Certificate with compromised key / *.digicert-demo.com

[Hanno Böck]

Hi,

I discovered a certificate with a compromised key. While this would
usually be an uninteresting event, I think this one is a bit more
unusual.

This certificate
https://crt.sh/?id=15456747789
issued by Digicert for *.digicert-demo.com uses this key (a test key
from OpenSSL's source code):
https://github.com/openssl/openssl/blob/master/test/certs/leaf.key

As this is a hostname that is owned by the CA itself, it makes me
wonder how this happened.

The certificate was revoked quickly after I reported it to Digicert.

--
Hanno Böck - Independent security researcher
https://itsec.hboeck.de/
https://badkeys.info/

[Tim Hollebeek]

Thank you Hanno for bringing this to our attention. It turns out one of our sales engineers used this key pair to issue a certificate during a demonstration. Since it wasn't in the blocklist, it issued.

We have about 1.5M key pairs in our blocklist, but there are a lot of places to look for key pairs, and we hadn't searched OpenSSL for them. We did that today in response to your discovery.

As an aside, I'd like to encourage people to use the RFC 9500 test keys, where feasible, instead of generating new ones. This makes it much easier to block test keys in a more comprehensive way.

We have added the OpenSSL private keys that were not already present on our key blocklist. For CAs who track external blocked keys, here is a list of OpenSSL private keys:

https://github.com/openssl/openssl/tree/master/test/certs.

For general awareness, we also maintain a page where compromised private keys may be reported:
https://problemreport.digicert.com/.

-Tim

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[Mike Shaver]

Possibly of interest in blocking keys is Matt Palmer's great work in this space: https://pwnedkeys.com/

Mike

To view this discussion visit https://groups.google.com/a/mozilla.org/d/msgid/dev-security-policy/SN7PR14MB6492725DDF463B136D208B23832F2%40SN7PR14MB6492.namprd14.prod.outlook.com.