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Single_OCSP_and_CRL_in_certs

Single_OCSP_and_CRL_in_certs#

__NOTOC__

Overview#

Relevant upstream tickets: #3547, #3552

Certificates issued by FreeIPA server 3.1 and later contains 2 CRL/OCSP URIs server by Dogtag CA configured by FreeIPA:

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 17 (0x11)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: O=EXAMPLE.COM, CN=Certificate Authority
        Validity
            Not Before: Apr  8 10:16:15 2013 GMT
            Not After : Apr  9 10:16:15 2015 GMT
        Subject: O=EXAMPLE.COM, CN=testcert.example.com
        ...
        X509v3 extensions:
            X509v3 Authority Key Identifier:
                keyid:9F:25:93:2F:20:2A:79:9A:A8:88:CF:CC:EB:D0:F5:43:E7:3B:B1:EE

            Authority Information Access:
                OCSP - URI:https://ipa-ca.example.com/ca/ocsp
                OCSP - URI:https://server1.example.com/ca/ocsp

            X509v3 Key Usage: critical
                Digital Signature, Non Repudiation, Key Encipherment, Data
Encipherment
            X509v3 Extended Key Usage:
                TLS Web Server Authentication, TLS Web Client Authentication
            X509v3 CRL Distribution Points:

                Full Name:
                  URI:https://ipa-ca.example.com/ipa/crl/MasterCRL.bin
                CRL Issuer:
                  DirName: O = ipaca, CN = Certificate Authority

                Full Name:
                  URI:https://server1.example.com/ipa/crl/MasterCRL.bin
                CRL Issuer:
                  DirName: O = ipaca, CN = Certificate Authority
                  ...

One OCSP/CRL URI points to the original CA issuing the certificate and one points to a general URL (managed by FreeIPA) pointing to any other FreeIPA CA via CNAME/A DNS record that can serve the OCSP/CRL URI in case if the original FreeIPA CA was decommissioned or unavailable at the moment.

However, it was discovered there are 2 issues related to this change:

  1. Having https in the URIs requires client (e.g. a web browser) validating the request to validate the machine serving the CRL/OCSP response itself even though he CRL/OCSP response is already signed by the CA and thus verifiable. Clients will fail to retrieve the CRL/OCSP in case of the general address as it is just a CNAME for a FreeIPA server whose certificate does not allow it to serve this address.

  2. Even though we have 2 OCSP URIs in the certificate, the Firefox browser will not fail over to the general URI due to limitation in NSS which only tries the last OCSP and then fail when it is not available.

Use Cases#

  • Client browser with strict OCSP check tries to validate certificate issued by FreeIPA for a web service. When OCSP URIs are not right (due to limitations above), client browser may refuse to open the page

  • Any other client software may try to validate a certificate issues by FreeIPA

Design#

Issue certificates with just one OCSP/CRL URI pointing to the general DNS name ipa-ca.$DOMAIN. This DNS name will contain A/AAAA DNS records to all FreeIPA CAs and it will be automatically maintained by FreeIPA (if it manages DNS). Otherwise, administrator would need to maintain this DNS name on his own if he wants to keep the OCSP/CRL links functional.

The general name ipa-ca.$DOMAIN was originally implemented to contain a list of CNAMEs pointing to FreeIPA masters with CA installed. This DNS record needs to be changed to use A/AAAA records instead as DNS specification forbids multiple CNAMEs in one DNS name.

Implementation#

  • ipa-replica-install and ipa-ca-install needs to be updated to add A/AAAA records to ipa-ca.$DOMAIN when replica with CA is being installed

  • ipa-csreplica-manage del command should delete A/AAAA record from ipa-ca.$DOMAIN of the deleted CA replica

  • When IPA server is being upgraded, it should convert existing ipa-ca.$DOMAIN based on CNAMEs to version based on A/AAAA addresses. When there was a custom update to ipa-ca.$DOMAIN, upgrade should not touch it.

Feature Management#

UI

No change to UI needed. The change is done under-the-hood and in the installation tools.

CLI

No change to CLI needed.

Major configuration options and enablement#

The feature is enabled by default.

Replication#

Certificates are already replicated, so no change in this area.

Updates and Upgrades#

When FreeIPA is upgraded to the new version, it should:

  1. Update ipa-ca.$DOMAIN DNS name to use A/AAAA instead of CNAMEs

  2. Update FreeIPA Dogtag certificate profile to use single OCSP/CRL URI for new certificates. When already issued certificates needs to be fixed, a new certificate needs to be issued. certmonger can be used to simplify this task on a client if it tracks the certificate:

    1. ipa-getcert list - to identify tracking request ID of a certificate that needs to be re-issued

    2. ipa-getcert resubmit -i $TRACKING_REQUEST_ID - to ask for reissue of the certificate

    3. ipa-getcert list -i $TRACKING_REQUEST_ID - to check that certificate was successfully renewed

Dependencies#

Certificate validation depends on capabilities of certificate libraries (e.g. NSS, OpenSSL). This design was based on abilities of NSS library used in Mozilla Firefox (see NSS Bug 797815 for relevant discussion).

External Impact#

Change impacts projects processing certificate issued by FreeIPA server.

RFE Author#

Martin Kosek

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