Re: [TLS] Narrowing allowed characters in ALPN ?

Ben Schwartz <bemasc@google.com> Thu, 20 May 2021 14:40 UTC

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From: Ben Schwartz <bemasc@google.com>
Date: Thu, 20 May 2021 07:39:59 -0700
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To: "Salz, Rich" <rsalz=40akamai.com@dmarc.ietf.org>
Cc: Martin Thomson <mt@lowentropy.net>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Narrowing allowed characters in ALPN ?
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On Thu, May 20, 2021 at 6:30 AM Salz, Rich <rsalz=
40akamai.com@dmarc.ietf.org> wrote:

> Look at RFC 701, it says: the precise set of octet values that identifies
> the protocol. This could be the UTF-8 encoding of the protocol name.
>
> So I changed my mind and think it's okay to leave as-is but wouldn't mind
> if it became less general or more specific. For example, what if a protocol
> string matches a truncated UTF8 string?  It makes me think of SNI which
> could have any format, but really is "any format as long as it's a DNS name"
>

One intermediate option might be to keep the ALPN TLS extension 8-bit
clean, but change the IANA instructions for the ALPN registry to tighten
the registration requirements.