4 ms·

I was wondering why Signal suggests a 6 digits passphrase by default. Even with a good key derivation algorithm, it’s trivial to brute force in a very short tim

I was wondering why Signal suggests a 6 digits passphrase by default. Even with a good key derivation algorithm, it’s trivial to brute force in a very short time.

jjtheblunt 5y ago
"trivial" means exactly what? I ask because it's not trivial to clone the memory of a phone and have a network of simulators capable of simultaneously enumerating each combination, to stave off slowed-next-attempt policies etc.
- tiagod 5y ago
  It's trivial as long as there are companies selling one-click solutions to do it.
- White_Wolf 5y ago
  If your budget is in the upper upper 5 digits range, it's trivial. If a serious attacker is set on getting your stuff, it's just a matter of time and money. It's down to how much the data is worth for the attacker.
- speedgoose 5y ago
  The brute force is trivial once you got the data, no pass phrase would be as secure. I think in this case a for loop on a single laptop would be fast enough.
  - jjtheblunt 5y ago
    but the os builds insert an increasing delay before allowing a next attempt. like the first iteration of the for loop runs at time 0, fails; second iteration gets to start 10 seconds later, fails; third iteration gets to start 1 minute later, fails; fourth iteration gets to start 1 hour later, fails; and so on.
    - speedgoose 5y ago
      But this doesn’t matter if you extract the data from the phone first.
      - jjtheblunt 5y ago
        right, but having done this in a previous role, over a decade ago, for legit non state level reasons, it requires custom hardware to even start the conversation.
upofadown 5y ago
That's for the phone itself, isn't it? So there would have to be some sort of hardware enclave involved that would rate limit guessing. Signal has no end point security past the phone so they would want the phone security to be as good a possible.
- C4K3 5y ago
  It is not just for the phone, the passphrase you set is also used to encrypt your data on the signal servers. Signal claims to use intel SGX to secure the passphrase on their servers, though.

I was wondering why Signal suggests a 6 digits passphrase by default. Even with a good key derivation algorithm, it’s trivial to brute force in a very short time.

jjtheblunt 5y ago

"trivial" means exactly what? I ask because it's not trivial to clone the memory of a phone and have a network of simulators capable of simultaneously enumerating each combination, to stave off slowed-next-attempt policies etc.

tiagod 5y ago
It's trivial as long as there are companies selling one-click solutions to do it.
White_Wolf 5y ago
If your budget is in the upper upper 5 digits range, it's trivial. If a serious attacker is set on getting your stuff, it's just a matter of time and money. It's down to how much the data is worth for the attacker.
speedgoose 5y ago
The brute force is trivial once you got the data, no pass phrase would be as secure. I think in this case a for loop on a single laptop would be fast enough.
- jjtheblunt 5y ago
  but the os builds insert an increasing delay before allowing a next attempt. like the first iteration of the for loop runs at time 0, fails; second iteration gets to start 10 seconds later, fails; third iteration gets to start 1 minute later, fails; fourth iteration gets to start 1 hour later, fails; and so on.
  - speedgoose 5y ago
    But this doesn’t matter if you extract the data from the phone first.
    - jjtheblunt 5y ago
      right, but having done this in a previous role, over a decade ago, for legit non state level reasons, it requires custom hardware to even start the conversation.

upofadown 5y ago

That's for the phone itself, isn't it? So there would have to be some sort of hardware enclave involved that would rate limit guessing. Signal has no end point security past the phone so they would want the phone security to be as good a possible.

C4K3 5y ago
It is not just for the phone, the passphrase you set is also used to encrypt your data on the signal servers. Signal claims to use intel SGX to secure the passphrase on their servers, though.