Mass encryption use, and DPI

[Peter Fairbrother]

Peter Fairbrother wrote:
> Ian Batten wrote:
>>
>> On 21 Jun 2009, at 04:50, Peter Fairbrother wrote:
>>
>>> The HO seem to be (maybe... ) continuing with their attempt to log 
>>> all comms between everyone, eg those messages passed via facebook or 
>>> whatever, using DPI - but just how hard would it be for facebook etc 
>>> to use SSL encryption?
>>>
>>> That would be transparent to the user, but just how much would it 
>>> cost facebook to implement? 0.001%?  1%?
>>
>> At risk of returning this list to discussing crypto, isn't one of the 
>> problems going to be, for a seriously high-traffic site like Facebook, 
>> laying hands on enough entropy to make the server end of the key 
>> negotiation secure?
>>
>> ian
> 
> Leaving aside hardware RNG's, I think, for client-side security, the 
> server hardly needs any entropy at all.
> 
> The RSA bit needs none, and server could reuse the DH entropy as often 
> as needed, relying on the client to provide secure entropy.

Been looking into TLS, and the server doesn't actually need any entropy 
at all unless DH is used. It does send a random number, but it's sent in 
the clear and there is no DH secret behind it. so it doesn't have to be 
truly CS-random, and in almost all cases it can be reused and changed 
every minute or so without impacting security.

And as above, any DH secret can be reused, so the entropy required is 
minimal.

> 
> Which just leaves the cost of the hardware...

Been looking for data on this, can't seem to find anything useful. It 
seems that Facebook average 580 connections per second, and have an 
average of about 800,000 people connected.

These figures came from different sources, and don't jibe very well - 
the average connection would last 20 minutes, which seems overlong, and 
the burden would be on the symmetric encryption rather than the setup - 
but I'll use them anyway to get some idea.

Using HP AXL300 cards they'd need about 120, costing £35,000, for 2kbit 
RSA and DH setup. For symmetric encryption they'd need a million or so 
for asics - or if they used 8800GTX cards for both, that would come to 
about £100,000 for hardware.

Unless I have made a mistake, even adding in power and extra crypto 
personnel costs, it's not a lot of money for Facebook!

-- Peter Fairbrother