Re: [little OT] Licensing/Implementing in Cocoa/Obj-C
Re: [little OT] Licensing/Implementing in Cocoa/Obj-C
- Subject: Re: [little OT] Licensing/Implementing in Cocoa/Obj-C
- From: Stefan Pantke <email@hidden>
- Date: Wed, 7 Apr 2004 00:11:23 +0200
Am 06.04.2004 um 23:28 schrieb Allan Odgaard:
On 6. Apr 2004, at 22:56, Stefan Pantke wrote:
We implemented a licensing system based on public-key cryptography.
RSA is used to create a license and to very the license from within
the application.
How many bits do you use for the keys?
Users receive their license by means of a file, which includes all
data. In detail, it includes the client's details, the serial number
and a bit more stuff.
Moreover, the license file is signed as well using RAS. Thus the
application can verify, if the license file is authentic. Thus,
it can't be changed by even a bit - then the digital signature would
break.
Your may set the key's size. The entire license file is around
200 bytes longer than the signing data.
Most likely the user will receive the serial number via email and it
shouldn't be too long, and will be base64 encoded (or perhaps even
base32 encoded) -- that puts a damper on the number of bits and thus
the security.
512 byte keys generate roughly 700 bytes of license information.
The license file itself is readable - thus the user can check his
information if needed, you can inspect it, if you like to, and
the user can send the license file back to you as prove of ownership.
I once followed the bulletin board of a cracker site (to get some
insight in their workings), and a lot of applications with even 128
bit keys were cracked routinely, although the attack seemed to be on
the random number generator (for creating the primes in the first
place). At least that was my take on it.
If you application will be cracked, I suppose you did a big job.
And thus, you will make big money ;-)
I expect the RSA stuff to be quite hard against cracking.
But to my knowledge there isn't such advanced crackers on the Mac, is
there? :) Although we did have a guy state he could break 128 bit AES
in no time, but hopefully he will only use this power for good... ;)
AES in such a short time? Quite interesting! Shouldn't he
join NSA?
Stefan
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