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 something?
ps. It amuses me that my Mac won't let me type Secure Enclave without automatically capitalizing it.
Edit: I understand good security is having multiple keys, I was simply asking if this one can be backed up. OP answered below and is updating their webpage accordingly.
Check out `man sc_auth`. There's also an exportable variant where the private key is encrypted using the secure enclave as opposed to generated on the secure enclave:
% sc_auth create-ctk-identity -l ssh-exportable -k p-256 -t bio
% sc_auth list-ctk-identities
p-256 A581E5404ED157C4C73FFDBDFC1339E0D873FCAE bio ssh-exportable ssh-exportable 23.11.26, 19:50 YES
% sc_auth export-ctk-identity -h A581E5404ED157C4C73FFDBDFC1339E0D873FCAE -f ssh-exportable.pem
Enter a password which will be used to protect the exported items:
Verify password:
You can then re-import it on another device
% sc_auth import-ctk-identities -f ssh-exportable.pem.p12 -t bio
Enter PKCS12 file password:
Is there a way to import an existing (compatible) key and still mark it as non-exportable?
That seems more useful for the SSH key scenario: Generate a key in memory and back it up to offline storage once, and otherwise only use it in a way totally non-exportable by any malware.
This sentence
> The exportable private key is encrypted with Elliptic Curve Encryption Standard Variable IVX963 algorithm which is backed by a Secure Enclave key.
makes it sound like exportable keys might inherently not be Secure Enclave resident in Apple's implementation, which would be unfortunate, as anything else can still be accessed by malware with kernel-level privileges.
(GPG, and I believe also PIV, allow importing externally-generated keys without necessarily marking them exportable; they'll just, correctly, lack any attestation statement about having been generated in secure hardware.)
The key is stored encrypted with a unique symmetric key that only your secure enclave knows until the point that you export it. It then re-encrypts it with the password.
Until you export it it's just as strong as an enclave-generated one.
Obviously don't keep the exported password encrypted key around and don't use a weak password for export.
>The key is stored encrypted with a unique symmetric key that only your secure enclave knows until the point that you export it. It then re-encrypts it with the password.
But what's the security benefit of this compared to having a keyfile? So far as I can tell from the commands you provided, there's no real difference, aside from a hacker having to modify their stealer script slightly.
Why is it more secure: a key file on disk is decrypted into memory every time you enter your passphrase. It means the key is around in plain text in the memory of ssh or ssh-agent. Which means it's extractable by an attacker.
An exportable key does all the signing inside the secure enclave and never exposes the decrypted key to OS memory.
The exported key you can keep in a safe for disaster recovery. You shouldn't keep it on your computer of course.
>It means the key is around in plain text in the memory of ssh or ssh-agent. Which means it's extractable by an attacker. An exportable key does all the signing inside the secure enclave and never exposes the decrypted key to OS memory.
But malware can just tell the secure enclave to export the key? Yes, they'll have to write new code to do that, but it's not particularly hard (it's 1 line code from your example above), and it's security through obscurity.
The export operation is guarded by TouchID. So the malware needs to trick you into performing the TouchID gesture.
But yeh the malware only needs to trick you to hit TouchID once. Instead of on each sign operation. So if that's in your threat model don't make the key exportable.
> That's not meaningfully more difficult than tricking you into revealing your key file password.
No, but that's meaningfully more difficult to do without an intervention from the user. Say your computer is infected, the malware won't silently do it: it will have to interact with you.
And an important part is that you apparently don't have to make the key exportable:
> So if that's in your threat model don't make the key exportable.
Which now makes it meaningfully more difficult to extract.
I would personally not export it, just like I don't export (and can't export) the key from a security key. That's a feature.
> Say your computer is infected, the malware won't silently do it: it will have to interact with you.
MacOS is so needy about all kinds of fingerprint/password-related things (and has no context of secure desktop) that it is trivial for malware to simulate and no way for the user to tell whether it's genuine, so it's not a real barrier at all.
As a user I prefer a single touch to typing a passphrase every time. A passphrase also has other attack vectors like keylogging, etc., which would allow replays.
But even if security was exactly the same, I'd prefer the touch to the typing.
So it just has to wait until you’re about to do a legitimate operation requiring authentication, intercept that to export the key, and cancel the real one with a bogus error (and you’ll just try again without any second thoughts).
MacOS has also no concept of secure desktop/etc where the OS can use some privileged UI to explicitly tell you what you are signing and prompt for PIN/biometrics. It’s in fact a well-known problem where legitimate dialogs for system/Apple ID password have no distinguishing features from fake ones.
