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><H1
CLASS="SECT1"
><A
NAME="SSL-TCP"
>17.9. Secure TCP/IP Connections with SSL</A
></H1
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> has native support for using
<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connections to encrypt client/server communications
for increased security. This requires that
<SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> is installed on both client and
server systems and that support in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is
enabled at build time (see <A
HREF="installation.html"
>Chapter 15</A
>).
</P
><P
> With <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> support compiled in, the
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server can be started with
<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> enabled by setting the parameter
<A
HREF="runtime-config-connection.html#GUC-SSL"
>ssl</A
> to <TT
CLASS="LITERAL"
>on</TT
> in
<TT
CLASS="FILENAME"
>postgresql.conf</TT
>. The server will listen for both normal
and <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connections on the same TCP port, and will negotiate
with any connecting client on whether to use <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
>. By
default, this is at the client's option; see <A
HREF="auth-pg-hba-conf.html"
>Section 19.1</A
> about how to set up the server to require
use of <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> for some or all connections.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> reads the system-wide
<SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> configuration file. By default, this
file is named <TT
CLASS="FILENAME"
>openssl.cnf</TT
> and is located in the
directory reported by <TT
CLASS="LITERAL"
>openssl version -d</TT
>.
This default can be overridden by setting environment variable
<TT
CLASS="ENVAR"
>OPENSSL_CONF</TT
> to the name of the desired configuration file.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> supports a wide range of ciphers
and authentication algorithms, of varying strength. While a list of
ciphers can be specified in the <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
>
configuration file, you can specify ciphers specifically for use by
the database server by modifying <A
HREF="runtime-config-connection.html#GUC-SSL-CIPHERS"
>ssl_ciphers</A
> in
<TT
CLASS="FILENAME"
>postgresql.conf</TT
>.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> It is possible to have authentication without encryption overhead by
using <TT
CLASS="LITERAL"
>NULL-SHA</TT
> or <TT
CLASS="LITERAL"
>NULL-MD5</TT
> ciphers. However,
a man-in-the-middle could read and pass communications between client
and server. Also, encryption overhead is minimal compared to the
overhead of authentication. For these reasons NULL ciphers are not
recommended.
</P
></BLOCKQUOTE
></DIV
><P
> To start in <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> mode, files containing the server certificate
and private key must exist. By default, these files are expected to be
named <TT
CLASS="FILENAME"
>server.crt</TT
> and <TT
CLASS="FILENAME"
>server.key</TT
>, respectively, in
the server's data directory, but other names and locations can be specified
using the configuration parameters <A
HREF="runtime-config-connection.html#GUC-SSL-CERT-FILE"
>ssl_cert_file</A
>
and <A
HREF="runtime-config-connection.html#GUC-SSL-KEY-FILE"
>ssl_key_file</A
>.
On Unix systems, the permissions on <TT
CLASS="FILENAME"
>server.key</TT
> must
disallow any access to world or group; achieve this by the command
<TT
CLASS="COMMAND"
>chmod 0600 server.key</TT
>.
If the private key is protected with a passphrase, the
server will prompt for the passphrase and will not start until it has
been entered.
</P
><P
> In some cases, the server certificate might be signed by an
<SPAN
CLASS="QUOTE"
>"intermediate"</SPAN
> certificate authority, rather than one that is
directly trusted by clients. To use such a certificate, append the
certificate of the signing authority to the <TT
CLASS="FILENAME"
>server.crt</TT
> file,
then its parent authority's certificate, and so on up to a <SPAN
CLASS="QUOTE"
>"root"</SPAN
>
authority that is trusted by the clients. The root certificate should
be included in every case where <TT
CLASS="FILENAME"
>server.crt</TT
> contains more than
one certificate.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SSL-CLIENT-CERTIFICATES"
>17.9.1. Using Client Certificates</A
></H2
><P
> To require the client to supply a trusted certificate, place
certificates of the certificate authorities (<ACRONYM
CLASS="ACRONYM"
>CA</ACRONYM
>s)
you trust in the file <TT
CLASS="FILENAME"
>root.crt</TT
> in the data
directory, set the parameter <A
HREF="runtime-config-connection.html#GUC-SSL-CA-FILE"
>ssl_ca_file</A
> in
<TT
CLASS="FILENAME"
>postgresql.conf</TT
> to <TT
CLASS="LITERAL"
>root.crt</TT
>,
and set the <TT
CLASS="LITERAL"
>clientcert</TT
> parameter
to 1 on the appropriate <TT
CLASS="LITERAL"
>hostssl</TT
> line(s) in
<TT
CLASS="FILENAME"
>pg_hba.conf</TT
>.
A certificate will then be requested from the client during
SSL connection startup. (See <A
HREF="libpq-ssl.html"
>Section 31.18</A
> for a
description of how to set up certificates on the client.) The server will
verify that the client's certificate is signed by one of the trusted
certificate authorities. Certificate Revocation List (CRL) entries
are also checked if the parameter <A
HREF="runtime-config-connection.html#GUC-SSL-CRL-FILE"
>ssl_crl_file</A
> is set.
(See <A
HREF="http://h71000.www7.hp.com/doc/83final/ba554_90007/ch04s02.html"
TARGET="_top"
>http://h71000.www7.hp.com/doc/83final/ba554_90007/ch04s02.html</A
>
for diagrams showing SSL certificate usage.)
