> Here’s why I picked PPTP and I believe using it with very long passwords/passphrases is acceptable.
Bear in mind that the author is looking to use this in open hotspots such as coffee shops etc. I would not advise that people implement this.
As the author points out, there are a number of vulnerabilities in PPTP, the most serious of which is that the initiation protocol is susceptible to an offline brute force attack using tools like asleap[1].
To be clear, the attacker does not need a rogue access point, nor association with an access point for this to work. They can just passively sniff away, then at some point later go through the pcaps, crack it offline and do what they want. There's an episode of Hak5[2] covering this as well as this useful straight to the point video of asleep and THC pptp-bruter[3]
Author here. Like I said in the post, the third constraint I had was something that would work with dd wrt - and that doesn't support l2tp. Thanks for the bit on the offline cracking though.
No worries, I understand your reasons for choosing PPTP, but I thought it important to highlight the consequences.
It is clear you have put a lot of effort into it though and it's more well written than a lot of guides I've seen, hence my interest in the first place!
How large is the risk of an offline attack if I choose a 16 character mixed case alphanumeric randomly generated password? Is there much of an exposure in that case?
The characters are largely irrelevant. If an attacker is an opportunist and (for example) just wants to run any traffic passing his house through something quick and dirty then it's going to boil down to whether or not his wordlist contains your password.
If the adversary is reasonably well organised they might use something like AWS to offload the cracking, in which case they may well expend more resources on a bigger and more wordlist. Cloud-based cracking is really interesting, especially when GPU support comes into play as most of the traditional models of attack complexity fall like a house of cards once your average joe can get the kind of supercomputing power only previously available to three letter agencies.
In all honesty I would just avoid PPTP and stick to L2TP or an SSL-based VPN. In TFA the author chose PPTP because he wanted to stick what was available on his router and compatible with his devices. I understand their decision, although personally I don't see this as being any more secure than running a password protected browser-based file manager and port forwarding it to the world. You'd still have to obtain a password, but it's not hard.
> Here’s why I picked PPTP and I believe using it with very long passwords/passphrases is acceptable.
Bear in mind that the author is looking to use this in open hotspots such as coffee shops etc. I would not advise that people implement this.
As the author points out, there are a number of vulnerabilities in PPTP, the most serious of which is that the initiation protocol is susceptible to an offline brute force attack using tools like asleap[1].
To be clear, the attacker does not need a rogue access point, nor association with an access point for this to work. They can just passively sniff away, then at some point later go through the pcaps, crack it offline and do what they want. There's an episode of Hak5[2] covering this as well as this useful straight to the point video of asleep and THC pptp-bruter[3]
[1] http://www.willhackforsushi.com/Asleap.html [2] http://revision3.com/hak5/asleap [3] http://blip.tv/g0tmi1k/cracking-vpns-asleap-and-thc-pptp-bru...
The solution is to use L2TP and IPSec if you can and aren't jailbreaking, or to use a TLS VPN if you have jailbroken or don't have iDevices.