Changes by Antoine Pitrou pit...@free.fr:
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resolution: - fixed
stage: - resolved
status: open - closed
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Python tracker rep...@bugs.python.org
http://bugs.python.org/issue21013
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Donald Stufft added the comment:
I think I'm happy with this patch, if anyone has a chance to review it and see
if it looks OK I'd love that and then I can commit it :)
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Donald Stufft added the comment:
Added guards to protect against constants not existing.
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Added file:
http://bugs.python.org/file34590/ssl-context-defaults-ssl3-guards.diff
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Roundup Robot added the comment:
New changeset 92efd86d1a38 by Donald Stufft in branch '3.4':
Issue #21013: Enhance ssl.create_default_context() for server side contexts
http://hg.python.org/cpython/rev/92efd86d1a38
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nosy: +python-dev
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Python
Roundup Robot added the comment:
New changeset aa2eb034c4f7 by Donald Stufft in branch 'default':
Merge the patch for issue #21013 into default
http://hg.python.org/cpython/rev/aa2eb034c4f7
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Donald Stufft added the comment:
Attached is a patch that:
* Switches the protocol to SSLv23 so that we can negotiate a TLS1.1 or TLS1.2
connection.
* Sets OP_CIPHER_SERVER_PREFERENCE for Purpose.CLIENT_AUTH so that our
carefully selected cipher priority gives us better encryption and PFS
*
Changes by Alex Gaynor alex.gay...@gmail.com:
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Antoine Pitrou added the comment:
(as an aside, Donald, perhaps you want to consider adding yourself to relevant
topics in http://docs.python.org/devguide/experts.html )
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Donald Stufft added the comment:
I'll do that :)
To be clear about this patch, it raises the upper bounds of security by
enabling TLS 1.1, and 1.2 as well as the single use for (EC)DH and preferring
the server ciphers.
However it also lowers the lower bounds of security and includes SSLv3
Antoine Pitrou added the comment:
We can add OP_NO_SSLv3 to the default context to prevent SSL3 but it's
sort of a situational thing. If you're doing something where you need
SSL3 clients you don't want OP_NO_SSLv3.
So I guess the question is, do we want to be more secure by default
and
Alex Gaynor added the comment:
Unfortunately most TLS implementations (particularly those in browser stacks)
are vulnerable to downgrade attacks, whereby an attacker can send some
malicious packets to simulate a connection failure and cause a lower version of
the protocol to be negotiated,
Donald Stufft added the comment:
That's not entirely true unfortunately :(
There are downgrade attacks that work all the way up through TLS 1.2. These are
not strictly a problem of the protocol specs but instead of the implementations.
See:
Donald Stufft added the comment:
To be clear though, a lot of TLS servers out there still have SSL3.0 enabled by
default, primarily because of IE6 / XP. I'm on the fence about what the right
answer is for create_default_context. From a strictly best practices for
security sense of view you
Antoine Pitrou added the comment:
(by which I mean: ok, let's disable SSLv3)
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Antoine Pitrou added the comment:
Well, I suppose IE6/XP is starting to look very old (though probably deployed
quite widely), and TLS 1.0 was standardized in 1999.
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Donald Stufft added the comment:
Attached is a new patch. It has:
* Switches the protocol to SSLv23 so that we can negotiate a TLS1.1 or TLS1.2
connection.
* Sets OP_CIPHER_SERVER_PREFERENCE for Purpose.CLIENT_AUTH so that our
carefully selected cipher priority gives us better encryption and
New submission from Antoine Pitrou:
Currently, create_default_context() doesn't do anything special for server use.
It seems the configuration could be improved, though:
- PROTOCOL_TLSv1 is suboptimal for servers: a TLSv1 server can't accept a
TLSv1.2 client, but a SSLv23 server will; so we
Antoine Pitrou added the comment:
(also perhaps enable OP_CIPHER_SERVER_PREFERENCE, although it seems it could
cause interoperability problems with some clients)
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Donald Stufft added the comment:
Nah it should be fine to enable that, and it's preferable to do so. The server
selects the cipher anyways in the TLS handshake. That just tells the server to
prefer it's list for precedence and not the client list.
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