password from the client.
  </para>

  <para>
    To prevent spoofing with GSSAPI, the server must be configured to accept
    only <literal>hostgssenc</literal> connections
    (<xref linkend="auth-pg-hba-conf"/>) and use <literal>gss</literal>
    authentication with them.  The TCP client must connect
    using <literal>gssencmode=require</literal>.
  </para>
 </sect1>

 <sect1 id="encryption-options">
  <title>Encryption Options</title>

  <indexterm zone="encryption-options">
   <primary>encryption</primary>
  </indexterm>

  <para>
   <productname>PostgreSQL</productname> offers encryption at several
   levels, and provides flexibility in protecting data from disclosure
   due to database server theft, unscrupulous administrators, and
   insecure networks. Encryption might also be required to secure
   sensitive data such as medical records or financial transactions.
  </para>

  <variablelist>

  <varlistentry>
   <term>Password Encryption</term>
   <listitem>

    <para>
     Database user passwords are stored as hashes (determined by the setting
     <xref linkend="guc-password-encryption"/>), so the administrator cannot
     determine the actual password assigned to the user. If SCRAM or MD5
     encryption is used for client authentication, the unencrypted password is
     never even temporarily present on the server because the client encrypts
     it before being sent across the network. SCRAM is preferred, because it
     is an Internet standard and is more secure than the PostgreSQL-specific
     MD5 authentication protocol.
    </para>

    <warning>
     <para>
      Support for MD5-encrypted passwords is deprecated and will be removed in
      a future release of <productname>PostgreSQL</productname>.  Refer to
      <xref linkend="auth-password"/> for details about migrating to another
      password type.
     </para>
    </warning>

   </listitem>
  </varlistentry>

  <varlistentry>
   <term>Encryption For Specific Columns</term>

   <listitem>
    <para>
     The <xref linkend="pgcrypto"/> module allows certain fields to be
     stored encrypted.
     This is useful if only some of the data is sensitive.
     The client supplies the decryption key and the data is decrypted
     on the server and then sent to the client.
    </para>

    <para>
     The decrypted data and the decryption key are present on the
     server for a brief time while it is being decrypted and
     communicated between the client and server. This presents a brief
     moment where the data and keys can be intercepted by someone with
     complete access to the database server, such as the system
     administrator.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term>Data Partition Encryption</term>

   <listitem>
    <para>
     Storage encryption can be performed at the file system level or the
     block level.  Linux file system encryption options include eCryptfs
     and EncFS, while FreeBSD uses PEFS.  Block level or full disk
     encryption options include dm-crypt + LUKS on Linux and GEOM
     modules geli and gbde on FreeBSD.  Many other operating systems
     support this functionality, including Windows.
    </para>

    <para>
     This mechanism prevents unencrypted data from being read from the
     drives if the drives or the entire computer is stolen. This does
     not protect against attacks while the file system is mounted,
     because when mounted, the operating system provides an unencrypted
     view of the data. However, to mount the file system, you need some
     way for the encryption key to be passed to the operating system,
     and sometimes the key is stored somewhere on the host that mounts
     the disk.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term>Encrypting Data Across A Network</term>

    <listitem>
     <para>
      SSL connections encrypt all data sent across the network: the
      password, the queries, and the data returned. The
      <filename>pg_hba.conf</filename>