Revoked certificate still valid

certificate-authorityself-signed-certificatewindows 7windows-server-2012-r2

I've recently setup a new domain joined Standalone CA on a Windows 2012 R2 server which is publicly accessible and authenticating fine, however, revoked certificates still appear to be authenticating. The actual server-side revoke process works fine as in the revoked certificate gets added to the CRL after publishing but the certificate still authenticates the client end.

I've added externally accessible CDP and AIA locations and have cleared the local CRL cache the client end using the following commands:

certutil -urlcache CRL delete

certutil -setreg chain\ChainCacheResyncFiletime @now

I'm aware of the minimum OS requirements for the last command. Clients are Windows 7 upwards.

I'm using a simple test app on the client that is configured to use the one certificate so if revoked would simply stop working but isn't the case in this instance. If I remove the certificate from local certificate stores then it does stop working so confident that it's dependant on this one certificate.

All web searches so far have led to the above commands and making sure the CDP is externally resolvable but I've covered those issues already.

I appreciate and advice

Best Answer

Thought it was worth reporting my findings.

Turns out that Windows was revoking the certificates but there was some local caching of the CRL taking place as is intended by design. It seems that even when the certificate is showing as revoked, a cached copy is still used regardless until a specific period has passed, however, from my understanding the two commands I ran in my initial post should have expired this and requested an up-to-date one from the server but doesn't appear to be the case.

I've introduced delta CRLs which have made troubleshooting must quicker and all seems fine now so false alarm ultimately.

Thanks for your advice Greg

Related Solutions

Unrevoke a certificate which was revoked with a status different from Certificate Hold

Once on the revoked list... it stays on the revoked list. That's why they recommend you NEVER revoke a cert unless you know it's been compromised.

OpenSSL – Certification Authority Root Certificate Expiry and Renewal

Keeping the same private key on your root CA allows for all certificates to continue to validate successfully against the new root; all that's required of you is to trust the new root.

The certificate signing relationship is based on a signature from the private key; keeping the same private key (and, implicitly, the same public key) while generating a new public certificate, with a new validity period and any other new attributes changed as needed, keeps the trust relationship in place. CRLs, too, can continue over from the old cert to the new, as they are, like certificates, signed by the private key.

So, let's verify!

Make a root CA:

openssl req -new -x509 -keyout root.key -out origroot.pem -days 3650 -nodes

Generate a child certificate from it:

openssl genrsa -out cert.key 1024
openssl req -new -key cert.key -out cert.csr

Sign the child cert:

openssl x509 -req -in cert.csr -CA origroot.pem -CAkey root.key -create_serial -out cert.pem
rm cert.csr

All set there, normal certificate relationship. Let's verify the trust:

# openssl verify -CAfile origroot.pem -verbose cert.pem
cert.pem: OK

Ok, so, now let's say 10 years passed. Let's generate a new public certificate from the same root private key.

openssl req -new -key root.key -out newcsr.csr
openssl x509 -req -days 3650 -in newcsr.csr -signkey root.key -out newroot.pem
rm newcsr.csr

And.. did it work?

# openssl verify -CAfile newroot.pem -verbose cert.pem
cert.pem: OK

But.. why? They're different files, right?

# sha1sum newroot.pem
62577e00309e5eacf210d0538cd79c3cdc834020  newroot.pem
# sha1sum origroot.pem
c1d65a6cdfa6fc0e0a800be5edd3ab3b603e1899  origroot.pem

Yes, but, that doesn't mean that the new public key doesn't cryptographically match the signature on the certificate. Different serial numbers, same modulus:

