4 ms·

Why not just use a USB drive if your threat model doesn't involve physical access to the device?

ChrisClark 8y ago
Because a USB drive is less secure for this use case. If you stick a USB drive into a compromised computer to make a transaction, a virus can steal the private key. If you stick a Trezor or Ledger into a compromised computer to make a transaction, your private key is still safe.
mcpherrinm 8y ago
Malware on the host PC can steal your private key. An attacker who gets brief physical access (eg, you look away for a minute) can quickly copy a USB drive. While this attack shows the trezor is probably a bit amateur-hour, it does provide some amount of value.
- exoesquitur 8y ago
  That's not how it works. The trezor is not a USB storage device, it is a usb serial port that communicates with an MCU.
  - paulhilbert 8y ago
    No one claimed it is...
  - mcpherrinm 8y ago
    I can see how reading my comment in isolation would be confusing. Specifically, I was answering the question "Why not just use a USB drive"
sturmeh 8y ago
Because any process with i/o capability on the host OS can read the private key on the USB? Short of a oscilloscope hiding in the computer you use (totally possible), no process can derive the private key from the Trezor in theory. Even if you have processes that blatantly copy every USB's contents (or even log all interactions verbosely) and log all key presses/clipboard interactions on the machine, you can still use a Trezor without compromising anything. You can also verify that your clipboard is not being manipulated as the Trezor can verify the address it will be signing a transaction with on the display.
- DoctorOetker 8y ago
  the oscilloscope has 20 MHz bandwith, any old VGA monitor (CRT/LCD/etc) has at least 3 30MHz ADCs (1024x768x60=~60Msps=~30MHz bandwidth). ADC's may be expensive in low volume discrete form, but integrated in (standardized!) peripheral bus (USB) controllers, this could be very cheap. As always, it depends on the threat model: do you wish to protect against manufacturers/nation states or not?
  - fapjacks 8y ago
    I would love to read a more thorough explanation of what you're suggesting.
    - dsyko 8y ago
      I believe they are suggesting that the above comment "Short of a oscilloscope hiding in the computer you use" might not be so far fetched. The hardware needed to do the type of analysis used for this attack has been around a long time and is presumably very cheap at scale. So if for example a nation/company that has control over the manufacture of a large number of USB controllers decided they wanted to be able to do this kind of power analysis on all USB devices plugged into their controllers they could do so easily. Esentially adding a micro controller with an Analog to Digital converter that can watch the power pin inside the USB controller/port itself would be relatively simple and cheap.
  - esmi 8y ago
    Although they don’t have 20MHz of bandwidth and the necessary sample rate there are USB3 power delivery controllers on the market today which do exactly that. Some even embed the microcontroller too.

Because a USB drive is less secure for this use case. If you stick a USB drive into a compromised computer to make a transaction, a virus can steal the private key. If you stick a Trezor or Ledger into a compromised computer to make a transaction, your private key is still safe.

mcpherrinm 8y ago

Malware on the host PC can steal your private key. An attacker who gets brief physical access (eg, you look away for a minute) can quickly copy a USB drive. While this attack shows the trezor is probably a bit amateur-hour, it does provide some amount of value.

exoesquitur 8y ago
That's not how it works. The trezor is not a USB storage device, it is a usb serial port that communicates with an MCU.
- paulhilbert 8y ago
  No one claimed it is...
- mcpherrinm 8y ago
  I can see how reading my comment in isolation would be confusing. Specifically, I was answering the question "Why not just use a USB drive"

sturmeh 8y ago

Because any process with i/o capability on the host OS can read the private key on the USB? Short of a oscilloscope hiding in the computer you use (totally possible), no process can derive the private key from the Trezor in theory. Even if you have processes that blatantly copy every USB's contents (or even log all interactions verbosely) and log all key presses/clipboard interactions on the machine, you can still use a Trezor without compromising anything. You can also verify that your clipboard is not being manipulated as the Trezor can verify the address it will be signing a transaction with on the display.

DoctorOetker 8y ago
the oscilloscope has 20 MHz bandwith, any old VGA monitor (CRT/LCD/etc) has at least 3 30MHz ADCs (1024x768x60=~60Msps=~30MHz bandwidth). ADC's may be expensive in low volume discrete form, but integrated in (standardized!) peripheral bus (USB) controllers, this could be very cheap. As always, it depends on the threat model: do you wish to protect against manufacturers/nation states or not?
- fapjacks 8y ago
  I would love to read a more thorough explanation of what you're suggesting.
  - dsyko 8y ago
    I believe they are suggesting that the above comment "Short of a oscilloscope hiding in the computer you use" might not be so far fetched. The hardware needed to do the type of analysis used for this attack has been around a long time and is presumably very cheap at scale. So if for example a nation/company that has control over the manufacture of a large number of USB controllers decided they wanted to be able to do this kind of power analysis on all USB devices plugged into their controllers they could do so easily. Esentially adding a micro controller with an Analog to Digital converter that can watch the power pin inside the USB controller/port itself would be relatively simple and cheap.
- esmi 8y ago
  Although they don’t have 20MHz of bandwidth and the necessary sample rate there are USB3 power delivery controllers on the market today which do exactly that. Some even embed the microcontroller too.