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Tech Document Sep 26, 2018

How to Generate Certificate Signing Request on FreeIPA

This article will go into detail on how to generate certificate signing request on FreeIPA.

Introduction

Status

Feature complete, needs testing.

Fedora

The dogtag packages are now available in Fedora. The required packages should be pulled in as dependencies when ipa-server is installed.

This just makes the binaries available for the IPA installer script. The installer creates and configures the necessary dogtag components to stand up a CA.

Installing

A dogtag CA is installed by default by IPA. To install using a self-signed CA instead of dogtag pass in the --selfsignargument to ipa-server-install.

The CA uses a separate instance of DS that is used only for the CA. This instance is named PKI-IPA.

It will install a CA instance into /var/lib/pki-ca.

A copy of the root CA certificate and private key will be put into /root/cacert.p12.

A copy of the CA agent certificate will be put into /root/ca-agent.p12. This agent certificate can be imported into a browser and used to administer CS using the web interface (not recommended).

Use a Different CA to sign the IPA CA certificate

If you have an existing CA you can use it make the IPA CA a subordinate.

This is a three-step process:

  • Have ipa-server-install generate a Certificate Signing Request (CSR)
  • Take the CSR to your CA and have it signed
  • Provide the resulting certificate to ipa-server-install to complete the installation

Detailed instructions

Run ipa-server-install with whatever arguments are appropriate for your environment and include the --external_ca flag:

<pre># ipa-server-install --external-ca </pre>

This will generate a CSR in /root/ipa.csr. This is the file you need to provide to your CA for signing. You will also need to obtain a PEM copy of your CA trust chain.

Once you have both of these you can continue the installer:

<pre># ipa-server-install --external_cert_file=/root/ipa.crt --external_ca_file=/root/existing_ca.crt </pre>

The server caches the answers the first time you run the installer so you don't need to answer the questions again the second time. This cache is removed when the installer is run again.

The paths to the certificate and CA must be absolute paths. The dogtag silent installer will fail if they are not.

Once the installation is complete you will have the same files as a standalone IPA CA: /root/cacert.p12 and /root/ca-agent.p12.

The only difference is that the CA certificate is signed by your external CA in this mode and self-signed in the default mode.

Using Certificates From a Different CA

If don't you want to use the new IPA CA features at all that is ok but you'll need to take a few extra steps.

There are two ways to achieve this:

  • Install IPA using the selfsign CA and replace the server certs post-installation
  • Provide PKCS#12 files to the installer (and still use the selfsign CA, it just won't generate any certs)

The step setting enable_ra to False disables the cert plugin in the XML-RPC interface. Your IPA server will be unable to issue certificates.

Install and Replace

To use the Install and Replace method do the following:

  • Install IPA server with the --selfsign option
  • Once IPA is up and working run ipa-server-certinstall once for the DS and once for Apache to replace the server certificates
  • If you want the Firefox autoconfiguration to work use an object signing certificate to sign the jar file in /usr/share/ipa/html/configure.jar
  • Replace the CA certificate in /etc/ipa/ca.crt and /usr/share/ipa/html/ca.crt
  • Edit /etc/ipa/default.conf and set enable_ra to False
  • Restart Apache

Install with your own certificates

To use the Install your own method do the following:

  • Install IPA server with the --http_pkcs12 and --dirsrv_pkcs12 and their respective pin arguments. Your PKCS#12 files should contain the server cert, key and the CA cert chain.
  • If you want the Firefox autoconfiguration to work use an object signing certificate to sign the jar file in /usr/share/ipa/html/configure.jar
  • Verify that the CA certificate in /etc/ipa/ca.crt and /usr/share/ipa/html/ca.crt are correct
  • Edit /etc/ipa/default.conf and set enable_ra to False
  • Restart Apache

Working with Certificates

Once your CA is configured authorized users can perform a number of operations.

Request a certificate

You start with a Certificate Signing Request (CSR). In our case this is a base-64 encoded PKCS#10 request which looks something like:

<pre>-----BEGIN CERTIFICATE REQUEST----- MIIBnTCCAQYCAQAwXTELMAkGA1UEBhMCU0cxETAPBgNVBAoTCE0yQ3J5cHRvMRIw EAYDVQQDEwlsb2NhbGhvc3QxJzAlBgkqhkiG9w0BCQEWGGFkbWluQHNlcnZlci5l ... ... 9rsQkRc9Urv9mRBIsredGnYECNeRaK5R1yzpOowninXC -----END CERTIFICATE REQUEST----- </pre>

To generate a CSR using OpenSSL run:

<pre>% openssl req -new -nodes -out host.csr </pre>

You will be prompted for the contents of the certificate subject (country, state, organization, etc). The only critical piece is the common name, this needs to be set to the FQDN of your host.

