Support self-signed certificate

[devnibo]

My Problem

I generated a self-signed certificate and tried using that to connect via TLSv1.3 to a server written with libtls from libressl (written by me; just a test project).

When connecting/reading to/from the server I get the following error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: InvalidCertificate(Other(CaUsedAsEndEntity))', src/lib.rs:84:36

where the line src/lib.rs:84 contains client.process_new_packets().unwrap();. client is a ClientConnection.

The reason for this error seems to be that I use a self-signed certificate.

My research

In my research I found the issue https://github.com/briansmith/webpki/issues/114 from the original webpki repo. From the discussion in that issue I learn that connecting via a self-signed certificate is known to be not supported and that there is more important work to do before implementing it.

My question

Is there a will and time to implement connecting via a self-signed certificate in this repo?

Additional infos

I generated my certificate like this:

openssl req -subj "/CN=192.168.2.30" \
  -x509 -nodes -newkey rsa:4096 -sha256 \
  -config /etc/ssl/openssl.cnf \
  -keyout signed.key -out signed.crt

Running openssl x509 -in signed.crt -noout -text gives the following output:

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            cb:ca:a7:2d:e0:d2:90:44
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=192.168.2.30
        Validity
            Not Before: Nov  4 13:08:18 2023 GMT
            Not After : Dec  4 13:08:18 2023 GMT
        Subject: CN=192.168.2.30
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (4096 bit)
                Modulus:
                    00:e2:af:9b:ee:b7:7d:f2:b8:be:36:be:f7:11:7a:
                    5d:f5:a2:fc:b1:c2:6e:c7:78:23:29:f4:fc:40:7a:
                    3e:da:73:52:ec:66:93:2f:fc:b9:04:a5:d7:9e:af:
                    79:49:8c:2d:45:15:1b:38:da:8b:a5:96:3a:b0:e0:
                    04:c8:e5:6e:1c:fc:f1:97:d1:b7:88:e7:50:3b:d8:
                    e3:bd:bb:34:5e:5e:6f:f6:23:cd:78:ca:3b:07:ba:
                    24:1a:97:23:4b:e7:ea:de:71:e9:54:24:9f:d5:4e:
                    c0:9c:4a:d7:40:46:1a:48:57:c2:df:54:95:73:b3:
                    0d:20:a5:4f:dc:3f:ef:e2:7e:a4:1e:dd:1d:2c:c1:
                    ab:67:49:cc:47:22:aa:de:f7:e5:2b:8d:a6:b8:97:
                    66:72:dc:d6:b2:d8:63:33:f0:26:b3:62:86:e9:e0:
                    7d:63:04:5c:1d:cb:a9:e6:a2:d6:14:26:e0:e4:41:
                    c7:bd:bd:a4:45:d4:a8:84:9f:d8:17:2a:e6:ac:ca:
                    99:b9:4c:a0:2f:90:77:1a:73:24:82:cd:e4:90:79:
                    9e:37:ae:b9:39:ec:f0:09:35:ae:b3:14:25:a9:6f:
                    8b:e9:c7:67:59:89:f6:0d:40:40:ce:fa:62:8a:99:
                    70:85:3e:c7:82:4f:30:b3:79:69:d0:a5:7b:9f:ad:
                    0a:bd:0f:59:41:9e:fc:5d:fd:c2:08:62:c3:1b:58:
                    18:28:c4:2a:ba:8a:6d:1e:d2:27:f9:31:98:89:d6:
                    1b:88:e2:84:f2:bb:33:66:d3:aa:8c:55:0f:7b:9e:
                    0c:9f:cf:29:f4:f0:c2:63:71:29:1d:7a:a1:62:ce:
                    fc:f0:cf:64:a2:55:36:dd:b9:42:c9:18:e2:f8:27:
                    b8:8c:bc:a8:7c:be:fe:3a:a5:dc:fb:e1:88:1b:fe:
                    86:69:90:bd:2f:eb:c4:be:ab:76:1e:94:9a:50:6b:
                    7b:7b:9d:c3:3c:ef:d4:39:3d:6c:bf:6f:c3:a5:27:
                    23:26:5b:b7:65:ee:44:09:eb:5a:22:68:70:72:08:
                    5c:a3:1c:dd:4f:0a:89:48:a0:72:fc:5f:a6:38:41:
                    21:a6:ea:b2:a9:8d:88:1c:e9:68:cc:b2:c4:0c:6f:
                    6c:0e:a4:38:96:08:d9:03:fc:01:f3:3c:9e:5c:21:
                    19:80:62:12:22:ca:f1:c1:38:c5:58:ad:7f:9c:57:
                    45:3e:07:ed:47:d5:63:7f:d0:fb:30:18:6b:06:31:
                    13:3e:7e:11:6c:93:9c:b8:a4:17:00:0e:4e:b9:81:
                    41:0c:03:a3:e8:3f:1c:b7:a5:96:93:1b:8d:65:97:
                    e6:90:f5:05:9c:47:83:c8:b2:7a:e0:9f:27:0e:04:
                    e6:6d:77
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                5B:DC:4F:76:6A:17:19:CD:23:C2:D1:AE:00:C1:F6:AC:3F:4B:FB:6B
            X509v3 Authority Key Identifier:
                keyid:5B:DC:4F:76:6A:17:19:CD:23:C2:D1:AE:00:C1:F6:AC:3F:4B:FB:6B

