Re: [hybi] Handshake was: The WebSocket protocol issues.

[Scott Ferguson <[e-mail]>]

Greg Wilkins wrote:
> On 28 September 2010 09:26, Scott Ferguson <[e-mail]> wrote:
>   
>> Greg Wilkins wrote:
>>     
>>> Scott,
>>>
>>> yes - I glossed over the details of what the actual hash should be in
>>> the ping packet.  I believe H(c-nonce, "WebSocket") is a good hash
>>> that indicates the server is a WS.
>>>       
>> That's not quite the issue. It's the second hash in the PONG that's missing,
>> because we also need to verify the client as a WS client and not a hijacked
>> HTTP client (or hijacked future non-websocket client):
>>     
>
> OK, I've got it.
>
> For your proposal of a server nonce, then a HELLO op-code is more
> appropriate than ping/pong as the pong should normally contain the
> same content as the ping.
>
> So my proposal was:
>
> HTTP(upgrade,nonce)   -->
> <-- HTTP(101)
> <-- WS(ping,hash(nonce,"WebSocket"))
> [ <-- * WS(op, data)  ]
> --> WS(pong,hash(nonce,"WebSocket"))   ; client calls onOpen
> [ * WS(op, data) -->  ]
>
>
> Your amendment is
>
> HTTP(upgrade,c-nonce)   -->
> <-- HTTP(101)
> <-- WS(hello,hash(c-nonce,"WebSocket"),s-nonce)
> [ <-- * WS(op, data)  ]
> --> WS(hello,hash(s-nonce,"WebSocket"))   ; client call onOpen
> [ * WS(op, data) -->  ]
>   

Exactly.

>
> I'm not 100% convinced that the server nonce is really necessary, as
> the client has already been validated by sending Sec-Headers and the
> upgrade in the first place, and the contents of the ping message must
> be copied into a pong message (and is not predictable if the nonce is
> hidden from the client).
>
> But if we want defence in depth, then the second hash of a s-nonce is
> an good way to achieve this.
>   
Yep.

The s-nonce gives the server control over the validation of the client, 
because the server controls the quality of the s-nonce. Otherwise, it 
would be relying on the quality of hijacked client's c-nonce and the 
client's own headers to validate the client. Since the client validation 
protects the websocket server, it makes sense for the server to have 
that control.

-- Scott
> cheers
>
>
>
>