Unlike a TPM and like a YubiKey, you can configure the secure enclave to require presence (via Touch ID) so that a stealer script would be stopped with a prompt.
Until the next time you touch your Touch ID for any other operation. It seems realistic for an attacker script to anticipate that and open its own prompt at the right moment (i.e. with your finger already on the way to the button).
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.
Keep the private key you actively use in the secure enclave. The system you actively use is most at risk.
Keep a secondary offline private key as backup. You can generate and store it in a secure location, and never move it around. Airgapped even if you want. You could even use a yubikey or other hardware for the secondary key giving you two hard to export keys.
That can work really well for systems where you don't need to share your key material very often, or where sharing is optimized for n-key scenarios.
SSH isn't always that. For example, ssh-copy-id by default does not copy over multiple identities.
For that reason, I'd personally prefer to import my (otherwise airgapped) key into my secure hardware exactly once and mark it as non-exportable in the SSH scenario.
It’s important to remember that over time systems develop complexities that can be hard to recover from scratch because by definition air gapped data aren’t ones you are regularly exercising. Here’s an example of this in action from Google’s history
Yeah but if you get a new device, you have to go add its pubkey to every server you ever use. I wish there were an easier way, otherwise it's understandable that people copy privkeys.
> if you get a new device, you have to go add its pubkey to every server you ever use
It’s not too bad, if the number of servers is not too high.
I have different client pub keys on my phone, multiple laptops and desktop computers and manage my authorized keys to be able to ssh into my servers from the devices, as well as from one laptop to another or from my phone to one of the laptops, etc.
Because I already have several client devices I don’t really need any backup ssh keys. The fact that each device has a different key means that if one laptop breaks or my phone is stolen, I can still ssh into everything from one of the remaining devices and remove the pub key of the broken or stolen device from authorized keys and generate new keys on new devices and then using one of the existing devices to add the pub key of the new device to the authorized keys of the servers and other devices.
For me it’s manageable to do it manually. But if you have very many servers you’d probably want to use a configuration management tool like Chef, Ansible, Puppet or Saltstack. Presumably if you have a very high number of servers you’d already be using a configuration management tool like one of those for other configs and setup anyways.
If you’re operating at the scale this is too cumbersome to do manually surely you already have a configuration management system in place to automate this no?
I have keys tied to several random things, including home servers, GitHub, and AWS. Wouldn't call this scale exactly, but when I got a new laptop, it was way easier to just copy .ssh onto it rather than hunting everything down.
Today I make a private/public keypair, and the private key is on my laptop in my encrypted home folder. It also gets backed up to my encrypted offsite backup. That way if my laptop breaks or is stolen, I can restore from backup and be up and running as before.
I was simply asking if that is still possible with this method, nothing more.
And not every service that uses ssh auth allows multiple keys.
As others mention, there is no point to using the Secure Enclave if you have your key stored on disk or in your backup. It’s like putting impressive locks on the front door, while leaving the window open.
Beyond that, you can do that just fine right now by making TWO keys. If you lose the laptop, oh well. Recover with your backup key (which is hopefully kept more securely than you describe - it can be inconvenient to access since it is only needed for recovery).
This also lets you go further in loving things down or providing you notifications, as you can distinguish server side between your usual key and the backup key.
The point of the enclave is to be noncloneable and access limited. Extracting the key for the backup would negate the benefits derived from that.
It’s possible but would not bring you any extra security.
The advantage of non-exportable, HSM-backed keys is that you are guaranteed that the only way to use that key is to have online access to the HSM, and you can recover from HSM access compromise without having to replace the keys.
If you make the key exportable it is no better than if it was stored on your disk to begin with.
yes, you can export keys using this method, and they will be simlarly secure as password encrypted keys you generate without the secure enclave with openssh, but with the convenience that you can decrypt the key using TouchID on macOS.
Such a setup is marginally more secure than just typing in the passwords, since it is much harder to intercept the TouchID chain from touch to decrypting the SSH key compared to your keyboard to the terminal.
All that said, here are the priorities of a few security technologies:
TouchID:
#1 environment integrity, that is to say, to protect Apple services monopolies and fees such as eliminating password sharing of services accounts, #2 convenience as an alternative to passwords reducing friction when you buy stuff, #3 security.
1password:
#1 convenience, #2 security
I cannot tell you really what is "#1" in security among packaged ready to buy commercial products, Everyone, practically, makes affordances for convenience ahead of security. I suppose there isn't really a great product for normal people that puts security first. Of course, there are an ad hoc collection of practices that amount to, #1 security. But a product? No. Even Apple Lockdown mode... well, they can still just push an update that makes it pretend it is enabled when it is not, so...