            X509v3 Basic Constraints: critical
                CA:TRUE
    Signature Algorithm: sha256WithRSAEncryption
         44:1d:60:72:9c:74:16:c4:51:82:e8:9f:2b:0b:25:23:97:10:
         a7:ca:e8:07:8a:62:af:04:2b:97:78:40:5c:de:cb:88:86:8e:
         79:63:35:1b:88:5e:b4:77:39:01:cb:15:ab:b2:a5:ed:52:91:
         93:1c:02:5e:9a:db:31:cf:4e:78:1c:69:e1:51:36:95:26:49:
         e2:2f:bf:8b:86:db:99:57:4b:55:72:15:1a:5d:77:af:0e:fa:
         23:3a:a3:b7:5d:cd:f9:9b:13:65:f0:f5:5c:4a:cf:ec:92:6f:
         22:6b:88:ae:55:f7:05:40:39:74:21:1c:1e:eb:3b:c1:e5:ba:
         af:4d:88:61:88:5c:d2:4a:40:48:45:26:65:1d:74:7d:9a:bc:
         fb:00:89:c9:83:99:68:2f:df:23:6c:5d:e6:86:5a:9d:98:a2:
         94:ef:99:a0:03:be:51:2a:06:a3:84:9b:9d:4a:ee:55:e3:9b:
         2b:0f:72:1c:e0:f0:62:f7:0c:bc:3d:75:c3:88:41:59:ae:41:
         46:12:54:73:7b:9e:0c:c2:55:6a:fb:9a:2b:69:44:2e:81:ad:
         1b:b5:ce:fe:d1:30:fd:3f:e8:79:24:79:b6:91:f7:73:0d:f3:
         06:d1:b9:fc:6c:42:40:11:99:39:a8:df:bb:8d:02:1a:df:90:
         a1:84:6c:7d:64:46:0e:71:73:fd:cd:9b:44:ef:b3:1d:a3:59:
         32:ff:68:70:ae:6d:aa:eb:99:c5:b6:78:6c:29:80:74:be:19:
         96:6c:8c:11:88:06:d0:75:7f:9e:e6:59:25:a8:26:05:b2:6e:
         c2:f8:eb:a9:58:98:4a:8b:e0:7f:9a:a9:ce:e4:20:91:24:39:
         e6:e3:80:70:ce:2f:17:2c:1d:7f:0a:e9:e8:13:0f:ca:f4:2b:
         b8:a4:0c:5a:c9:34:bf:46:48:b1:14:36:d9:fc:bf:7f:9d:a4:
         43:55:c5:6e:35:74:5d:83:d1:3b:9d:70:88:68:72:c8:60:39:
         aa:f2:ae:19:fa:14:e5:7d:f2:a5:bd:b1:a2:04:47:45:08:4d:
         77:ef:f4:16:a4:4b:aa:6b:e0:ff:6c:61:06:9a:2f:a4:65:eb:
         ed:ab:06:61:ee:a7:55:cc:c7:af:43:3a:46:6f:65:2e:ce:4e:
         07:13:2f:8f:51:47:0c:f4:56:7a:ff:51:4a:24:5d:46:e7:6b:
         8f:84:f4:5a:67:6f:4f:29:0f:fe:20:62:aa:9e:0b:19:6e:64:
         db:64:1e:b4:5f:2c:fc:a0:99:bb:48:1a:f8:f0:9e:18:ff:9d:
         4d:a4:fb:99:2a:f8:df:ce:83:84:3a:b6:9a:b8:08:dc:3f:60:
         fe:be:a2:9b:7c:a8:9f:3f

If there is something I can further do or test, please let me know.

[cpu]

Hi there, thanks for opening an issue with so much detail. Much appreciated.

The reason for this error seems to be that I use a self-signed certificate.

Is there a reason you have to use a self-signed certificate instead of generating a CA certificate and a separate end-entity certificate issued by the CA? It sounds like you are also the server operator and so could make that change right?

Is there a will and time to implement connecting via a self-signed certificate in this repo?

I can't speak for everyone, but from my perspective the answer is no. I don't think the utility of supporting self-signed certificates is worth the complexity it would bring to the path building logic and I don't have time personally to prioritize implementing or reviewing that work. I think webpki deliberately did not implement this feature and so the case to do so would have to be fairly strong.

[devnibo]

Thanks for the quick answer.

Is there a reason you have to use a self-signed certificate instead of generating a CA certificate and a separate end-entity certificate issued by the CA?

Ah I didn't know I can do that. I will try that.

I don't know who is supposed to close the issue. From my side it can be closed. BTW nice repo.

[cpu]

Ah I didn't know I can do that. I will try that.

Sounds good. A tool like Minica might make the job easier for you.

[thalesfragoso]

Can someone point me to the requirement that forbids cA: true certificates from being used as leaf certificates ?

I generated a self-signed certificate with cA: false and managed to get it verified by webpki without problems, so this CaUsedAsEndEntity error seems overly restrictive.

[djc]

To be clear, as I understand it the restriction is that webpki will not verify paths with a single certificate -- that is, where the entity to be verified itself is acting as the trust root.

[thalesfragoso]

@djc It's been a while since my comment, but I do believe I managed to get a "chain" of a single certificate verified by wepki. I just had to go out of my way to avoid openssl from setting the cA flag when generating a self-signed certificate.

To be clear, I used a single self-signed certificate as the end entity, and inserted the same certificate as a trust root in webpki.
It's been a while, so not sure if something changed in the meantime.