PTK Rotation in WPA-PSK and WPA2-PSK

[essel]

Hi,

I made some researches about how WPA-PSK (using TKIP) and WPA2-PSK (using AES) are working. What I learned is that both produce a PMK (Pairwise Master Key) and a PTK (Pairwise Transient Key). This latter key is produced using, in
part, the PMK, the MAC address of both communicating systems, and random
values.

What I understand from those researches, it is that the AES algorithm seems to be more secure because the seed used to generate the random values (for the production of the PTK renewals) is changed more often than the seed in TKIP (using the RC4 algorithm).

Is that making sense?

If yes, how often this seed is changed in the AES compared to the TKIP (RC4)?

Thanks for having taken the time to read.

- essel

[Ridirich]

Well, let's ask Mr. Google.

Hope that helps. I found the equasion to what you are looking for in there, so now it's up to you.

[essel]

Hi Ridirich,

Thanks for your reply and your Google search.

From those links, I learned that WPA (TKIP – RC4) and WPA2 (AES) both renew their keys on a per-packet basis.

But, is the seed used to generate those keys also change on a per-packet basis or more often?

Since I'm not very good at reading all the algorithm graphics, I not sure if I interpret them well enough.

I simply try to find if the fact that WPA (TKIP – RC4) change is seed less frequently than WPA2 (AES) is true or false.

- essel

[Ridirich]

It is changed more frequently in the WPA2

[essel]

Hi Ridirich,

So, the fact that WPA (TKIP – RC4) changes the seed less frequently than WPA2 (AES) is not a myth but a reality.

I read again some of the links you provided to me and I continued my research. My new founds (and understanding) is that the AES change its seed on a per-block (of data within a single packet) basis. And, depending on a fact that I don't quite understand right now, the length of a single block of data is the same for an entire packet, but can be of a different length from packet to packet (or from message to message).

Is that makes sense? Am I on the right track?

Thanks for your help and time.

- essel