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Native Secure Enclave backed SSH keys on macOS

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Re: Native Secure Enclave backed SSH keys on macOS

#31

Post by cedws »

jedberg wrote: post #13

If I understand correctly, this means you can't back up the private key, correct? It's in the Secure Enclave, so if you lose your laptop, you also lose the key? Since it looks like export only really exports the public key not the private one? Probably not the worst thing, you most likely have another way to get into the remote machine, or an admin who can reset you, but still feels like a hole. Or am I missing somet…

You're not really supposed to 'export' keys. Any time you move a key you risk exposing it. The idea of PKI is that only public keys move, the private key stays in one place, ideally never seen.

Re: Native Secure Enclave backed SSH keys on macOS

#32

Post by nothrabannosir »

comprev wrote: post #17
jedberg wrote: post #13

If I understand correctly, this means you can't back up the private key, correct? It's in the Secure Enclave, so if you lose your laptop, you also lose the key? Since it looks like export only really exports the public key not the private one? Probably not the worst thing, you most likely have another way to get into the remote machine, or an admin who can reset you, but still feels like a hole. Or am I missing somet…

Inability to export the private key is no different from using an YubiKey? You can't "backup" the private key they generate either.

Which makes yubikey impossible to use with geographically distributed backups. You need the backup available at all times for when you want to register with any new service.

This is why you should use a device which allows exporting the seed, like e.g. multi purpose hardware crypto wallets.

Re: Native Secure Enclave backed SSH keys on macOS

#33

Post by wahern »

Time to up my game and finish adding new features to KeyMux, which supports enclave keys for SSH, SSL, and PGP, including in mixed-use scenarios, such as secure enclave-backed SSL peer authentication to a Vault server for SSH authentication with a non-exportable Vault private key: https://keymux.com/ (https://apps.apple.com/us/app/keymux/id6448807557)

Re: Native Secure Enclave backed SSH keys on macOS

#34

Post by jedberg »

cedws wrote: post #31
jedberg wrote: post #13

If I understand correctly, this means you can't back up the private key, correct? It's in the Secure Enclave, so if you lose your laptop, you also lose the key? Since it looks like export only really exports the public key not the private one? Probably not the worst thing, you most likely have another way to get into the remote machine, or an admin who can reset you, but still feels like a hole. Or am I missing somet…

You're not really supposed to 'export' keys. Any time you move a key you risk exposing it. The idea of PKI is that only public keys move, the private key stays in one place, ideally never seen.

I've been in the security space for 25 years, and understand the theory of PKI. But I've also been in the ops space for 30 years, and understand that if you don't balance security theory with operational practice, critical business functions can fail.

Ideally yes, the private key is never seen. In reality, it needs to be backed up in a secure place so it can be restored in the event of a failure.

Re: Native Secure Enclave backed SSH keys on macOS

#35

Post by epistasis »

nothrabannosir wrote: post #32
comprev wrote: post #17

Earlier quoted context omitted.

Inability to export the private key is no different from using an YubiKey? You can't "backup" the private key they generate either.

Which makes yubikey impossible to use with geographically distributed backups. You need the backup available at all times for when you want to register with any new service. This is why you should use a device which allows exporting the seed, like e.g. multi purpose hardware crypto wallets.

Are you talking about SSH or a different setting?

With SSH, you can always share the primary and backup pub keys, even if you don't have the backup key handy.

Re: Native Secure Enclave backed SSH keys on macOS

#37

Post by asteroidburger »

cedws wrote: post #31
jedberg wrote: post #13

If I understand correctly, this means you can't back up the private key, correct? It's in the Secure Enclave, so if you lose your laptop, you also lose the key? Since it looks like export only really exports the public key not the private one? Probably not the worst thing, you most likely have another way to get into the remote machine, or an admin who can reset you, but still feels like a hole. Or am I missing somet…

You're not really supposed to 'export' keys. Any time you move a key you risk exposing it. The idea of PKI is that only public keys move, the private key stays in one place, ideally never seen.

It's much safer to export a key one time and import it into a new machine, or store it in a secure backup, than to keep it just hanging out on disk for eternity, and potentially get scooped up by whatever malware happens to run on your machine.

Re: Native Secure Enclave backed SSH keys on macOS

#38

Post by hylaride »

jedberg wrote: post #13

If I understand correctly, this means you can't back up the private key, correct? It's in the Secure Enclave, so if you lose your laptop, you also lose the key? Since it looks like export only really exports the public key not the private one? Probably not the worst thing, you most likely have another way to get into the remote machine, or an admin who can reset you, but still feels like a hole. Or am I missing somet…

Strictly speaking people should be using multiple keys so if a device is lost/stolen, you're not left high and dry. Ideally one per device, especially if they don't support some kind of secure enclave.

I keep one in a yubikey protected by a PIN that sits in a safety deposit box, too. This way if I have my laptop, phone, and day-to-day yubikey is a house that suddenly burns down, I'm still ok.

Re: Native Secure Enclave backed SSH keys on macOS

#39

Post by [deleted] »

jedberg wrote: post #13

If I understand correctly, this means you can't back up the private key, correct? It's in the Secure Enclave, so if you lose your laptop, you also lose the key? Since it looks like export only really exports the public key not the private one? Probably not the worst thing, you most likely have another way to get into the remote machine, or an admin who can reset you, but still feels like a hole. Or am I missing somet…

[deleted]

Re: Native Secure Enclave backed SSH keys on macOS

#40

Post by johnisgood »

epistasis wrote: post #30
johnisgood wrote: post #26

Earlier quoted context omitted.

Yeah, that is why you should not [always (depends on your use case)] generate it on a YubiKey. You need to have: - an offline master private key backup (air-gapped) - primary YubiKey (daily use) - backup YubiKey (locked away) - revocation certificate (separate storage) (it is your kill-switch) Having a second YubiKey enrolled is the standard practice. What people do wrong is: - They generate directly on YubiKey - The…

I can understand revocation for GPG, but is revocation ever used for SSH? I could understand it if SSH certificates are used, but honestly I've never encountered an org using SSH's cert system.

Well, OpenSSH has a built-in key revocation mechanism (KRL which is just SSH revocation), and there are SSH certificates (with a CA) and certificate revocation, and there is ad-hoc "revocation" by removing keys from the "authorized_keys" file.

If you use your GPG key for SSH, the servers that have your public key do not automatically know that your GPG key was revoked, and SSH authentication will proceed unless you remove the public key from the server OR the server uses an SSH CA/KRL model.

All in all, SSH supports real revocation, but it must be enforced by the server. It is different from GPG where revocation follows the key, not the server.

I have not used KRL myself, but I sort of know how it works. You can generate a new empty KRL, then add keys to revoke, and then to distribute the KRL to servers by configuring OpenSSH to use the KRL file, by adding "RevokedKeys /etc/ssh/revoked_keys.krl" to "/etc/ssh/sshd_config".

The pros of KRL is that they scale better than manual removal for multiple servers, and you can revoke entire CA ranges instead of individual keys if using SSH certificates which is recommended for large setups.

I hope I could clear some things up. Let me know if you have any questions though!

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