Support secure hardware authentication on Mac.

[LoganDark]

Since 2021, all models of Mac have supported Touch ID. Touch ID can be used to authenticate access to encrypted Keychain data, providing stronger hardware-level protection than a simple PIN. I refuse to use an app that thinks a PIN is secure; a 6-digit PIN can be brute forced offline in under a second. Even if a PIN were secure, I refuse to use an app that forces me to set one, because there is far more secure hardware available that you should be using.

[jgriffiths]

Commenting here because I don't want casual readers to misunderstand the Green security model.

a 6-digit PIN can be brute forced offline in under a second.

The PIN in Green is used to fetch an AES encryption key from a remote blind PIN server, which may also be self-hosted. If 3 invalid PINs are given, the remote server permanently and irrevocably destroys the encryption key. So this cannot be brute forced.

In order to be in a position to actually brute force a Green PIN offline, an attacker would need to compromise your local storage to fetch the encrypted data, and then compromise the Green PIN server (or your private instance of it) to exfiltrate all the blind stored data and then apply each in turn to the local data in order to attempt to recreate the mnemonic seed.

It would be far more practical for an attacker targeting a software wallet to get root and read the mnemonic/seed from the wallet process memory. Storing the encryption key in any kind of enclave in the host foes not protect from this.

We advise that users use a hardware wallet like Jade to ensure that the signing key(s) are not present on the wallet device at all, if they are holding any significant value in the wallet.

there is far more secure hardware available that you should be using

Yes, use a hardware wallet that performs the signing offline so that the signing keys are not on the wallet device.

[LoganDark]

I find it weird that a non-custodial wallet would require a remote server to be placed in control of your access. (I know a few that have optional 2FA through such a mechanism, but requiring it is just total bogus.) A truly blind server wouldn't know anything about what it's unlocking, but that's still practically security theater (and a huge point of failure, no less) on macOS where a Secure Enclave with biometrics exists.

It's also worth noting that none of the semantics you described seem to be documented anywhere.

Yes, use a hardware wallet that performs the signing offline so that the signing keys are not on the wallet device.

There are levels of security between trusting a remote server to help you decrypt your key and purchasing a dedicated external HSM for each key. Notably, the Secure Enclave is an HSM built into every Apple Silicon device, and yet seems entirely neglected here "because you should be using our cold wallet instead".

Apple devices can be just as secure as any cold wallet when operated correctly, because the Secure Enclave can act exactly as that hardware wallet:

1. The Secure Enclave can generate keys offline without the main CPU ever seeing them.
2. The Secure Enclave can guard those keys behind biometric authentication or the device passcode, without your app ever having to handle authentication (let alone remotely).
3. The Secure Enclave can ensure that only properly signed, trusted and untampered versions of your app can perform any operations with the key.

The only downside is that because you can never see the key, it can never leave that Secure Enclave, so you never get a recovery phrase or the ability to move between devices. Technically that makes it more secure than a cold wallet that can be plugged into any device, but what do I know. (Note that 'security' quickly diverges from ensuring your own access to your funds, towards ensuring no unauthorized access to your funds.) You could also use the Secure Enclave only to hold that decryption key, rather than a remote server, which would retain the ability to manipulate Bitcoin key material in application memory.

[jgriffiths]

You have mostly missed my point. Unless the enclave supports all of the operations of a bitcoin/liquid hardware wallet (it doesn't), then the master key must be given to/decrypted by the app, at which point it is resident in memory and a significantly easier target than the remote PIN server. Your assertion that the PIN is trivially brute forceable is incorrect, hardware wallets and offline signing are supported, and multisig further has 2fa protection for spending even if someone gains access to your mnemonics.

I find it weird that a non-custodial wallet would require a remote server

I'm not up on the latest UX for the wallets, the underlying code (that I work on) does not require a PIN for software wallets- if you want to enter your mnemonics each time you login that works. If that is not exposed in the wallets feel free to raise an issue to add it. You can also create a watch only wallet and export PSBT files to sign completely offline.

You have made your feature request, locking the conversation. I'll make sure its passed on to the wallet developers.