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Re: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned

Andrei Popov <Andrei.Popov@microsoft.com> Mon, 13 April 2015 21:32 UTC

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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: "mrex@sap.com" <mrex@sap.com>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned
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Date: Mon, 13 Apr 2015 21:32:22 +0000
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Archived-At: <http://mailarchive.ietf.org/arch/msg/tls/Ee8vXNvmgH8rzf2izu9druh8pk4>
Subject: Re: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned
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Hi Martin,

Although the currently defined ALPN IDs consist of printable characters (which admittedly helps when looking at network traces), generally speaking ALPN IDs are octet strings and could contain arbitrary bytes.

Cheers,

Andrei

-----Original Message-----
From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Martin Rex
Sent: Monday, April 13, 2015 2:18 PM
To: tls@ietf.org
Subject: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned

I have only recently looked at the TLS extension ALPN spec (RFC7301) and it seems that there currently is no reserved character for the ALPN ID registry that could be used as seperator character if one wanted to facilitate the admin/user UI and tracing/logging.

While I don't allowing UTF8, I would have really appreciated reserving at least one character (or octet value) for the obvious purpose of printing all currently offered protocols in a single line.

I'm also puzzled why the octet value 0 was not banned from the ALPN ID either.  That seems like calling for trouble.

-Martin

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