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[TLS] Encrypting ALPN and other unused extensions

Watson Ladd <watsonbladd@gmail.com> Fri, 25 April 2014 14:53 UTC

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From: Watson Ladd <watsonbladd@gmail.com>
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Subject: [TLS] Encrypting ALPN and other unused extensions
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Dear all,
Some extensions aren't used by the TLS layer, like ALPN. One of the
goals is to encrypt them. However, in a zero-RTT handshake this will
require knowing a server key to encrypt them with. In a one-RTT
handshake one can do the same thing.

The challenge is the case where the client knows nothing about the
server: here it cannot be encrypted until after the client hears from
the server, and since this is a negotiation, another round trip after
that.

Having the server make the offer and the client accept one fits nicely
into the 1-RTT handshake with no problems. However, this is not what
we decided to do with ALPN.

Any ideas?

Sincerely,
Watson Ladd

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