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Comment by thomashabets2 | Hacker News Reader

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thomashabets2

> TPMs are soldered onto motherboards so they are not portable. Like U2F, they also don’t let you sign arbitrary data.

Incorrect!

You can use TPM chips to RSA sign arbitrary data, and use that to authenticate SSH:

https://blog.habets.se/2013/11/How-TPM-protected-SSH-keys-wo...

Even under Windows: https://blog.habets.se/2016/10/Windows-SSH-client-with-TPM.h...

The secret is using TSS_HASH_OTHER as the hash algorithm, which tells the TPM "it's already hashed". Whether it actually is hashed, or just raw input, is up to you.

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Also on a modern Apple device, you can use the Secure Enclave AES Engine to perform encryption and decryption. You can also use the Public Key Accelerator (PKA) for RSA and ECC (Elliptic Curve Cryptography) signing and encryption algorithms with hardware keys that stay within the PKA. https://support.apple.com/en-ca/guide/security/sec59b0b31ff/... covers an overview of the technologies involved. Of particular interest is probably the "Secure Enclave feature summary" at the bottom of that page which lists which Apple chips support which features.

Also relevant: https://developer.apple.com/documentation/security/certifica... and CryptoKit https://developer.apple.com/news/?id=3bwfq45y and https://developer.apple.com/documentation/cryptokit (Note that the Linux version of CryptoKit doesn't get any of the fancy hardware features, you'll need an Apple OS for them.)

TPMs are also sold separately that which can be plugged in to motherboards, e.g. Gigabyte (https://www.gigabyte.com/us/Motherboard/GC-TPM20-SPI-20) and Asus (https://www.asus.com/Motherboards-Components/Motherboards/Ac...) to name a couple.

The article has a couple of other weird faults, too:

1. I'm not sure why the author is complaining about FIDO2 having backwards compatibility with U2F/CTAP1. The article even incorrectly claims FIDO2 is "a 3rd incompatible standard" only to counter-argue the point a few paragraphs below explaining CTAP? People not having to throw away their perfectly fine old devices is a good thing in my book.

2. "All FIDO standards are web-centric and aren’t designed with any other client software in mind" the first part is true, the second part not so much. For example FIDO2 supports silent authentication (no user interaction) while WebAuthn explicitly does not[0]. It also supports the hmac-secret extension[1] which is used for offline authentication with Azure Active Directory[2] and IIRC no WebAuthn browser implementation exposes this extension to web apps.

[0]: see e.g. discussion on https://github.com/w3c/webauthn/issues/199

[1]: https://fidoalliance.org/specs/fido-v2.1-rd-20210309/#sctn-h...

[2]: https://docs.microsoft.com/en-us/azure/active-directory/auth...

I also don't know why the author thinks HSMs cost "hundreds to tens of thousands of dollars". In the first place, TPMs are a subcategory of HSMs and don't cost that much. In the second place, HSMs like the Microchip ATECC608B cost <$1 for the bare board.

OP says devices, so I read rack-mount gear that you buy when you can't use (or trust) AWS KMS, not chips.

I implemented a firmware signing infrastructure for a large embedded hardware manufacturer using USB Nitrokey HSM devices (sub-$100/ea). We got the functionality we wanted from them at a fraction of the price point of the "big name" HSM manufacturers' offerings. The development effort to integrate the Nitrokey HSM, as a simple PKCS#11 device, was very simple. What we could get of the big-name HSM manufacturers' development docs, w/o an NDA or a purchase, looked to be much more difficult to integrate.

Well, I don't know if they really meant rack-mount gear, but sure it costs a little extra to get it usable with a general-purpose computer.

Specifically, you can get that Microchip HSM in a form factor that plugs into a click shield, then plug the click shield into a Raspberry Pi's GPIO pins. You now have a PKCS#11-usable HSM from a Pi. Including the click shield still puts the cost at <$20.

(I have a few such setups lying around because my $dayjob includes a PKCS#11-consuming application that runs on such setups.)

Not yet implemented, but Solo 2 has a "stretch goal" to provide HSM functionality, if that would be good enough. https://www.indiegogo.com/projects/solo-v2-safety-net-agains...

Even then, you can buy a Yubico YubiHSM device for 650€.

Well, that is hundreds of dollars, isn't it? :)

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