TLS ALPN Proposal v5

Simone Bordet simone.bordet at
Fri Sep 25 14:20:40 UTC 2015


On Fri, Sep 25, 2015 at 3:20 PM, Xuelei Fan < at> wrote:
> For the complication, I posted the comments in previous mail here:
> -----------------------------
>> In case you have [HTTP/2, AP_NEW, HTTP/1.1], then you can simply
>> compose the comparators to sort first with the H2.CIPHER_COMPARATOR,
>> cipherSuites = Arrays.sort(cipherSuites,
>>        ApplicationProtocol.H2.CIPHER_COMPARATOR.
>>        thenComparing(AP_NEW.CIPHER_COMPARATOR));
> Let's look at an example.  application_protocol_1 prefer cipher_suite_1,
> and application_protocol_1 prefer cipher_suite_2.
> The comparator for application_protocol_1 would set the preference as
> {cipher_suite_1, cipher_suite_2}.  and the comparator for
> application_protocol_2} would set the preference as {cipher_suite_2,
> cipher_suite_1}.
> The result to sort 1 and then 2, and the result to sort 2 and then 1 are
> different.
> The call sequence to the comparators, and the call to each comparator
> would result in difference result.  That's may be not the expected behavior.

The example is malformed, since it does not specify which ciphers are
good for which application protocol, and neither the order of the
application protocols.

Let me rewrite it:

application protocols: [ap1, ap2]
ciphers: [c1, c2]

ap1 requires c1, does not work with c2
ap2 requires c2, does not work with c1

Now the question is: you have to configure your system, what you want to do ?

If you want to favor ap1, then you sort [c1, c2]
If you want to favor ap2, then you sort [c2, c1]
If you want to favor c1, then you sort [c1, c2]
If you want to favor c2, then you sort [c2, c1]

If you want to favor ap1 *and* c2, you have to decide what is more
important between the two, because you cannot have both.

I don't see any problem, really.

That the results are different, sure, but they are predictable.
When the configuration uses one comparator, it will always be that
result, and same for the other comparator.

But you configure the comparators in base of what you want to do.

Simone Bordet
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless.   Victoria Livschitz

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