Re: TCP timestamp starting value

[Mihai Chelaru <chelaru%gmail.com@localhost>]

On 28/07/16 21:15, Joerg Sonnenberger wrote:
> On Tue, Jul 26, 2016 at 10:23:44AM -0400, Thor Lancelot Simon wrote:
>> On Tue, Jul 26, 2016 at 12:09:04PM +0200, Joerg Sonnenberger wrote:
>>>
>>> MD5 or any other cryptographic hash.
>>
>> I think this is too expensive.  Consider a system which initiates 300,000
>> TCP connections per second (I have built NetBSD-based products that were
>> in this ballpark, at least as a design goal).  With IPv6 addresses, that
>> is 40 bytes per connection, or 12MB/sec of MD5.
>>
>> That's between 5% and 10% of a modern CPU core.  Using a modern cryptographic
>> hash would make it much worse.  Do we really want to burn that for this
>> reason?
> 
> I'm not sure what the best hash function is here. Anything with a good
> avalanche effect should work and we certainly don't need the output size
> of "normal" cryptographic hash functions. Just something preimage
> resistent would work here.
> 
> Joerg
> 

Is there a reason for which we cannot re-use iss for the timestamp offset ?