> if you don't balance security theory with operational practice, critical business functions can fail
i.e. people will circumvent the secure-but-onerous path. (I don't think they can be faulted for trying to get their work done either, I'm agreeing with you)
In this case you can maintain an offline SSH CA and trust that on the remote machines, and then sign yourself leaf certificates against a non-exportable HSM-backed key. In case of loss you just make a new key and sign a new certificate.
Of course this just moves the key management problem somewhere else: now you need to protect the CA key, but that might be easier since you would only need access to it in a disaster recovery scenario if you replaced the laptop or otherwise lost access to your HSM-backed key.
Keeping the certificate’s key as non-exportable in the HSM means you do not need to revoke it as it cannot be compromised (not permanently at least), once you’ve regained access to the HSM you can assume the bad guys are out.
Of course the CA key itself is another story, which is why this merely moves the problem elsewhere (however since you only need access to the CA during initial provisioning of a new certificate key, you can better control access to it).
> Keeping the certificate’s key as non-exportable in the HSM means you do not need to revoke it as it cannot be compromised (not permanently at least), once you’ve regained access to the HSM you can assume the bad guys are out.
How so? I can still lose my Yubikey, and even if the attacker can't export the private key corresponding to a CA-signed SSH certificate, they can still use it, no? How would I "regain access" in this scenario?
I was thinking the HSM in this case is your Macbook and its TPM/Secure Enclave, in which case you'd either recover it or assume the attacker is unable to use it due to biometrics/PIN. I guess the Yubikey has a PIN too with a limited number of tries.
Either way, you either recover the HSM and then don't need to rotate the keys, or you don't in which case you either use OpenSSH's key revocation mechanism (which I believe involves distributing some some sort of CRL to every server), use time-limited SSH certificates and wait out the expiry of the compromised key, or scrap the whole CA and start fresh.
Again this depends on your threat model. The somewhat uncommon requirement where you can't manage your own `authorized_keys` on the remote host complicates things a lot; if you could, then you'd use your existing access (sign yourself a new certificate using your SSH CA) to rotate the whole CA... or just keep two keys in there (primary and backup) and skip the whole CA dance, since it's purely a workaround for the hard requirement of only being able to put one key in authorized_keys.
No but that’s the point. If there’s a copy of the private key out there, then it can be copied. The whole point is that the jedberg-laptop-1 key only ever exists as jedberg-laptop-1. When that laptop gets lost/stolen/destroyed/aged out, there's 100% certainty that it can't be recreated. The other side of that equation is that you need a tree of keys and a whole IT department to manage them so you don't get locked out of your servers. This particular bit of software is about ssh keys and exists within a larger conversation about PKI which you know more about than I, but operationally, you have this, and then you have a root login private key file locked with Shamir secret sharing (ssss on debian) that you distribute to a very select few number of key bearers. And then don't all get on the same plane together, ever.
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.
Any malware capable of exfiltrating a file from your home folder is also capable of calling the export command and tricking you into providing biometrics.
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
- They only use one device
- They do not create a revocation certificate
- They have no offline backups
You generate your GPG keys on a secured system, load the subkeys (not the master because it is not used for daily cryptography) into the YubiKeys, and then remove the secret keys from this system where you generated the keys.
Does OpenSSH's `sshd` even support GPG key revocation? (Assuming you're talking about using the GnuPG card application of Yubikeys, since the newer "native" FIDO security key implementation of OpenSSH does not support importing existing keys to my knowledge.)
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!
A lot of absolutes are being thrown around in the comments here, unfortunately. It really depends on your scenario.
Generating keys exclusively in (non-backup-able) secure hardware is great if your scenario readily supports multiple keys per server/domain you're authenticating in.
Creating an airgapped backup and loading that into a "daily driver" Yubikey marked as non-exportable can be perfectly fine if that's not the case and you don't want to notify the world every time you're adding or retiring a new Yubikey (for reasons other than key compromise).
Depends on your use case, and you will still have to generate your master key offline even if you want the subkeys generated directly on each YubiKey, which then you sign with the master key.
It is only slightly less secure if you pre-generate subkeys on an offline machine if you want identical subkeys on multiple devices (and if you want exact backups). Sometimes this is exactly what people want.
Ultimately it really depends on your use case.
BTW, please check the parent comments to which I responded.
PS. I think it would be useful for others if you elaborated on your statements (for educational purposes).
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.
