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Host Certificates


This document describes how to get host certificates.

Host certificates are X.509 certificates that are used to securely identify servers and to establish encrypted connections between services and clients. In the OSG Fabric of Services, some services (e.g., HTCondor-CE, XRootD) require host certificates. If you are unsure if your host needs a host certificate, please consult the installation instructions for the software you are interested in installing.

Before Starting

Before requesting a new host certificate, use openssl to check if your host already has a valid certificate, i.e. the present is between notBefore and notAfter dates and times. If so, you may safely skip this document:

user@host $ openssl x509 -in /etc/grid-security/hostcert.pem -subject -issuer -dates -noout
subject= /DC=org/DC=opensciencegrid/O=Open Science Grid/OU=Services/
issuer=/DC=org/DC=cilogon/C=US/O=CILogon/CN=CILogon OSG CA 1
notBefore=Jan  4 21:08:09 2010 GMT
notAfter=Jan  4 21:08:09 2011 GMT

If you are using OpenSSL 1.1, you may notice minor formatting differences.

Requesting Host Certificates

To acquire a host certificate, you must submit a request to a Certificate Authority (CA). We recommend requesting host certificates from one of the following CAs:

  • InCommon IGTF: an IGTF-accredited CA for services that interact with the WLCG; requires a subscription, generally held by an institution


    For integration with the OSG Fabric of Services, InCommon host certificates must be issued by the IGTF CA and not the InCommon RSA CA.

  • Let's Encrypt: a free, automated, and open CA frequently used for web services; see the security team's position on Let's Encrypt for more details. Let's Encrypt is not IGTF-accredited so their certificates are not suitable for WLCG services.

If neither of the above options work for your site, the OSG Fabric of Services also accepts all IGTF-accredited CAs.


For SSL to work properly, you will need to request a host certificate with "TLS Web Server Authentication" and "TLS Web Client Authentication" included in the X509v3 Extended Key Usage.

Requesting Service Certificates

Previously, the OSG Consortium recommended using separate X.509 certificates, called "service certificates", for each service on a host. This practice has become less popular as sites have separated SSL-requiring services to their own hosts.

In the case where your host is only running a single service that requires a service certificate, we recommend using your host certificate as your service certificate. Ensure that the ownership of the host certificate and key are appropriate for the service you are running.

If you are running multiple services that require host certificates, we recommend requesting a certificate whose CommonName is <service>-hostname and has the hostname in the list of subject alternative names.

Frequently Asked Questions

Can I use any host to request a certificate for a different host?

YES, you can use any host to create a certificate signing request as long as the hostname for the certificate is a fully qualified domain name.

How do I renew a host certificate?

For Let's Encrypt certificates, see this section

For other certificates, there is no separate renewal procedure. Instead, request a new certificate using one of the methods above.

How can I check if I have a host certificate installed already?

By default the host certificate key pair will be installed in /etc/grid-security/hostcert.pem and /etc/grid-security/hostkey.pem. You can use openssl to access basic information about the certificate:

root@host # openssl x509 -in /etc/grid-security/hostcert.pem -subject -issuer -dates -noout
subject= /DC=org/DC=opensciencegrid/O=Open Science Grid/OU=Services/
issuer= /DC=org/DC=cilogon/C=US/O=CILogon/CN=CILogon OSG CA 1
notBefore=Apr  8 00:00:00 2013 GMT
notAfter=May 17 12:00:00 2014 GMT


The openssl version 1.1.x command prints the subject DN in a slightly different format. OpenSSL version 1.1 is present on Enterprise Linux 8 systems. The new format is a comma separated list of attributes. You must convert that back to the older format for our map files. Each attribute must start with a / and there are no spaces around the = and remove the comma between attributes:

DC = org, DC = opensciencegrid, O = Open Science Grid, OU = People, CN = Matyas Selmeci

should be written as:

/DC=org/DC=opensciencegrid/O=Open Science Grid/OU=People/CN=Matyas Selmeci

How can I check the expiration time of my installed host certificate?

Use the following openssl command to find the dates that your host certificate is valid:

root@host # openssl x509 -in /etc/grid-security/hostcert.pem -dates -noout
notBefore=Jan  4 21:08:41 2010 GMT
notAfter=Jan  4 21:08:41 2011 GMT


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