Re: How to download over https

[Dan Purgert <dan@djph.net>]

Pascal Hambourg wrote:
> Le 18/06/2016 18:19, Dan Purgert a écrit :
>> Pascal Hambourg wrote:
>>> Le 17/06/2016 21:52, Jochen Spieker a écrit :
>>>> Pascal Hambourg:
>>>>>
>>>>> Hmm. I don't know how SSL works, but HTTPS runs on top of TCP so I doubt
>>>>> that it cares about IP packet size. The task of splitting the TCP payload
>>>>> stream into IP packets is done by the TCP layer.
>>>>
>>>> Sure, but if your encryption scheme wastes payload in yout packets you
>>>> have more overhead for TCP/IP headers in each packet.
>>>
>>> Why would encryption increase the payload size ?
>>> Disk encryption with dm-crypt does not (except for the LUKS header).
>>
>> Because most encryption schemes use a standard blocksize (let's say 64
>> bytes), and those 'encrypted blocks' do not fit well into the max
>> payload size of a packet.
>>
>> More packets = more overhead.
>
> Again, why would whole encrypted blocks need to fit in packets ? TCP is 
> a stream-oriented transport protocol, so the encryption block size and 
> boundary does not matter.

Because the TCP "stream" is still encapsulated in IP packets / Ethernet
frames, and you cannot simply "break" an encrypted block at some
arbitrary point in order to make it fit nicely in the packet / frame.

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