This is true for passkeys/webauthn/u2f, which is why it’s trash and a completely flawed and not fit for purpose standard (of course the primary purpose is vendor lock-in, not reliable and disaster-proof authentication).
But SSH allows you to export the public key and then you can enroll it on as many hosts as you want without needing access to the private key, so the backup key can remain in a safe, ideally forever as you should never need it.
I agree that it's inconvenient in many cases, but what vendor am I being locked into, exactly? My primary hardware key can be from a completely different vendor than the backup one, so I don't quite buy the conspiracy angle.
There's also no technical obstacle preventing anyone from creating "paired" hardware authenticators that share the same internal root derivation key and can as such authenticate to all services (at least if they don't demand resident credentials) that were registered to any of the keys in the set.
The fact that these keys don't exist on the market (I believe Yubikey looked into them a while ago) more is evidence for the lack of demand, and less for the existence of a cabal, in my view.
Being locked into a set of a handful of vendors who offer "secure" sync (of course, this is not a true PKI and actual key material is being synced, meaning it's only as secure as the syncing protocol and your authentication to it).
> My primary hardware key can be from a completely different vendor than the backup one, so I don't quite buy the conspiracy angle.
The fundamental flaw is that enrolling an authenticator requires it to be present, making a backup strategy much less resilient as it means your secondary device needs to be constantly present and thus exposed to the same local/environmental risks the primary one is (theft/fire/faulty USB port that fries everything plugged in and you only realize after nuking both your keys). It makes an offline backup scenario like with SSH (where you copy a public key and otherwise leave the authenticator out of reach in a safe place) impossible.
Making it hard/impractical to maintain a reliable backup yourself sure makes those proprietary sync-based services attractive, which also doubles as reducing security since key material is being synced and can potentially be extracted (impossible with a true HSM + PKI implementation).
> preventing anyone from creating "paired" hardware authenticators
Don't certain types of keys involve writing something to the authenticator, fundamentally preventing this (as the backup authenticator won't get this written value)?
> cabal
It doesn't have to be explicit coordinated action like intentionally wanting to prevent people from self-managing passkeys (in fact any hint of it being intentional would be a liability in a potential anti-trust situation, so that's a big no-no); it can be done by simply omitting this scenario, by accident or for "security" purposes, or deprioritizing it to hell. In fact the Credential Migration spec is still a draft and appears quite recent, despite passkeys being heavily promoted for a while: https://fidoalliance.org/specs/cx/cxp-v1.0-wd-20241003.html - you'd think that such as basic feature would be sorted before the push to switch to passkeys no?
> For the initial delivery of Credential Exchange, we focused on the most wide use case [emphasis mine]
"Initial" delivery focuses on the most widespread use-case (how convenient it also happens to be the most corporation-friendly use-case), with everything else coming "later", meaning never. I'm sure it'll rot in some Jira backlog as a liability shield so they can promise they did plan for it and just never got around to it, but everyone understands it will never actually get implemented.
How can the "cartel" "blacklist" anyone? The only thing the FIDO alliance can do is not include a vendor's attestation key as trusted in their vendor database, and software solutions aren't on that list to begin with.
> The fundamental flaw is that enrolling an authenticator requires it to be present [...]
Yes, but that doesn't mean you can't backup the full authenticator state.
Here's a toy WebAuthN implementation that is backed by a passphrase that you remember or write on a piece of paper which works on many websites supporting passkeys and not enforcing attestation (which is the vast majority, since Apple, Google, 1Password, and Bitwarden all don't support attestation for synchronized credentials a.k.a. passkeys): https://github.com/lxgr/brainchain
> Making it hard/impractical to maintain a reliable backup yourself sure makes those proprietary sync-based services attractive
It's also completely open source and can be backed up :) (But again, it's a toy demo – don't use it for anything sensitive!)
All they have to do is publish a "best practices" statement or some RP certification program mandating attestation to be used (and some PR around how only "certified" RPs are secure) and job done. The only reason they didn't do that yet is that Apple is refusing to play ball and support attestation (but this may change).
The threat was clearly there in the original Github issue, and it's just a temporary inconvenience they can't currently follow through on it.
> Yes, but that doesn't mean you can't backup the full authenticator state.
Having the secondary authenticator present in the same vicinity as the primary one exposes it to risks. Having to dump authenticator state at regular intervals now means your backup authenticator must be reachable for writing online, so it can't be a simple "cold storage" backup like a Yubikey in a safe anymore. This also opens up security concerns since you're now dumping and syncing private keys left and right over a network and you lose the peace of mind of using an HSM-backed non-exportable private key where the HSM being unplugged guarantees nobody is currently using your keys.