</P
><P
> The <TT
CLASS="LITERAL"
>clientcert</TT
> option in <TT
CLASS="FILENAME"
>pg_hba.conf</TT
> is
available for all authentication methods, but only for rows specified as
<TT
CLASS="LITERAL"
>hostssl</TT
>. When <TT
CLASS="LITERAL"
>clientcert</TT
> is not specified
or is set to 0, the server will still verify presented client
certificates against its CA list, if one is configured,
— but it will not insist that a client certificate be presented.
</P
><P
> Note that <TT
CLASS="FILENAME"
>root.crt</TT
> lists the top-level CAs that are
considered trusted for signing client certificates. In principle it need
not list the CA that signed the server's certificate, though in most cases
that CA would also be trusted for client certificates.
</P
><P
> If you are setting up client certificates, you may wish to use
the <TT
CLASS="LITERAL"
>cert</TT
> authentication method, so that the certificates
control user authentication as well as providing connection security.
See <A
HREF="auth-methods.html#AUTH-CERT"
>Section 19.3.10</A
> for details.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SSL-SERVER-FILES"
>17.9.2. SSL Server File Usage</A
></H2
><P
> <A
HREF="ssl-tcp.html#SSL-FILE-USAGE"
>Table 17-3</A
> summarizes the files that are
relevant to the SSL setup on the server. (The shown file names are default
or typical names. The locally configured names could be different.)
</P
><DIV
CLASS="TABLE"
><A
NAME="SSL-FILE-USAGE"
></A
><P
><B
>Table 17-3. SSL Server File Usage</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>File</TH
><TH
>Contents</TH
><TH
>Effect</TH
></TR
></THEAD
><TBODY
><TR
><TD
><A
HREF="runtime-config-connection.html#GUC-SSL-CERT-FILE"
>ssl_cert_file</A
> (<TT
CLASS="FILENAME"
>$PGDATA/server.crt</TT
>)</TD
><TD
>server certificate</TD
><TD
>sent to client to indicate server's identity</TD
></TR
><TR
><TD
><A
HREF="runtime-config-connection.html#GUC-SSL-KEY-FILE"
>ssl_key_file</A
> (<TT
CLASS="FILENAME"
>$PGDATA/server.key</TT
>)</TD
><TD
>server private key</TD
><TD
>proves server certificate was sent by the owner; does not indicate
certificate owner is trustworthy</TD
></TR
><TR
><TD
><A
HREF="runtime-config-connection.html#GUC-SSL-CA-FILE"
>ssl_ca_file</A
> (<TT
CLASS="FILENAME"
>$PGDATA/root.crt</TT
>)</TD
><TD
>trusted certificate authorities</TD
><TD
>checks that client certificate is
signed by a trusted certificate authority</TD
></TR
><TR
><TD
><A
HREF="runtime-config-connection.html#GUC-SSL-CRL-FILE"
>ssl_crl_file</A
> (<TT
CLASS="FILENAME"
>$PGDATA/root.crl</TT
>)</TD
><TD
>certificates revoked by certificate authorities</TD
><TD
>client certificate must not be on this list</TD
></TR
></TBODY
></TABLE
></DIV
><P
> The files <TT
CLASS="FILENAME"
>server.key</TT
>, <TT
CLASS="FILENAME"
>server.crt</TT
>,
<TT
CLASS="FILENAME"
>root.crt</TT
>, and <TT
CLASS="FILENAME"
>root.crl</TT
>
(or their configured alternative names)
are only examined during server start; so you must restart
the server for changes in them to take effect.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SSL-CERTIFICATE-CREATION"
>17.9.3. Creating a Self-signed Certificate</A
></H2
><P
> To create a quick self-signed certificate for the server, use the
following <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> command:
</P><PRE
CLASS="PROGRAMLISTING"
>openssl req -new -text -out server.req</PRE
><P>
Fill out the information that <SPAN
CLASS="APPLICATION"
>openssl</SPAN
> asks for. Make sure
you enter the local host name as <SPAN
CLASS="QUOTE"
>"Common Name"</SPAN
>; the challenge
password can be left blank. The program will generate a key that is
passphrase protected; it will not accept a passphrase that is less
than four characters long. To remove the passphrase (as you must if
you want automatic start-up of the server), run the commands:
</P><PRE
CLASS="PROGRAMLISTING"
>openssl rsa -in privkey.pem -out server.key
rm privkey.pem</PRE
><P>
Enter the old passphrase to unlock the existing key. Now do:
</P><PRE
CLASS="PROGRAMLISTING"
>openssl req -x509 -in server.req -text -key server.key -out server.crt</PRE
><P>
to turn the certificate into a self-signed certificate and to copy
the key and certificate to where the server will look for them.
Finally do:
</P><PRE
CLASS="PROGRAMLISTING"
>chmod og-rwx server.key</PRE
><P>
because the server will reject the file if its permissions are more
liberal than this.
For more details on how to create your server private key and
certificate, refer to the <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> documentation.
</P
><P
> A self-signed certificate can be used for testing, but a certificate
signed by a certificate authority (<ACRONYM
CLASS="ACRONYM"
>CA</ACRONYM
>) (either one of the
global <ACRONYM
CLASS="ACRONYM"
>CAs</ACRONYM
> or a local one) should be used in production
so that clients can verify the server's identity. If all the clients
are local to the organization, using a local <ACRONYM
CLASS="ACRONYM"
>CA</ACRONYM
> is
recommended.
</P
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