I am using a custom Python build, with the liboqs-openssl which is encapsulating pq-algorithms. I generated the certificates using the provided dilithium2 algorithm and wanted to create a simple SSL connection with a Python client and server.

Simplified client:

context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
_socket = socket(AF_INET, SOCK_STREAM, 0)
_socket = context.wrap_socket(_socket, server_hostname=hostname)

Simplified server:

context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
server = socket(AF_INET, SOCK_STREAM, 0)
server = context.wrap_socket(self.__server, server_side=True)

Now when I try to run the server and the client, I get the client error ssl.SSLError: [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:1129) and the server error ssl.SSLError: [SSL: NO_SHARED_CIPHER] no shared cipher (_ssl.c:1129).

I already tried printing out the ciphers with context.get_ciphers() on both ends, where they were identical. Also I tried manually setting it to the same cipher on both ends with context.set_ciphers('ECDHE-RSA-AES256-GCM-SHA384') which only gives me the same result.

Does anyone have an idea what the issue might be?


I'm not familiar with libqs-openssl, but

  • The documentation clearly says that the necessary cipher support is for TLS 1.3, while your code insists on using TLS 1.2
  • You are trying to use ciphers which require RSA certificate, even though you don't have a RSA certificate

This together means that there are no ciphers which could support the authentication method available with your certificate. In other words: no ciphers and therefore also no shared ciphers.

  • Hi Steffen, thanks for the answer!. The version actually seemed to be the issue. On the server side I changed it to PROTOCOL_TLS_SERVER. The reason I chose the RSA cipher is that the certificates are hybrid certificates, and therefore also support old ciphers. I thought in testing that would make it simpler. Like I said, I got a list with all available ciphers in context.get_ciphers(). I now get an error in the client side, saying certificate verify failed: IP address mismatch, certificate is not valid for ''. Do I need to whitelist localhost when creating the CA cert? – Robinbux May 10 at 10:56
  • @Robinbux: "I now get an error in the client side, saying certificate verify failed: IP address mismatch, certificate is not valid for ''" - Looks like your original question got successfully answered. What you ask now is a different question and should better be asked as a new question. But in short: the subject of the certificate (preferable subject alternative names) must match hostname from your client (this is usually not called "whitelisting"). Nothing is known about your certificate but obviously it does not cover the hostname. – Steffen Ullrich May 10 at 11:10
  • That's it, I needed to create an extension file that specifies the alt_names and feed that into openssl when signing the server certificate. It's all working now, thanks! – Robinbux May 10 at 11:49

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