Seems like a shit ton of complexity and effort to work around a problem OpenSSH elegantly solved 30 years ago.
> Here's a toy WebAuthN implementation
Thanks, I will check it out and read up on it. I'd be genuinely happy to move to WebAuthn if I could build my own hardware authenticators that allow the backup one to remain fully offline in a safe, and not have private keys flying around (if I'm doing that, it's not much of an improvement over syncing passwords - except those I can at least type or tell over the phone in an emergency when I need someone else to act on my behalf).
Edit: so it seems like I am mostly right? Only discoverable credentials count as "passkeys", and those generate per-site private keys, meaning offline, cold-storage backups are impossible. I guess I'm sticking to my password manager then since passkeys would provide no improvement in this case.
Nonetheless I'm glad to hear about it. I don't yet use YubiKeys for FIDO, because I was concerned a bit about this enrollment process, and hadn't bothered to figure out what others do.
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.
Yes, that's the point, indeed. One key per device, impossible to extract, so you need to break into the device to use the key.
If you want to maintain backup access, you can use an SSH CA to sign your public SSH keys, then keep the private keys on your device. If you keep the CA keys safe (i.e. physically safe on a flash drive), this means you can even add new keys after you lose all your devices.
This way, you only need to trust your one CA on your servers (so you don't need to copy 20 public keys around for every server).
Plus, if you're setting up a (separate) SSH CA, you can also sign servers' host keys, so you don't need to rely on TOFU to prevent MITM attacks, if that's something you care about.
If you're willing to go a bit further you can also do GPG signing with ECDSA, though it requires a patched GPG due to bugs and a patched SSH agent that allows raw signing. We have a packaged version with a macOS UI [0], but the same backend [1] works on Linux using the tpm via PKCS#11.
We have a blog post on this, but I guess it was never made public, but the only difference between GPG and SSH is the way in which keys and signatures are wrapped and listed through the various layers -- it's all just fundamentally ECDSA with a named curve.
I've been using Secretive for years, and prefer it to all the physical key/card based systems I've tried to get going over the years. I know exactly when my SSH key is used for any operation, because I need to hit a button or do a fingerprint scan. I can keep ssh-agent tunnels to remote boxes so that I can sign git commits remotely without having to worry about a rogue system getting complete access to key ops without me knowing what's going on.
However the Tahoe version of secretive is buggy and frequently locks up on initial key op requests. I don't have the bandwidth to debug it and file a bug report, and honesty I'm not sure I want to relearn all that knowledge of SSH to figure it out.
I think the smart card SSH UX is worse than secretive's, IIRC my past pain, but if it is reliable, worth a shot.
> I can keep ssh-agent tunnels to remote boxes so that I can sign git commits remotely without having to worry about a rogue system getting complete access to key ops without me knowing what's going on.
I also really like secretive, but at least this part is not exclusive to it; OpenSSH's `ssh-agent` and `ssh-add` have long supported confirmation of each private key use with `ssh-askpass` (although it unfortunately can't distinguish between remote and local key uses).
It's a golang library that abstracts usage of ssh keys backed by hardware on all sorts of devices - mostly designed for laptops, but supports Linux, Windows and MacOs
How can I get such a key into my iPhone too, so that I can sign emails and file and such with the same private key when I'm on my phone, and my public key is valid for all such operations ? Will iCloud take care of that ? And then I want it all usable from my (multiple) email clients...
What you're thinking of are Passkeys. Which are synced. Somebody would have to write an SecurityKeyProvider that talks to the Passkey API instead.
Actually I don't think it's completely impossible. The only thing is that passkeys are origin-bound. They belong to a specific AppBundle ID or domain name. If say Secretive would add passkey support then that specific public/private keypair can't be used by another app. Though it does sync across instances of the app across devices.
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)
Probably for the same reason that OpenSSH's `sk` implementation also still needs a private key file (even for the "resident key" option): You need to be able to point OpenSSH's various tools to something in an identity context, and that something traditionally is a private key file.
The article even mentions that it doesn't contain any sensitive data:
> Note that the "private" key here is just a reference to the FIDO credential. It does not contain any secret key material.
It's a slightly different story for non-resident `sk`-backed keys; these actually require the private key file since the hardware authenticator itself is (or at least can be) stateless. (It's still not a security risk if it ever leaks, but it's an availability risk if it's ever lost.)
Not sure if macOS's backing implementation is stateful or stateless (or some unfortunate hybrid of both; i.e., it might just store a stateful wrapped key in some system-level keychain in a way that intransparently breaks if the OS is ever reinstalled, but also doesn't allow querying an intact system for any existing credentials).
