Thread: Maemo 5 as a vulnerability / "hacking" victim
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momcilo is offline momcilo
2011-06-16 , 21:19
Posts: 673 | Thanked: 856 times | Joined on Mar 2006
#41
Originally Posted by fasza2 View Post
You got me confused now I had to check my .conf file; but
I think tls-auth /etc/openvpn/ta.key 1 stands for the dynamic one.
So the preshared ta.key file is needed probably for this very reason:
I should have been more precise. That configuration is static because both side know shared secret. This secret is never changed unless you change it manually on both sides.

Originally Posted by fasza2 View Post
In fact, I'm not really sure what the static key mode is. Is it the non-PKI one?
Just read the following:
http://openvpn.net/index.php/open-so...mentation.html

Originally Posted by fasza2 View Post
Now I'm not sure how exacly they implemented this; if hash is encryped seperate from data or together. But I know if an attacker changes a single bit in the packet the hash will fail.
I've stumbled somewhere on explanation of protocol, that states the payload is encrypted than HMAC-ed. The problem is that the HMAC value is known to attacker as well. In order to exploit it the attacker has to know the value of IV which is the pre-shared secrete between client and server, which allows creation of packets with valid HMAC.


Originally Posted by fasza2 View Post
The whole idea is that the server has to be able to be extract the hash from the packet in order to filter out dodgy UDP packets to save the cypher and the TCP/IP stack from further processing. Sort of not letting your 'pipe' get 'clogged'. Thankfully, this is just the first line of defence. That being said as long as the hash can be extracted from the packet it would be possible to encrypt them together, but I'll try to read up on this later.
Well its a handy pocket knife, not the double-handed sword.

Originally Posted by fasza2 View Post
PS: MD5 is not recomended due to vulnerabilities and some other problems.
SHA1 is getting fair share of attention as well.

There were some really good papers from Chinese regarding the reduction of brute-force attempts.
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