The CSR is in the file host.csr and the key for this request is in privkey.pem

In NSS you need to start with a cert database so you have an extra step. An NSS CSR generation looks like:

% certutil -N -d /tmp/test % certutil -R -s "CN=ipa.example.com" -d /tmp/test -o test.csr -g 2048 -a

The CSR needs to be passed as one single string on the command-line:

$ ipa cert-request --principal=ldap2/zeus.example.com --add 'MIIBejCB5AIBADA7MQwwCgYDVQQKEwNJUEExEDAOBgNVBAsTB3BraS1pcGExGTAXBgNVBAMTEHpldXMuZ3JleW9hay5jb20wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBANSiseMKVF/ft44rJDM5XKaMo6jo03TBAC2i61D1GZL6nZ1trl6Oc4YfXccrbQLQ4RGLB6vwDE8vHyYh36OICb1EiWJ+bRaPsn9FaO2mk4qyZp2U/om52BCTSrOq+O+EhTdqLs+hUmUFRDpzmGX3x3UU0JR7cPcvNbcnNQvqfb2NAgMBAAGgADANBgkq > hkiG9w0BAQUFAAOBgQAjWFSgv3KZbcjn8V3rhAnuXG9xFzsqD5XsDRBsIMIrG/KNtw4VZBzuXlU2zOdoYm1vlSlzwep9xWXJi5L8HejyqPiCf2mLB60ZxBJLbe1UQ07+oCBMrxck4VXmnySWekRzfYy9lqV0lP/3A5UC6jbtrqJ6t5mp3yiwkjEzEJGp3A=='

certificate: 

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 request_id: 11 serial_number: 0xb status: 0 subject: CN=zeus.example.com,OU=pki-ipa,O=IPA

There is also a short-cut method though it isn't working today (Oct 9).

ipa cert-request file://test.csr --principal=ldap3/zeus.example.com --add

Put a cert on hold

$ ipa cert-revoke --revocation-reason=6 0xb

Remove a cert from hold

$ ipa cert-revoke --revocation-reason=6 0xb

Revoke a certificate

$ ipa cert-revoke --revocation-reason=1 0xb revoked: True status: 0

Retrieve a revoked certificate

$ ipa cert-get 0xb certificate: MIIC7D... revocation_reason: 1 status: 0

Revocation

When you want a certificate to go away you revoke it. RFC 5280 defines the following reasons for revocation:

  • 0 - unspecified
  • 1 - keyCompromise
  • 2 - cACompromise
  • 3 - affiliationChanged
  • 4 - superseded
  • 5 - cessationOfOperation
  • 6 - certificateHold
  • 8 - removeFromCRL
  • 9 - privilegeWithdrawn
  • 10 - aACompromise

Note that reason code 7 is not used.

A CRL is generated by the CA that contains a list of revoked certificates. This may be retrieved from an IPA server at: http://ipa.example.com/ipa/crl... with Services

Note this services capability is not in alpha 1

When requesting a certificate a number of things happen:

  • The server checks the virtual ACI "request certificate" to see if the requestor has permission to request certificates.
  • The subject of the certificate is compared to the hostname in the requested principal. They must match.
  • The requested service record is retrieved. If the service already has a userCertificate attribute then the request stops
  • If the service does not exist and the --add argument wasn't provided then the request stops
  • If the --add option was requested and the requestor doesn't have permission to add services the request stops
  • The requestor must be listed in the managedBy attribute of the service record.

managedBy attribute

This is a multi-value attribute that contains the distinguished name of all hosts that are allowed to write the userCertificate attribute of this service. Use the service-add-host and service-remove-host to control access.

Example

This example demonstrates the steps need to be taken by an administrator and a client machine that is attempting to request a certificate for itself. This assumes that the CSR has already been generated and is in the file web.csr in the current directory.

admin

ipa host-add client.example.com --password=secret123 ipa service-add HTTP/client.example.com ipa service-add-host --hosts=client.example.com HTTP/client.example.com ipa rolegroup-add-member --hosts=client.example.com certadmin

client

ipa-client-install ipa-join -w secret123 kinit -kt /etc/krb5.keytab host/client.example.com ipa -d cert-request file://web.csr --principal=HTTP/client.example.com

What this does

admin

  • Add a new host with a one-time password
  • Create an HTTP service principal for the host
  • Allow the host to manage its own userCertificate attribute
  • Allow the host to manage certificates (request, revoke, etc)

client

  • Configure the client to use the IPA realm
  • join the host to the realm and retrieve a keytab
  • get a kerberos ticket for the machine
  • request a certificate

VPN Example

Lets consider the case of a VPN server. On an IPA client we want to set up a VPN tunnel to a remote host, perhaps at another company. To do this we need to create an entry for that remote host, a service principal to store the certificate, then we can issue the cert.

Some of this work needs to be done as an admin:

% kinit admin % ipa host-add vpn.remote.com % ipa service-add vpn/vpn.remote.com % ipa service-add-host --hosts=ipa.example.com vpn/vpn.remote.com

We've created the remote host and a service principal for it, then gave permission for the host ipa.example.com to request a certificate on behalf of vpn.remote.com. This assumes that the certificate request for vpn.remote.com is in the file vpn.csr.

On ipa.example com:

% kinit -kt /etc/krb5.keytab host/[email protected] % ipa cert-request --principal=vpn/vpn.remote.com vpn.csr % ipa service-show vpn/vpn.remote.com