macOS SecureTransport拒绝导入OpenSSL接受的证书

Question

I'm trying to fix a failing test in the urllib3 open source Python project.

This test is called test_client_no_intermediate and tries to use a X.509 certificate called client_no_intermediate.pem . The goal is to fail with a "unknown CA" error. The test works as expected with OpenSSL: the import succeeds and the certificate is rejected.

However, on macOS with SecureTransport, the import fails with Import/Export format unsupported. . What's surprising is that it fails consistently on my machine with macOS 10.13.5 and Xcode 9.4.1 but only fails intermittently in continuous integration with macOS 10.12 and XCode 8.3.

Here is the certificate:

-----BEGIN CERTIFICATE-----
MIIC/jCCAmegAwIBAgImFhgDOYh0mJSEggRYaDQ2VjgRdyAwkXmAV2KGITVEhiJw
UmBGKBgwDQYJKoZIhvcNAQELBQAwcTELMAkGA1UEBhMCRkkxDjAMBgNVBAgMBWR1
bW15MQ4wDAYDVQQKDAVkdW1teTEOMAwGA1UECwwFZHVtbXkxETAPBgNVBAMMCFNu
YWtlT2lsMR8wHQYJKoZIhvcNAQkBFhBkdW1teUB0ZXN0LmxvY2FsMB4XDTE3MDUx
MjE4MzQyNloXDTIxMTIxOTE4MzQyNlowdzELMAkGA1UEBhMCRkkxDjAMBgNVBAgM
BWR1bW15MQ4wDAYDVQQKDAVkdW1teTEOMAwGA1UECwwFZHVtbXkxFzAVBgNVBAMM
DlNuYWtlT2lsQ2xpZW50MR8wHQYJKoZIhvcNAQkBFhBkdW1teUB0ZXN0LmxvY2Fs
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCadkbPLXPfA1bNjgL9F6+rVLs3
uZdbXemHf1oKkT4q9uruZTQCTDFvvWHq32r6G8KV7MASariSz+bIgpx1euZEOmwu
cd+ULs0HMdfqorRa3MuUtKuIzYiQvCsv788VoNKjs+NNMIexO6p6S9E36ce2trze
BCmpYmi0WofO0bSwnwIDAQABo3sweTAJBgNVHRMEAjAAMCwGCWCGSAGG+EIBDQQf
Fh1PcGVuU1NMIEdlbmVyYXRlZCBDZXJ0aWZpY2F0ZTAdBgNVHQ4EFgQUbe9reSw2
C72JuGVpc+/L/O2hVjwwHwYDVR0jBBgwFoAUnltsnuh2mjtqqDWk2RNSwC7njHkw
DQYJKoZIhvcNAQELBQADgYEADlJp3uMKxgS2hgCK+JZV4qsXGuZ/rcHgq5qlrfg0
i76+wwZ6fs3WQe+zNgXbJnRviM0VScSUBM8IuclyovFWLvs0Z0piELtZ7KPwrDVf
5S5ynJHnJSG+sj4N6v+tvtpGDb1S3ueLQm79MGXv9pmbaYBmUJ0YSEnrScWy90Bv
Tno=
-----END CERTIFICATE-----

OpenSSL happily decodes it:

$ openssl x509 -noout -in client_no_intermediate.pem -text
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            16:18:03:39:88:74:98:94:84:82:04:58:68:34:36:56:38:11:77:20:30:91:79:80:57:62:86:21:35:44:86:22:70:52:60:46:28:18
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=FI, ST=dummy, O=dummy, OU=dummy, CN=SnakeOil/emailAddress=dummy@test.local
        Validity
            Not Before: May 12 18:34:26 2017 GMT
            Not After : Dec 19 18:34:26 2021 GMT
        Subject: C=FI, ST=dummy, O=dummy, OU=dummy, CN=SnakeOilClient/emailAddress=dummy@test.local
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:9a:76:46:cf:2d:73:df:03:56:cd:8e:02:fd:17:
                    af:ab:54:bb:37:b9:97:5b:5d:e9:87:7f:5a:0a:91:
                    3e:2a:f6:ea:ee:65:34:02:4c:31:6f:bd:61:ea:df:
                    6a:fa:1b:c2:95:ec:c0:12:6a:b8:92:cf:e6:c8:82:
                    9c:75:7a:e6:44:3a:6c:2e:71:df:94:2e:cd:07:31:
                    d7:ea:a2:b4:5a:dc:cb:94:b4:ab:88:cd:88:90:bc:
                    2b:2f:ef:cf:15:a0:d2:a3:b3:e3:4d:30:87:b1:3b:
                    aa:7a:4b:d1:37:e9:c7:b6:b6:bc:de:04:29:a9:62:
                    68:b4:5a:87:ce:d1:b4:b0:9f
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                6D:EF:6B:79:2C:36:0B:BD:89:B8:65:69:73:EF:CB:FC:ED:A1:56:3C
            X509v3 Authority Key Identifier:
                keyid:9E:5B:6C:9E:E8:76:9A:3B:6A:A8:35:A4:D9:13:52:C0:2E:E7:8C:79

    Signature Algorithm: sha256WithRSAEncryption
         0e:52:69:de:e3:0a:c6:04:b6:86:00:8a:f8:96:55:e2:ab:17:
         1a:e6:7f:ad:c1:e0:ab:9a:a5:ad:f8:34:8b:be:be:c3:06:7a:
         7e:cd:d6:41:ef:b3:36:05:db:26:74:6f:88:cd:15:49:c4:94:
         04:cf:08:b9:c9:72:a2:f1:56:2e:fb:34:67:4a:62:10:bb:59:
         ec:a3:f0:ac:35:5f:e5:2e:72:9c:91:e7:25:21:be:b2:3e:0d:
         ea:ff:ad:be:da:46:0d:bd:52:de:e7:8b:42:6e:fd:30:65:ef:
         f6:99:9b:69:80:66:50:9d:18:48:49:eb:49:c5:b2:f7:40:6f:
         4e:7a

But SecureTransport fails on this specific certificate:

$ security verify-cert -c cacert.pem
Cert Verify Result: CSSMERR_TP_NOT_TRUSTED
$ security verify-cert -c client_no_intermediate.pem
SecCertificateCreateFromData: Unknown format in import.

What is wrong in this certificate?

Answer 1

The only thing obviously "wrong" with the certificate is the serial number is 38 bytes long.

https://tools.ietf.org/html/rfc3280#section-4.1.2.2

Given the uniqueness requirements above, serial numbers can be expected to contain long integers. Certificate users MUST be able to handle serialNumber values up to 20 octets. Conformant CAs MUST NOT use serialNumber values longer than 20 octets.

While there is also guidance that non-conformant CAs exist, it's possible that Apple put in a limit lower than 38 bytes.

That wouldn't explain intermittency, but having a certificate which doesn't look "conformant" is always asking for unreliability.