[issue20995] Use Better Default Ciphers for the SSL Module

[Donald Stufft]

Donald Stufft added the comment:

Ok Antoine I've looked around.

Using a string like this:

ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:ECDH+RC4:DH+RC4:RSA+RC4:ECDH+HIGH:DH+HIGH:RSA+HIGH:!aNULL:!eNULL:!MD5:!DSS

The only *additional* ciphers that get added from the use of HIGH are various Camellia ciphers. These ciphers are not known to be insecure at this point in time so as of right now this is not an insecure cipher string.

However I still content that using HIGH in the cipherstring actually adds additional maintenance burden. In order to know if that cipherstring is still safe you must run it against every target OpenSSL you want to make secure to ensure that it doesn't allow a new cipher that doesn't meet the security strength that was attempted to be had with that cipherstring. If you use an explicit cipher string then you know exactly which cipher suites Python will use no matter what the OpenSSL claims is HIGH or not. This means that instead of having to monitor all the various OpenSSL versions for new ciphers you only have to periodically check that the suites that Python selected are still secure.

Remember the "failure" mode for not having a cipher in the list is that a different cipher is selected unless there are no other ciphers. A New cipher being added to OpenSSL is not going to be the only cipher available in any meaningful timeframe. The "failure" mode for having a bad cipher in the list is possibly making the users of Python insecure. That's why an explicit approach is preferred over an open ended approach. Because you don't have to audit a moving target.

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<http://bugs.python.org/issue20995>
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