Oh, this is neat! I wonder if apple just added support for the secure enclave as a provider or if this might help fix the bad experience of yubikeys on the mac. Last time I tried it, the distributed ssh and ssh-agent didn't play well with security keys
I've heard people make the point before that EdDSA is not great for secure enclaves due to being suspictable to Fault Attacks which could lead to (partial) key extraction
I don't trust the NIST curves: they were generated in a dubious way which has been written about extensively elsewhere (the coefficients for P-256 were generated by hashing the unexplained seed c49d360886e704936a6678e1139d26b7819f7e90). I always avoid them unless I have to use them. It makes me sad when hardware forces me to use them.
> I've heard people make the point before that EdDSA is not great for secure enclaves due to being suspictable to Fault Attacks which could lead to (partial) key extraction
Huh, got a link? My understanding is that eddsa is better with respect to side channels in every way, that was part of the intent of it's design. I've worked with crypto hardware which supports it.
Some Fido2 keys like the YubiKey and Nitrokeys support PGP keys as well. Works pretty nice as well and has the added bonus of your key not being tied to a pice of hardware that is as likely to break like a laptop (or be upgraded on a semi-regular basis)
You can (mis)use ssh keys for git signing, but GPG on gpg-card and S/MIME on PIV card are the two standards and their respective hardware implementations (for signing keys in general.)
If the Secure Enclave on your Mac is backdoored, the fact that the key from your Yubikey (or whatever HSM) is un-extractable will be a very cold comfort.
It's a total pain in the ass to try to have password encrypted gpg or ssh keys in mac. Nothing better that another way to make it even more painful and complicated, so that people will just store plain text keys to not be annoyed.
> It's a total pain in the ass to try to have password encrypted gpg or ssh keys in mac.
Who uses password encrypted keys anyway ? No exfiltration protection, and a sitting duck for unlimited automated password guessing attempts.
Pre-Tahoe people used Yubikeys or Secretive. But now this native tool is a better option than Secretive, even if Yubikeys still have their uses for the power-users.
With an ssh agent and time-bounded key expiration one can have very strong password on the key that is convenient to use.
Also password managers like 1password or Bitwarden support ssh-agent protocol so one can have a master password that protects both stored passwords and keys.
Edit: I'm not suggesting an ssh key with a passphrase (or password) is better than what the article suggests; I'm only saying that adding a passphrase (or password) to an ssh key at least buys time to address the situation while the attacker is trying to break the encryption on the stolen key.
I am anti-Mac in every way, but I do use passphrase protected ssh keys so if someone were to get a copy of my ssh key, they would have to be able to break the encryption to use the key. I see a lot of devs using blank passphrases on their ssh keys, smh.
> sitting duck for unlimited automated password guessing attempts.
Using a passphrase on your ssh key has nothing to do with whether the ssh service is configured to allow or deny passwords.
> whether the ssh service is configured to allow or deny passwords.
Given the consistent use of "password" instead of "passphrase", I think they meant an exfil'ed encrypted key is vulnerable to no-rate-limit bruteforcing, in contrast with hardware-backed keys.
Right, but my context is that devs often use no passsphrase at all. If someone can get a copy, they have instant access to whatever it has access to. They don't need to even break encryption since the key has none if none has been applied. My stance is simply, at least add a passphrase to the key (though some call it a password).
The parent means that an attacker has unlimited attempts at breaking the passphrase on an exfiltrated key. Once the key passphrase is broken, they can log in using the key.
I've used password-encrypted keys on a Mac plenty of times. It was easy to add them to the SSH agent to not require a password after initial authorization, if that's what I wanted. What is the issue I'm not seeing?
> It's a total pain in the ass to try to have password encrypted gpg or ssh keys in mac
I'm anti-Mac but for the year recently that I had to use one at work, no choice...I had no issues, none, using gpg or using a passphrase on my ssh keys.
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 something?
ps. It amuses me that my Mac won't let me type Secure Enclave without automatically capitalizing it.
Edit: I understand good security is having multiple keys, I was simply asking if this one can be backed up. OP answered below and is updating their webpage accordingly.
Check out `man sc_auth`. There's also an exportable variant where the private key is encrypted using the secure enclave as opposed to generated on the secure enclave:
You can then re-import it on another device I'll add this to the guideIs there a way to import an existing (compatible) key and still mark it as non-exportable?
That seems more useful for the SSH key scenario: Generate a key in memory and back it up to offline storage once, and otherwise only use it in a way totally non-exportable by any malware.
