4 ms·

Isn't TPM just a honeypot of sorts? It seems strange to me that after successful open source encryption software, there was a shift to TPM, like you'll have a n

Isn't TPM just a honeypot of sorts? It seems strange to me that after successful open source encryption software, there was a shift to TPM, like you'll have a notion of super secure storage provided by big corporations and you should just not worry about it and not question. Surely there must be a backdoor access for three letter agencies to just download all the pins and passwords and then take a dip in the data, no worries.

jansommer 2y ago
Should be good enough for a personal tablet used for mail and browsing. If I drop it and someone curious finds it, I'd like to make it impossible for them to extract anything useful.
cheschire 2y ago
I prefer to think of TPM as equivalent to the chip in a smart card.
- mikepurvis 2y ago
  I think this is a good analogue. A smart card is a challenge-response system where sure you could extract the inner key, but doing so would take time and require destroying the card, which would alert the user— we all learned years ago about skimming and now the payment terminal comes to our table rather than the card being carried off elsewhere. TPM is one piece of a larger puzzle and provides a middle ground where among other things you can get full disk encryption without needing to input a memorized key on every boot.
eddythompson80 2y ago
I encourage you to read what a TPM is. A TPM isn't an "encryption" software/hardware. It's completely orthogonal to "successful open source encryption software". "successful open source encryption software" don't solve the main usability problem with encryption: "Where do I store my super secure 4096-bit private key so it's both secure and convenient to use"
- jeroenhd 2y ago
  I don't see why a TPM couldn't be open? Nobody makes open-source TPMs (because they're put inside CPUs or attached to motherboards with specific pins and protocols) but in theory you could just do it. All you need to do is make sure any secrets stored get wiped permanently whenever you flash new firmware. It'd be similar to secure boot: usable by default, but reconfigurable so that you can bring your own keys and signatures, putting you in complete control of your hardware, to the point where even the manufacturer no longer has a say in what's running and what isn't.
  - eddythompson80 2y ago
    You can make your own HSM using a raspberry pi pico https://www.picokeys.com/pico-hsm/ https://www.picokeys.com/pico-hsm/ > usable by default, but reconfigurable so that you can bring your own keys and signatures, putting you in complete control of your hardware, to the point where even the manufacturer no longer has a say in what's running and what isn't. You can control what's your TPM. That's how they work today. Sure their software isn't "open source" but there aren't that many 100% "open source hardware" options around. If you want to be able to flash it, build your own HSM. I don't know if there is a market for a prebuilt microcontroller with something like picokeys preinstalled. I know that the market for "open" hardware is tough.
  - raron 2y ago
    > I don't see why a TPM couldn't be open? Nobody makes open-source TPMs The main advantage of the TPM is how it is made physically. It should be designed to make it hard or impossible to read the secrets out of it and those things depends on how the components are manufactured on the silicon wafer. Maybe the manufacturing process could be published, but I don't think it would help much. You could probably write your own TPM emulator or modify swtpm a bit and compile it to any microcontroller, but in that case the chip could be easily decapped to make all the secrets readable.
    - varispeed 2y ago
      That's a definition of security by obscurity.
jeroenhd 2y ago
Maybe it's different for you, but I don't think any three letter agencies have some kind of TPM backdoor (they don't need to with how often TPM chips end up being vulnerable to common software exploits, the firmware being written in unsafe languages and all). If a government was going after me with enough force to use their TPM bypass trick, I'd probably be in jail for years on fake allegations regardless of encryption status. TPMs work great against things like common thieves and probably corporate espionage, if set up well. When implemented well, they provide no additional friction (except for having to store a recovery key somewhere) but all the security against a laptop being stolen at the airport you could wish for.
arghwhat 2y ago
It's not a honeypot, and it does have value when used properly. Their main purpose is to generate and store keys that cannot leave the device, instead performing signing operations as needed internally and only returning the result, and only if attestation passed. This is a lot better than just having private keys on disk. People just forget that security isn't absolute, and each solution has a threat model it is appropriate for. In case of full disk encryption, neither a TPM nor user input can protect against evil maid on its own for example - the TPM will unlock for anyone, while user input might be collected by a modified and malicious bootloader. Having both, however, works well. "TPM" is a bit dated as a term as it's all directly built into the processor nowadays, including for smartphones and such. Another modern feature in that catalogue is memory encryption, which rules out the attack described by OP as the rebooted machine would be unable to read old memory content.

