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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 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.
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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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Ideally, there would be a much more tamper resistant general purpose SoC available so it wouldn't need to be a compromise. They do have basic tamper resistance already but it would be good to have lower-level support from the SoC like memory encrypted with a hardware key, etc.
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