4 ms·

Could someone explain to me the significance of having the keys as opposed to simply breaking A5/1 or A5/2 (Which is considered to be trivial)? Especially since

by hurin 12y ago

Could someone explain to me the significance of having the keys as opposed to simply breaking A5/1 or A5/2 (Which is considered to be trivial)? Especially since A5/3 (which is also known to be insecure at least theoretically) can be downgraded to either of those or even A5/0? Is the advantage solely that they don't need to intercept the traffic as a middleman to ask the target to downgrade?

kabouseng 12y ago
The difference would be, that with the keys you could just listen in and capture all the traffic. If you had to force cell phone connections to A5/0, you would have to: 1) Have to both receive and transmit. 2) Have a stronger connection than any other nearby cell towers. 3) Have a backbone connection back into the network so that you can actually negotiate phone calls to users connected to other cell phone towers. 4) Have to be able to handle multiple simultaneous connections. Some MITM spoof cell towers only establish a connection for the person of interest, and all other devices in the area loses connection. A pretty tell tale sign of a rogue base station operating in an area. So in short it is much easier just to have the keys...
- hurin 12y ago
  That's what I assumed (but I wondered if there was some other advantage I was missing). Are not all the ciphers breakable post collection anyways? Is it fair to say that this is effectively for the purpose of blanket non-targeted surveillance? Where by having the keys in their possession it gives them a shortcut for bulk analysis and saving CPU time that would otherwise be spent breaking encryption. And a cpu-processing-savings advantage justified cyber-attacking a foreign civilian corporation?
  - rkangel 12y ago
    With the keys, you can do data collection now, and cracking later. You can do mass interceptions and then decide which calls you want to look at.
    - hurin 12y ago
      >With the keys, you can do data collection now, and cracking later. Do the attacks on A5/1 require known plaintext? I was under the impression that they do not.
      - BuildTheRobots 12y ago
        My understanding was that the A5/1 attack (and massive rainbow table) not only relies on known plaintext but also requires you to get the _start_ of the communication.

by hurin 12y ago

kabouseng 12y ago

The difference would be, that with the keys you could just listen in and capture all the traffic. If you had to force cell phone connections to A5/0, you would have to: 1) Have to both receive and transmit. 2) Have a stronger connection than any other nearby cell towers. 3) Have a backbone connection back into the network so that you can actually negotiate phone calls to users connected to other cell phone towers. 4) Have to be able to handle multiple simultaneous connections. Some MITM spoof cell towers only establish a connection for the person of interest, and all other devices in the area loses connection. A pretty tell tale sign of a rogue base station operating in an area. So in short it is much easier just to have the keys...

hurin 12y ago
That's what I assumed (but I wondered if there was some other advantage I was missing). Are not all the ciphers breakable post collection anyways? Is it fair to say that this is effectively for the purpose of blanket non-targeted surveillance? Where by having the keys in their possession it gives them a shortcut for bulk analysis and saving CPU time that would otherwise be spent breaking encryption. And a cpu-processing-savings advantage justified cyber-attacking a foreign civilian corporation?
- rkangel 12y ago
  With the keys, you can do data collection now, and cracking later. You can do mass interceptions and then decide which calls you want to look at.
  - hurin 12y ago
    >With the keys, you can do data collection now, and cracking later. Do the attacks on A5/1 require known plaintext? I was under the impression that they do not.
    - BuildTheRobots 12y ago
      My understanding was that the A5/1 attack (and massive rainbow table) not only relies on known plaintext but also requires you to get the _start_ of the communication.