In adding a debian10 Evergreen build variant to the C driver I encountered unexpected failures in SSL-related tests. Debian 10 ships with OpenSSL 1.1.1c.

I dug around this a bit and added a call to "ERR_print_errors_fp (stderr);" just before the driver emits the error message that was displayed, and this is what is on the libssl error stack:

[2019/09/21 16:09:58.204] 140374663296768:error:140AB18E:SSL routines:SSL_CTX_use_certificate:ca md too weak:../ssl/ssl_rsa.c:310:
[2019/09/21 16:09:58.204] 2019/09/21 20:09:58.0204: [25219]: ERROR: mongoc: Cannot find certificate in 'src/libmongoc/tests/x509gen/server.pem'

The solution appears to be certificates with stronger crypto for the SSL-related tests.