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17.9.1. Using Client Certificates

17.9.2. SSL Server File Usage

17.9.3. Creating Certificates

Note

It is possible to have authentication without encryption overhead by usingNULL-SHA orNULL-MD5 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.

To require the client to supply a trusted certificate, place certificates of the root certificate authorities (CAs) you trust in a file in the data directory, set the parameterssl_ca_file inpostgresql.conf to the new file name, and add the authentication optionclientcert=1 to the appropriatehostssl line(s) inpg_hba.conf. A certificate will then be requested from the client during SSL connection startup. (SeeSection 31.18 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.

Intermediate certificates that chain up to existing root certificates can also appear in the fileroot.crt if you wish to avoid storing them on clients (assuming the root and intermediate certificates were created withv3_ca extensions). Certificate Revocation List (CRL) entries are also checked if the parameterssl_crl_file is set. (Seehttp://h41379.www4.hpe.com/doc/83final/ba554_90007/ch04s02.html for diagrams showing SSL certificate usage.)

Theclientcert option inpg_hba.conf is available for all authentication methods, but only for rows specified ashostssl. Whenclientcert 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.

If you are setting up client certificates, you may wish to use thecert authentication method, so that the certificates control user authentication as well as providing connection security. SeeSection 19.3.9 for details.

Table 17.2 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.)

The filesserver.key,server.crt,root.crt, androot.crl (or their configured alternative names) are only examined during server start; so you must restart the server for changes in them to take effect.

To create a simple self-signed certificate for the server, valid for 365 days, use the followingOpenSSL command, replacingdbhost.yourdomain.com with the server's host name:

openssl req -new -x509 -days 365 -nodes -text -out server.crt \  -keyout server.key -subj "/CN=dbhost.yourdomain.com"

Then do:

chmod og-rwx server.key

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 theOpenSSL documentation.

While a self-signed certificate can be used for testing, a certificate signed by a certificate authority (CA) (usually an enterprise-wide rootCA) should be used in production.

To create a server certificate whose identity can be validated by clients, first create a certificate signing request (CSR) and a public/private key file:

openssl req -new -nodes -text -out root.csr \  -keyout root.key -subj "/CN=root.yourdomain.com"chmod og-rwx root.key

Then, sign the request with the key to create a root certificate authority (using the defaultOpenSSL configuration file location onLinux):

openssl x509 -req -in root.csr -text -days 3650 \  -extfile /etc/ssl/openssl.cnf -extensions v3_ca \  -signkey root.key -out root.crt

Finally, create a server certificate signed by the new root certificate authority:

openssl req -new -nodes -text -out server.csr \  -keyout server.key -subj "/CN=dbhost.yourdomain.com"chmod og-rwx server.keyopenssl x509 -req -in server.csr -text -days 365 \  -CA root.crt -CAkey root.key -CAcreateserial \  -out server.crt

server.crt andserver.key should be stored on the server, androot.crt should be stored on the client so the client can verify that the server's leaf certificate was signed by its trusted root certificate.root.key should be stored offline for use in creating future certificates.

It is also possible to create a chain of trust that includes intermediate certificates:

# rootopenssl req -new -nodes -text -out root.csr \  -keyout root.key -subj "/CN=root.yourdomain.com"chmod og-rwx root.keyopenssl x509 -req -in root.csr -text -days 3650 \  -extfile /etc/ssl/openssl.cnf -extensions v3_ca \  -signkey root.key -out root.crt# intermediateopenssl req -new -nodes -text -out intermediate.csr \  -keyout intermediate.key -subj "/CN=intermediate.yourdomain.com"chmod og-rwx intermediate.keyopenssl x509 -req -in intermediate.csr -text -days 1825 \  -extfile /etc/ssl/openssl.cnf -extensions v3_ca \  -CA root.crt -CAkey root.key -CAcreateserial \  -out intermediate.crt# leafopenssl req -new -nodes -text -out server.csr \  -keyout server.key -subj "/CN=dbhost.yourdomain.com"chmod og-rwx server.keyopenssl x509 -req -in server.csr -text -days 365 \  -CA intermediate.crt -CAkey intermediate.key -CAcreateserial \  -out server.crt

server.crt andintermediate.crt should be concatenated into a certificate file bundle and stored on the server.server.key should also be stored on the server.root.crt should be stored on the client so the client can verify that the server's leaf certificate was signed by a chain of certificates linked to its trusted root certificate.root.key andintermediate.key should be stored offline for use in creating future certificates.