Can not specify cipher list of just 'TLSv1.3'

[jkman340@…]

I was testing different scenarios with using TLSv1.2 and TLSv1.3 and I can across a strange issue when specifying just TLSv1.3 for the cipher list.

For example, in my site if i set the following:

ssl_protocols TLSv1.3;
ssl_ciphers TLSv1.3;

The server fails to start with the error:
nginx: [emerg] SSL_CTX_set_cipher_list("TLSv1.3") failed (SSL: error:1410D0B9:SSL routines:SSL_CTX_set_cipher_list:no cipher match)

However, I am able to specify the following:

ssl_protocols TLSv1.2;
ssl_ciphers TLSv1.2;

OR

ssl_protocols TLSv1.3 TLSv1.2;
ssl_ciphers TLSv1.2:TLSv1.3;

and the server will start successfully.

I am not sure why it is throwing an error on the first scenario, seems like a valid cipher list to me (And works with openssl).

[Maxim Dounin]

OpenSSL does not support "TLSv1.3" as a valid cipher string:

$ openssl version
OpenSSL 1.1.1d  10 Sep 2019
$ openssl ciphers TLSv1.3
Error in cipher list
0:error:1410D0B9:SSL routines:SSL_CTX_set_cipher_list:no cipher match:ssl/ssl_lib.c:2558:

Instead, all TLSv1.3 ciphers are enabled by default, and can be only controlled via a separate API, see #1529. If "TLSv1.3" works as a cipher list for you somewhere, this means that the error returned by SSL_CTX_set_cipher_list() is simply ignored.

In this particular case, there is no need to specify anything in ssl_ciphers, as non-TLSv1.3 ciphers won't be used with TLSv1.3 anyway.

[jkman340@…]

Thanks for the reply and pointing to #1529. After reading #1529 I see what you mean. I echo the one user's comments that the Nginx documentation should be updated to reflect that the 'ssl_ciphers' directive only applies to TLSv1.2 and earlier and TLSv1.3 ciphers are enabled by default.

Part of the issue too was I was running 'openssl ciphers TLSv1.3' on an Ubuntu Bionic system that was using OpenSSL v1.1.1, which does in fact return a valid list of TLSv1.3 ciphers. On this version you could also run 'openssl ciphers gibberish' and it would return the same result. Even though 'gibberish' is not a valid cipher string, the TLSv1.3 ciphers are always returned. This behavior changed in openssl 1.1.1b (​https://github.com/openssl/openssl/pull/7759). Now running 'openssl ciphers TLSv1.3' or 'openssl ciphers jibberish' now returns the error as seen above of 'no cipher match'.