secure against determined
+ attacks.
+ </para>
- <para>
- <literal>md5</> allows falling back to a less secure challenge-response
- mechanism for those users with an MD5 hashed password.
- The fallback mechanism also prevents password sniffing, but provides no
- protection if an attacker manages to steal the password hash from the
- server, and it cannot be used with the <xref
- linkend="guc-db-user-namespace"> feature. For all other users,
- <literal>md5</> works the same as <literal>scram-sha-256</>.
- </para>
+ <para>
+ The <literal>md5</literal> method cannot be used with
+ the <xref linkend="guc-db-user-namespace"> feature.
+ </para>
+
+ <para>
+ To ease transition from the <literal>md5</literal> method to the newer
+ SCRAM method, if <literal>md5</literal> is specified as a method
+ in <filename>pg_hba.conf</filename> but the user's password on the
+ server is encrypted for SCRAM (see below), then SCRAM-based
+ authentication will automatically be chosen instead.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>password</literal></term>
+ <listitem>
+ <para>
+ The method <literal>password</> sends the password in clear-text and is
+ therefore vulnerable to password <quote>sniffing</> attacks. It should
+ always be avoided if possible. If the connection is protected by SSL
+ encryption then <literal>password</> can be used safely, though.
+ (Though SSL certificate authentication might be a better choice if one
+ is depending on using SSL).
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
<para>
<productname>PostgreSQL</productname> database passwords are
catalog. Passwords can be managed with the SQL commands
<xref linkend="sql-createuser"> and
<xref linkend="sql-alterrole">,
- e.g., <userinput>CREATE USER foo WITH PASSWORD 'secret'</userinput>.
+ e.g., <userinput>CREATE USER foo WITH PASSWORD 'secret'</userinput>,
+ or the <application>psql</application>
+ command <literal>\password</literal>.
If no password has been set up for a user, the stored password
is null and password authentication will always fail for that user.
</para>
+ <para>
+ The availability of the different password-based authentication methods
+ depends on how a user's password on the server is encrypted (or hashed,
+ more accurately). This is controlled by the configuration
+ parameter <xref linkend="guc-password-encryption"> at the time the
+ password is set. If a password was encrypted using
+ the <literal>scram-sha-256</literal> setting, then it can be used for the
+ authentication methods <literal>scram-sha-256</literal>
+ and <literal>password</literal> (but password transmission will be in
+ plain text in the latter case). The authentication method
+ specification <literal>md5</literal> will automatically switch to using
+ the <literal>scram-sha-256</literal> method in this case, as explained
+ above, so it will also work. If a password was encrypted using
+ the <literal>md5</literal> setting, then it can be used only for
+ the <literal>md5</literal> and <literal>password</literal> authentication
+ method specifications (again, with the password transmitted in plain text
+ in the latter case). (Previous PostgreSQL releases supported storing the
+ password on the server in plain text. This is no longer possible.) To
+ check the currently stored password hashes, see the system
+ catalog <literal>pg_authid</literal>.
+ </para>
+
+ <para>
+ To upgrade an existing installation from <literal>md5</literal>
+ to <literal>scram-sha-256</literal>, after having ensured that all client
+ libraries in use are new enough to support SCRAM,
+ set <literal>password_encryption = 'scram-sha-256'</literal>
+ in <filename>postgresql.conf</filename>, make all users set new passwords,
+ and change the authentication method specifications
+ in <filename>pg_hba.conf</filename> to <literal>scram-sha-256</literal>.
+ </para>
</sect2>
<sect2 id="gssapi-auth">
projects / postgresql / commitdiff