# openssl x509 -noout -text -in origroot.pem
        Serial Number:
            c0:67:16:c0:8a:6b:59:1d
...
            RSA Public Key: (1024 bit)
                Modulus (1024 bit):
                    00:bd:56:b5:26:06:c1:f6:4c:f4:7c:14:2c:0d:dd:
                    3c:eb:8f:0a:c0:9d:d8:b4:8c:b5:d9:c7:87:4e:25:
                    8f:7c:92:4d:8f:b3:cc:e9:56:8d:db:f7:fd:d3:57:
                    1f:17:13:25:e7:3f:79:68:9f:b5:20:c9:ef:2f:3d:
                    4b:8d:23:fe:52:98:15:53:3a:91:e1:14:05:a7:7a:
                    9b:20:a9:b2:98:6e:67:36:04:dd:a6:cb:6c:3e:23:
                    6b:73:5b:f1:dd:9e:70:2b:f7:6e:bd:dc:d1:39:98:
                    1f:84:2a:ca:6c:ad:99:8a:fa:05:41:68:f8:e4:10:
                    d7:a3:66:0a:45:bd:0e:cd:9d
# openssl x509 -noout -text -in newroot.pem
        Serial Number:
            9a:a4:7b:e9:2b:0e:2c:32
...
            RSA Public Key: (1024 bit)
                Modulus (1024 bit):
                    00:bd:56:b5:26:06:c1:f6:4c:f4:7c:14:2c:0d:dd:
                    3c:eb:8f:0a:c0:9d:d8:b4:8c:b5:d9:c7:87:4e:25:
                    8f:7c:92:4d:8f:b3:cc:e9:56:8d:db:f7:fd:d3:57:
                    1f:17:13:25:e7:3f:79:68:9f:b5:20:c9:ef:2f:3d:
                    4b:8d:23:fe:52:98:15:53:3a:91:e1:14:05:a7:7a:
                    9b:20:a9:b2:98:6e:67:36:04:dd:a6:cb:6c:3e:23:
                    6b:73:5b:f1:dd:9e:70:2b:f7:6e:bd:dc:d1:39:98:
                    1f:84:2a:ca:6c:ad:99:8a:fa:05:41:68:f8:e4:10:
                    d7:a3:66:0a:45:bd:0e:cd:9d

Let's go a little further to verify that it's working in real world certificate validation.

Fire up an Apache instance, and let's give it a go (debian file structure, adjust as needed):

# cp cert.pem /etc/ssl/certs/
# cp origroot.pem /etc/ssl/certs/
# cp newroot.pem /etc/ssl/certs/
# cp cert.key /etc/ssl/private/

We'll set these directives on a VirtualHost listening on 443 - remember, the newroot.pem root certificate didn't even exist when cert.pem was generated and signed.

SSLEngine on
SSLCertificateFile /etc/ssl/certs/cert.pem
SSLCertificateKeyFile /etc/ssl/private/cert.key
SSLCertificateChainFile /etc/ssl/certs/newroot.pem

Let's check out how openssl sees it:

# openssl s_client -showcerts -CAfile newroot.pem -connect localhost:443

Certificate chain
 0 s:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=server.lan
   i:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=root
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
 1 s:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=root
   i:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=root
-----BEGIN CERTIFICATE-----
MIICHzCCAYgCCQCapHvpKw4sMjANBgkqhkiG9w0BAQUFADBUMQswCQYDVQQGEwJB
...
-----END CERTIFICATE-----
(this should match the actual contents of newroot.pem)
...
Verify return code: 0 (ok)

Ok, and how about a browser using MS's crypto API? Gotta trust the root, first, then it's all good, with the new root's serial number:

newroot

And, we should still be working with the old root, too. Switch Apache's config around:

SSLEngine on
SSLCertificateFile /etc/ssl/certs/cert.pem
SSLCertificateKeyFile /etc/ssl/private/cert.key
SSLCertificateChainFile /etc/ssl/certs/origroot.pem

Do a full restart on Apache, a reload won't switch the certs properly.

# openssl s_client -showcerts -CAfile origroot.pem -connect localhost:443

Certificate chain
 0 s:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=server.lan
   i:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=root
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
 1 s:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=root
   i:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=root
-----BEGIN CERTIFICATE-----
MIIC3jCCAkegAwIBAgIJAMBnFsCKa1kdMA0GCSqGSIb3DQEBBQUAMFQxCzAJBgNV
...
-----END CERTIFICATE-----
(this should match the actual contents of origroot.pem)
...
Verify return code: 0 (ok)

And, with the MS crypto API browser, Apache's presenting the old root, but the new root's still in the computer's trusted root store. It'll automatically find it and validate the cert against the trusted (new) root, despite Apache presenting a different chain (the old root). After stripping the new root from trusted roots and adding the original root cert, all is well:

oldroot

So, that's it! Keep the same private key when you renew, swap in the new trusted root, and it pretty much all just works. Good luck!

Best Answer

Related Solutions

Unrevoke a certificate which was revoked with a status different from Certificate Hold

OpenSSL – Certification Authority Root Certificate Expiry and Renewal

Related Topic