This sentence
> The exportable private key is encrypted with Elliptic Curve Encryption Standard Variable IVX963 algorithm which is backed by a Secure Enclave key.
makes it sound like exportable keys might inherently not be Secure Enclave resident in Apple's implementation, which would be unfortunate, as anything else can still be accessed by malware with kernel-level privileges.
(GPG, and I believe also PIV, allow importing externally-generated keys without necessarily marking them exportable; they'll just, correctly, lack any attestation statement about having been generated in secure hardware.)
How is this method any different from encrypting the private key without any secure enclave?
Isn't it just using a password derived key?
The key is stored encrypted with a unique symmetric key that only your secure enclave knows until the point that you export it. It then re-encrypts it with the password.
Until you export it it's just as strong as an enclave-generated one.
Obviously don't keep the exported password encrypted key around and don't use a weak password for export.
>The key is stored encrypted with a unique symmetric key that only your secure enclave knows until the point that you export it. It then re-encrypts it with the password.
But what's the security benefit of this compared to having a keyfile? So far as I can tell from the commands you provided, there's no real difference, aside from a hacker having to modify their stealer script slightly.
Why is it more secure: a key file on disk is decrypted into memory every time you enter your passphrase. It means the key is around in plain text in the memory of ssh or ssh-agent. Which means it's extractable by an attacker. An exportable key does all the signing inside the secure enclave and never exposes the decrypted key to OS memory.
The exported key you can keep in a safe for disaster recovery. You shouldn't keep it on your computer of course.
>It means the key is around in plain text in the memory of ssh or ssh-agent. Which means it's extractable by an attacker. An exportable key does all the signing inside the secure enclave and never exposes the decrypted key to OS memory.
But malware can just tell the secure enclave to export the key? Yes, they'll have to write new code to do that, but it's not particularly hard (it's 1 line code from your example above), and it's security through obscurity.
The export operation is guarded by TouchID. So the malware needs to trick you into performing the TouchID gesture.
But yeh the malware only needs to trick you to hit TouchID once. Instead of on each sign operation. So if that's in your threat model don't make the key exportable.
> So the malware needs to trick you into performing the TouchID gesture.
That's not meaningfully more difficult than tricking you into revealing your key file password.
>Instead of on each sign operation.
But from your video each sign operation also requires a touchid prompt?
> That's not meaningfully more difficult than tricking you into revealing your key file password.
No, but that's meaningfully more difficult to do without an intervention from the user. Say your computer is infected, the malware won't silently do it: it will have to interact with you.
And an important part is that you apparently don't have to make the key exportable:
> So if that's in your threat model don't make the key exportable.
Which now makes it meaningfully more difficult to extract.
I would personally not export it, just like I don't export (and can't export) the key from a security key. That's a feature.
> Say your computer is infected, the malware won't silently do it: it will have to interact with you.
MacOS is so needy about all kinds of fingerprint/password-related things (and has no context of secure desktop) that it is trivial for malware to simulate and no way for the user to tell whether it's genuine, so it's not a real barrier at all.
As a user I prefer a single touch to typing a passphrase every time. A passphrase also has other attack vectors like keylogging, etc., which would allow replays.
But even if security was exactly the same, I'd prefer the touch to the typing.
The malware would have to prompt for biometric authentication before exporting.
So it just has to wait until you’re about to do a legitimate operation requiring authentication, intercept that to export the key, and cancel the real one with a bogus error (and you’ll just try again without any second thoughts).
MacOS has also no concept of secure desktop/etc where the OS can use some privileged UI to explicitly tell you what you are signing and prompt for PIN/biometrics. It’s in fact a well-known problem where legitimate dialogs for system/Apple ID password have no distinguishing features from fake ones.
> The exported key you can keep in a safe for disaster recovery.
No. Your "disaster recovery" should be either a second device with a Secure Enclave, or a Yubikey.
Making it exportable from the Secure Enclave defeats the whole purpose.
Unlike a TPM and like a YubiKey, you can configure the secure enclave to require presence (via Touch ID) so that a stealer script would be stopped with a prompt.
Until the next time you touch your Touch ID for any other operation. It seems realistic for an attacker script to anticipate that and open its own prompt at the right moment (i.e. with your finger already on the way to the button).
“ This is might be considered secure but is convenient for key backup.”
Might want to clean up that sentence.
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.
You can use more than one key you know.
Keep the private key you actively use in the secure enclave. The system you actively use is most at risk.
Keep a secondary offline private key as backup. You can generate and store it in a secure location, and never move it around. Airgapped even if you want. You could even use a yubikey or other hardware for the secondary key giving you two hard to export keys.