jansommer 2y ago

Should be good enough for a personal tablet used for mail and browsing. If I drop it and someone curious finds it, I'd like to make it impossible for them to extract anything useful.

cheschire 2y ago

I prefer to think of TPM as equivalent to the chip in a smart card.

mikepurvis 2y ago
I think this is a good analogue. A smart card is a challenge-response system where sure you could extract the inner key, but doing so would take time and require destroying the card, which would alert the user— we all learned years ago about skimming and now the payment terminal comes to our table rather than the card being carried off elsewhere. TPM is one piece of a larger puzzle and provides a middle ground where among other things you can get full disk encryption without needing to input a memorized key on every boot.

eddythompson80 2y ago

I encourage you to read what a TPM is. A TPM isn't an "encryption" software/hardware. It's completely orthogonal to "successful open source encryption software". "successful open source encryption software" don't solve the main usability problem with encryption: "Where do I store my super secure 4096-bit private key so it's both secure and convenient to use"

jeroenhd 2y ago
I don't see why a TPM couldn't be open? Nobody makes open-source TPMs (because they're put inside CPUs or attached to motherboards with specific pins and protocols) but in theory you could just do it. All you need to do is make sure any secrets stored get wiped permanently whenever you flash new firmware. It'd be similar to secure boot: usable by default, but reconfigurable so that you can bring your own keys and signatures, putting you in complete control of your hardware, to the point where even the manufacturer no longer has a say in what's running and what isn't.
- eddythompson80 2y ago
  You can make your own HSM using a raspberry pi pico https://www.picokeys.com/pico-hsm/ https://www.picokeys.com/pico-hsm/ > usable by default, but reconfigurable so that you can bring your own keys and signatures, putting you in complete control of your hardware, to the point where even the manufacturer no longer has a say in what's running and what isn't. You can control what's your TPM. That's how they work today. Sure their software isn't "open source" but there aren't that many 100% "open source hardware" options around. If you want to be able to flash it, build your own HSM. I don't know if there is a market for a prebuilt microcontroller with something like picokeys preinstalled. I know that the market for "open" hardware is tough.
- raron 2y ago
  > I don't see why a TPM couldn't be open? Nobody makes open-source TPMs The main advantage of the TPM is how it is made physically. It should be designed to make it hard or impossible to read the secrets out of it and those things depends on how the components are manufactured on the silicon wafer. Maybe the manufacturing process could be published, but I don't think it would help much. You could probably write your own TPM emulator or modify swtpm a bit and compile it to any microcontroller, but in that case the chip could be easily decapped to make all the secrets readable.
  - varispeed 2y ago
    That's a definition of security by obscurity.

jeroenhd 2y ago

Maybe it's different for you, but I don't think any three letter agencies have some kind of TPM backdoor (they don't need to with how often TPM chips end up being vulnerable to common software exploits, the firmware being written in unsafe languages and all). If a government was going after me with enough force to use their TPM bypass trick, I'd probably be in jail for years on fake allegations regardless of encryption status. TPMs work great against things like common thieves and probably corporate espionage, if set up well. When implemented well, they provide no additional friction (except for having to store a recovery key somewhere) but all the security against a laptop being stolen at the airport you could wish for.

arghwhat 2y ago

It's not a honeypot, and it does have value when used properly. Their main purpose is to generate and store keys that cannot leave the device, instead performing signing operations as needed internally and only returning the result, and only if attestation passed. This is a lot better than just having private keys on disk. People just forget that security isn't absolute, and each solution has a threat model it is appropriate for. In case of full disk encryption, neither a TPM nor user input can protect against evil maid on its own for example - the TPM will unlock for anyone, while user input might be collected by a modified and malicious bootloader. Having both, however, works well. "TPM" is a bit dated as a term as it's all directly built into the processor nowadays, including for smartphones and such. Another modern feature in that catalogue is memory encryption, which rules out the attack described by OP as the rebooted machine would be unable to read old memory content.