It is never recommended to buy a used hardware wallet because the other person who had this in use before selling it to you may have flashed the firmware or do some other nasty trick. This way even if you wipe your wallet that firmware installed there on the chip may have bugs and it may show your seed to the person who had this before. This happens very rarely but just to be sure because I suppose in a hardware wallet you will keep a good amount of bitcoin.
That wouldn't be possible. Both Trezor and Ledger have security measures to avoid the attempt of installing malwares in your hardware wallet. See above:
Trezor:Reflashing the TREZOR with evil firmware
Official TREZOR firmware is signed by the SatoshiLabs master key. Installing unofficial firmware on the TREZOR is possible, but doing so will wipe the device storage and TREZOR will show a warning every time it starts. Reprogramming the bootloader is impossible because all TREZORs ship with their secure programming fuse blown.
Inspect the TREZORs memory with an electron microscope
You might imagine yourself dissolving the TREZOR CPU in acid, finding the reprogramming fuse, repairing it, and then loading evil firmware on the TREZOR. I’m no science fiction author, but my guess is – this might be possible. However, the Cortex M3 is a sensitive multilayer chip. The components inside are much smaller than those fake eBay amps. Chances are, all you’d end up doing is destroying the chip. Even if you succeeded in doing so, this will be a costly and time-consuming task. In the end, the bitcoins will be gone already because the original owner will have changed their recovery seed upon discovering that their TREZOR was stolen.
Evil maid attack - replace the TREZOR with a fake
It might be possible for an evil ninja, or your little brother, to steal your TREZOR and replace it with a fake TREZOR. If the fake TREZOR was embedded with a wireless transmitter, then the fake TREZOR could wirelessly transmit any PIN it received. The attacker would then have full access to your funds.
If you are concerned about such an attack, it is a good idea to sign the back of your TREZOR with a permanent pen. Don’t forget to check the signature before each use.
The TREZOR’s chassis is sealed using ultrasound. Opening the TREZOR without destroying the case is nearly impossible.
Ledger: How to verify the security integrity of my Nano S?On the hardware side, if you want to check that the Nano S has not been tampered with, or the applications running are the official apps, here are a few things that you might need to know:
1) The Secure Element checks the full microcontroller flash at boot (this is described in our blog post). If it has been modified, you'll get a warning at boot. As an additional check, you can open the device to verify that no additional chip has been added (referring to the attached picture) and that the MCU is an stm2f042k6 (with 32 Kb flash, as a bigger flash could contain code fooling the Secure Element validation). Markings on the chip can vary but you should see the string "042K6".
2) The Secure Element itself is personalized at factory with an attestation proving that it has been created by us. You can verify it by running
pip install --no-cache-dir ledgerblue
python -m ledgerblue.checkGenuine --targetId 0x31100002
The source code is available here:
https://github.com/LedgerHQ/blue-loader-python/blob/master/ledgerblue/checkGenuine.py3) Each individual application will display a "Non Genuine" warning if not signed when opened. A modified User Interface (as found in
https://github.com/LedgerHQ/nanos-ui) will also display a warning message on boot.
4) The root of trust for the current batch is the following secp256k1 public key : 0490f5c9d15a0134bb019d2afd0bf297149738459706e7ac5be4abc350a1f818057224fce12ec9a
65de18ec34d6e8c24db927835ea1692b14c32e9836a75dad609 - as checked in checkGenuine.py
https://github.com/LedgerHQ/blue-loader-python/blob/master/ledgerblue/checkGenuine.py#L72 Sources:
https://doc.satoshilabs.com/trezor-faq/threats.htmlhttp://support.ledgerwallet.com/knowledge_base/topics/how-to-verify-the-security-integrity-of-my-nano-s
