[varispeed]

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.

[arghwhat]

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.

[eddythompson80]

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]

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]

You can make your own HSM using a raspberry pi pico 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.

[tremon]

An open TPM does exist: https://www.qemu.org/docs/master/specs/tpm.html#the-qemu-tpm...

The TPM emulation offers a full TPM implementation in software, for providing TPM functionality to a virtual machine when the host doesn't have one (or, when the TPM needs to be virtualized for other reasons, e.g. migration).

[raron]

> 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]

That's a definition of security by obscurity.

[PhilipRoman]

Unlike with cryptography, there is no rigorous notion of physical security. Doors, locks and even security systems can all be overcome with sufficient effort, skill and resources. They work because physical attacks require proximity and are very hard to keep anonymous. I seriously doubt that any TPM implementation would last a week against government funded researchers with state of the art technology, but that doesn't mean the TPM is useless.

[varispeed]

No, it's the same. Cryptography is like a lock that you can overcome with mathematical force. It's just in different domain than physical objects.

If you know how the lock is built, you can rule out existence of master key for instance. You don't know if your TPM chip has API where three letter agency can just download the keys from it. You are in the dark.

Same with cryptography, you can choose the method, just like you can choose type of lock. There are locks that have not yet been picked, but you can use a hammer, similar with cryptography - you can use quantum computer etc.

[raron]

Some of these features makes it harder to (physically) probe the internal parts of the chip and read out secret values:

https://en.wikipedia.org/wiki/Secure_cryptoprocessor#Feature...

These things make it harder to break into the internals of the chip regardless of they being kept secret, so I wouldn't call it security by obscurity. I'm not even sure you can apply that principle to physical security.

[rcxdude]

No, it's security by intrusion detection, generally. HSMs are designed to be boxes that it's very hard to get a secret out of with physical access. TPMs generally aren't the most paranoid version, but it gets more expensive and less practical as you go further (e.g. a large box which has a battery backup, keeps the secrets in RAM, and will wipe them as soon at it detects any funny business. These are DIYable, but the list of tricks by attackers is long and it's hard to cover all of them at once). A TPM is generally somewhere in between that and a regular micro with no particular effort to prevent readout of internal storage, in that they are small, can persist secrets without power, but are still difficult to attack physically (~maybe at the level of advanced criminal organisations, ~probably at state level if they're willing to spend some money on it, even absent a backdoor).

[okanat]

Printing out your 2FA recovery keys and storing them in a safe also is.

[eptcyka]

Is a yubikey then employing security by obscurity?

[formerly_proven]

100%

They’re built from essentially the same secure MCUs as traditional TPMs and both the hardware and the proprietary crypto libraries used on them have been exploited many times over.

[yx827ha]

It's in the works. https://opentitan.org/

[adrian_b]

You can store it encrypted with a password on a USB memory that you insert when booting the computer, like you would use a key for starting a car.

This is what I actually do. I also store the OS kernel on the USB memory and I boot from there, with the root file system set to mount an internal SSD. The SSDs in the computer are completely encrypted with such long "super secure" keys (distinct for each SSD and selected automatically based on their serial number), and they do not store any information about the keys.

I have used this system for years and I find it very convenient. My computers cannot be booted without inserting the bootable USB memory and also giving the correct password. I have multiple bootable keys stored in different places, for the case when one becomes defective or lost.

[varispeed]

I am sorry I wasn't clear. I am aware that TPM is a key storage. Just I am not convinced they keys it stores are secure. It smells of security by obscurity and all big corporations are happy clappy to use it and government is silent about it, which likely means they have a backdoor.

[gruez]

>It smells of security by obscurity and all big corporations are happy clappy to use it and government is silent about it, which likely means they have a backdoor.

The government is also pretty silent about AES. Does it mean that's backdoored as well? More to the point, I'm not sure what the proposed alternative is. Not using TPM, and exposing yourself to bootkits and evil maid attacks?

[prmoustache]

It is security the same way a lock is. It limits low efforts attempt which is why we put locks in our doors and close our most easily accessible windows in the first place.

[p_ing]

Lest one forget NSAKey! /s

This type of /r/ufos|/r/aliens speculation isn't particularly useful. It comes with no evidence of TPMs being backdoor'ed. Have they been compromised [at least pre-2.0]? Yes, in as much as Apple's Secure Enclave has as an example.

Gut feelings aren't always correct and for topics which have a sort of 'correctness' about them, they're not useful.

Otherwise we're debating to prove a negative.

[jeroenhd]

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.

[jansommer]

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]

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

[mikepurvis]

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.