Re: [TLS] Fallback SCSV summary

["Yngve N. Pettersen" <[e-mail]>]

On Mon, 10 Nov 2014 17:48:24 +0100, Hubert Kario <[e-mail]> wrote:

> On Saturday 08 November 2014 04:37:51 Yngve N. Pettersen wrote:
>> Hello all,
>>
>> Below is some statistics that I did not complete gathering until this
>> week, related to something I think was mentioned in the SCSV discussion
>> thread a couple of weeks ago: Some servers are apparently intolerant to
>> the SCSV, and attempts to connect using the SCSV will fail.
>>
>> My TLS Prober runs indicates that 2.5% of servers will fail a connection
>> using the SCSV when it is placed at the last position in the cipher  
>> suite
>> list, and 4.9% will fail if it is placed at the beginning of the list.
>
> I'm assuming you mean a test with ClientHello that otherwise includes  
> ciphers
> that were verified as supported by server, includes the RC4 ciphers in  
> the
> first 64 ciphers and is smaller than 256 bytes.
>
> In other words, tested in a way that won't trigger other common bugs.

The Client Hellos in this case are usually smaller than 160 bytes, and  
includes the same cipher suites and extensions that the server was tested  
with originally to determine support for the TLS version and support for  
extensions. IOW, the Client Hello is just 2 bytes longer than those  
original Hellos.

For reference, 13% of the servers intolerant against the SCSV at the end  
were also failing a 256 byte Hello, and 8% of those failing at the start  
also failed the 256 byte test.

-- 
Sincerely,
Yngve N. Pettersen

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