4 ms·

We're talking about exactly the same threat. What I'm pointing out is that state adversaries won't have to "notice" this; all they'll have to do is plug the dev

by tptacek 3mo ago

We're talking about exactly the same threat. What I'm pointing out is that state adversaries won't have to "notice" this; all they'll have to do is plug the device into a standard commercial forensics scanner product --- and we're stipulating that they're plugging the device in already (else what does it matter what bits are on it). They pay other people to notice this stuff for them!

awesome_dude 3mo ago
> They pay other people to notice this stuff for them! Money, even at state level, is not some infinite resource (and neither is time). States put effort into what they consider worth investigating - no state strip searches every incoming traveller, and goes through every item in their possession - it's possible for them to do, and if they did they'd find a hang of a lot more contraband, but it's costly, time consuming, and politically risky.
- mediaman 3mo ago
  He's saying they just plug your USB stick into some gizmo sold to the state, and it's going to find enough to escalate it. If the idea is that there's no point in encrypting anything on a USB stick, and you just hope they don't look at it at all, sure. But there is no threat model here that includes "check the USB stick" and does not automatically lead to finding and breaking "hidden" content.
  - NetMageSCW 3mo ago
    Try to explain how the hidden content would be found? It effectively doesn’t exist until the password is in place. It isn’t hidden, it isn’t connected at all.
    - mingus88 3mo ago
      I’m no expert but I can imagine a scenario where an x-ray scan can notice an SD card embedded into the controller and flag that for follow-up SD card the author says was added to offset the cost of eMMC but would presumably stand out as anomalous with whatever AI is classifying the scan
      - marysol5 3mo ago
        Yeah the SD card is going to be glaring for anybody with actual investigation into this device. But saying that, the sheer amount of fake flash storage out there now, that's just a glorified USB-SD reader in a box.
      - awesome_dude 3mo ago
        I mean - if there are multiple sdcards in the device - and they each contain a hidden partition - how is the X-RAY going to determine that the reported 5GB (or whatever) isn't matching the devices actual 7GB (for example)
    - deleted 3mo ago
      [deleted]
whizzter 3mo ago
I think part of the entire design is that it's quite hard to detect. 1: Reads/Writes are just routed to a COTS SD-card. 2: Unless the (correct?) password is detected in the write-data that starts the disconnect procedure. The only way to detect it from what I can see is to profile writes then append a "password:" string multiple times to measure the write-delay, only works if the CPU cost is large enough to overtake the SD-card measurably and some constant-time optimizations should make it more or less undetectable. It's a clever design and I think it should be possible to optimize to become more or less unrecognizable.
- tptacek 3mo ago
  Can you flesh that out? If I've missed something and oversimplified the design here, I'd want to clarify that!
  - whizzter 3mo ago
    The encryption/hiding is done by the firmware, hence.. 1: The drive more or less looks like any boring old usb-stick, it isn't even uncommon for cheap fake Amazon sellers to sell sticks with SD-card's as faked large drives (so even with X-ray inspection it doesn't look too much out of order). 2: To a computer, since the firmware presents a regular UMASS device, there isn't anything telling the computers over-the-wire protocol that anything is amiss (since the real size is hidden by the firmware and regular accessible blocks just behave normally). So, short of an intrusive teardown of the device to read the true size of the SD-card and even knowing the presence of a hidden volume, the only over the wire that can help discerning this from a regular drive is timing attacks (And as you notice from this thread, people are jumping on to suggest solutions to minimize or even remove that).
- 05 3mo ago
  > The only way to detect it from what I can see is to profile writes then append a "password:" string multiple times to measure the write-delay, - Have the first check be a simple 8bit hash that filters out most passwords in microseconds, or use a customizable prefix instead of “password:”. - have your password checking thread run in background at idle priority - when you get an async password match, force usb disconnect and reconnect and the system will rescan the bus and mount your real drive. Short of adversary dumping drive firmware (or them figuring out your hn account t, having a LLM scan the messages and finding this conversation) it’s not really easily detectable..

by tptacek 3mo ago

awesome_dude 3mo ago

> They pay other people to notice this stuff for them! Money, even at state level, is not some infinite resource (and neither is time). States put effort into what they consider worth investigating - no state strip searches every incoming traveller, and goes through every item in their possession - it's possible for them to do, and if they did they'd find a hang of a lot more contraband, but it's costly, time consuming, and politically risky.

mediaman 3mo ago
He's saying they just plug your USB stick into some gizmo sold to the state, and it's going to find enough to escalate it. If the idea is that there's no point in encrypting anything on a USB stick, and you just hope they don't look at it at all, sure. But there is no threat model here that includes "check the USB stick" and does not automatically lead to finding and breaking "hidden" content.
- NetMageSCW 3mo ago
  Try to explain how the hidden content would be found? It effectively doesn’t exist until the password is in place. It isn’t hidden, it isn’t connected at all.
  - mingus88 3mo ago
    I’m no expert but I can imagine a scenario where an x-ray scan can notice an SD card embedded into the controller and flag that for follow-up SD card the author says was added to offset the cost of eMMC but would presumably stand out as anomalous with whatever AI is classifying the scan
    - marysol5 3mo ago
      Yeah the SD card is going to be glaring for anybody with actual investigation into this device. But saying that, the sheer amount of fake flash storage out there now, that's just a glorified USB-SD reader in a box.
    - awesome_dude 3mo ago
      I mean - if there are multiple sdcards in the device - and they each contain a hidden partition - how is the X-RAY going to determine that the reported 5GB (or whatever) isn't matching the devices actual 7GB (for example)
  - deleted 3mo ago
    [deleted]

whizzter 3mo ago

I think part of the entire design is that it's quite hard to detect. 1: Reads/Writes are just routed to a COTS SD-card. 2: Unless the (correct?) password is detected in the write-data that starts the disconnect procedure. The only way to detect it from what I can see is to profile writes then append a "password:" string multiple times to measure the write-delay, only works if the CPU cost is large enough to overtake the SD-card measurably and some constant-time optimizations should make it more or less undetectable. It's a clever design and I think it should be possible to optimize to become more or less unrecognizable.

tptacek 3mo ago
Can you flesh that out? If I've missed something and oversimplified the design here, I'd want to clarify that!
- whizzter 3mo ago
  The encryption/hiding is done by the firmware, hence.. 1: The drive more or less looks like any boring old usb-stick, it isn't even uncommon for cheap fake Amazon sellers to sell sticks with SD-card's as faked large drives (so even with X-ray inspection it doesn't look too much out of order). 2: To a computer, since the firmware presents a regular UMASS device, there isn't anything telling the computers over-the-wire protocol that anything is amiss (since the real size is hidden by the firmware and regular accessible blocks just behave normally). So, short of an intrusive teardown of the device to read the true size of the SD-card and even knowing the presence of a hidden volume, the only over the wire that can help discerning this from a regular drive is timing attacks (And as you notice from this thread, people are jumping on to suggest solutions to minimize or even remove that).
05 3mo ago
> The only way to detect it from what I can see is to profile writes then append a "password:" string multiple times to measure the write-delay, - Have the first check be a simple 8bit hash that filters out most passwords in microseconds, or use a customizable prefix instead of “password:”. - have your password checking thread run in background at idle priority - when you get an async password match, force usb disconnect and reconnect and the system will rescan the bus and mount your real drive. Short of adversary dumping drive firmware (or them figuring out your hn account t, having a LLM scan the messages and finding this conversation) it’s not really easily detectable..