I mentioned the Trezor earlier particularly Model T where passphrase and recovery seed can be entered on it directly. It has a different model than a typical HSM since it doesn't store anything other than the seed which is combined with entered passphrases to derive wallets/keys.
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It doesn't include any proprietary software and the whole thing is an open design that other people are able to build (and have successfully done so in practice). The primary purpose is for cryptocurrency wallets but it works well for U2F, GPG, SSH and various other purposes too.
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There are definitely options beyond proprietary ones, including options with much different approaches than a traditional HSM storing the keys with / without encryption (ideally with a passphrase entered onto the device). I really like the approach pioneered for Bitcoin wallets.
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Since that lets you generate keys on the hardware wallet, back up the high entropy recovery seed as a phrase, verify you backed it up correctly and then if you need to recover on a new device you can enter it directly onto a new hardware wallet without exposing it to a computer.
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The traditional approach is good if you have existing SSH and GPG keys that need to be moved onto an HSM. I'll definitely prefer the deterministic wallet approach for new keys though. It's not that bad to migrate to new SSH keys but GPG tends to make rotating keys very painful.
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Signing keys for firmware usually can't be rotated at all since they're burned into fuses so that's another case where a more traditional HSM is the best option since existing keys need to be migrated. Android app signing keys were similar, but they've finally added key rotation.
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I really like the - code has been audited by so that is a huge plus in my book, and there's tons of eyes on the code as maintainers use them as well. Nothing against - they are an incredible company and I use their devices for btc
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Entering a password on device (like you mention) is a big plus for Trezor though, as is their open CPU. (What smart card does nitrokey use?)
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I find the recovery model to be the biggest advantage of the approach based on deterministic wallet design. The hardware wallet generates a high entropy seed, displays it as a recovery phrase and you can write it down, store it and recover without exposing it to the computer.
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It's the approach to the security model including recovery, passphrases and on-device input / confirmations that I like rather than the hardware though. I don't want to import keys generated on my computer or expose them to it from cold storage if I need to do recovery, etc.
The Trezor hardware isn't what's compelling about it. It's just a standard embedded computer with secure boot and a tamper evident case. I'd like to see more implementations that are fully compatible with not just the cryptocurrency wallet aspect but also SSH, GPG, U2F, etc.
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I think they have by far the best approach to this on the Trezor Model T and I'd really like to see alternate implementations with different trade-offs like having a secure element for storing the seed and doing cryptographic operations at the expense of openness and flexibility.
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Ah, I misunderstood what you meant. I'm successfully using their current SSH support already and I plan on using their GPG support to replace my existing aging key which has been exposed to multiple generations of laptops and workstations. GPG makes key rotation horrible though.
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Hopefully we get a world where we have the combination of all the above/ideal package - but right now, I think the most secure is hardware/most eyes on audited code