[issue21013] server-specific SSL context configuration

[Donald Stufft]

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: https://crypto.stackexchange.com/questions/10493/why-is-tls-susceptible-to-protocol-downgrade-attacks

The general gist of it is some servers/firewalls/etc have buggy implementations that cause a TLS1.0+ handshake to fail and some clients (browsers being a big one) decided to handle this by restarting the connection with SSL3.0 instead of TLS1.0+. So thus it is possible to effectively downgrade a client, even one that supports TLS1.2. It is not however possible to do it within a single connection.

The version selection process should not be considered a security feature but should instead be looked at as a way to opportunistically add newer features.

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<http://bugs.python.org/issue21013>
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