Distribute pub keys for both of them.
Best of both worlds?
That can work really well for systems where you don't need to share your key material very often, or where sharing is optimized for n-key scenarios.
SSH isn't always that. For example, ssh-copy-id by default does not copy over multiple identities.
For that reason, I'd personally prefer to import my (otherwise airgapped) key into my secure hardware exactly once and mark it as non-exportable in the SSH scenario.
It’s important to remember that over time systems develop complexities that can be hard to recover from scratch because by definition air gapped data aren’t ones you are regularly exercising. Here’s an example of this in action from Google’s history
https://google.github.io/building-secure-and-reliable-system...
Yeah but if you get a new device, you have to go add its pubkey to every server you ever use. I wish there were an easier way, otherwise it's understandable that people copy privkeys.
> if you get a new device, you have to go add its pubkey to every server you ever use
It’s not too bad, if the number of servers is not too high.
I have different client pub keys on my phone, multiple laptops and desktop computers and manage my authorized keys to be able to ssh into my servers from the devices, as well as from one laptop to another or from my phone to one of the laptops, etc.
Because I already have several client devices I don’t really need any backup ssh keys. The fact that each device has a different key means that if one laptop breaks or my phone is stolen, I can still ssh into everything from one of the remaining devices and remove the pub key of the broken or stolen device from authorized keys and generate new keys on new devices and then using one of the existing devices to add the pub key of the new device to the authorized keys of the servers and other devices.
For me it’s manageable to do it manually. But if you have very many servers you’d probably want to use a configuration management tool like Chef, Ansible, Puppet or Saltstack. Presumably if you have a very high number of servers you’d already be using a configuration management tool like one of those for other configs and setup anyways.
There is an easier way: Create a SSH CA, add that to your authorized_keys everywhere, use it to sign the individual public keys.
Yep that's what I do! I have two ssh-ca's stored on two Yubikeys. And both are trusted by my servers.
If I lose one I can still sign new certs with the other.
https://github.com/arianvp/nixos-stuff/blob/master/modules/s...
But now you need to worry about revocation or at least key lifetimes.
If you’re operating at the scale this is too cumbersome to do manually surely you already have a configuration management system in place to automate this no?
I have keys tied to several random things, including home servers, GitHub, and AWS. Wouldn't call this scale exactly, but when I got a new laptop, it was way easier to just copy .ssh onto it rather than hunting everything down.
I think you are mixing up concerns. You need a backup key. That doesn't mean you need to backup your key.
Anything (everything?) using SSH authentication supports multiple authentication keys. Have a yubikey in a locked deposit box or something.
Today I make a private/public keypair, and the private key is on my laptop in my encrypted home folder. It also gets backed up to my encrypted offsite backup. That way if my laptop breaks or is stolen, I can restore from backup and be up and running as before.
I was simply asking if that is still possible with this method, nothing more.
And not every service that uses ssh auth allows multiple keys.
As others mention, there is no point to using the Secure Enclave if you have your key stored on disk or in your backup. It’s like putting impressive locks on the front door, while leaving the window open.
Beyond that, you can do that just fine right now by making TWO keys. If you lose the laptop, oh well. Recover with your backup key (which is hopefully kept more securely than you describe - it can be inconvenient to access since it is only needed for recovery).
This also lets you go further in loving things down or providing you notifications, as you can distinguish server side between your usual key and the backup key.
The point of the enclave is to be noncloneable and access limited. Extracting the key for the backup would negate the benefits derived from that.
If you are keeping it on disk (encrypted or not), you don’t really gain anything from using the Secure Enclave.
It’s possible but would not bring you any extra security.
The advantage of non-exportable, HSM-backed keys is that you are guaranteed that the only way to use that key is to have online access to the HSM, and you can recover from HSM access compromise without having to replace the keys.
If you make the key exportable it is no better than if it was stored on your disk to begin with.
yes, you can export keys using this method, and they will be simlarly secure as password encrypted keys you generate without the secure enclave with openssh, but with the convenience that you can decrypt the key using TouchID on macOS.
Such a setup is marginally more secure than just typing in the passwords, since it is much harder to intercept the TouchID chain from touch to decrypting the SSH key compared to your keyboard to the terminal.
All that said, here are the priorities of a few security technologies:
TouchID:
1password: I cannot tell you really what is "#1" in security among packaged ready to buy commercial products, Everyone, practically, makes affordances for convenience ahead of security. I suppose there isn't really a great product for normal people that puts security first. Of course, there are an ad hoc collection of practices that amount to, #1 security. But a product? No. Even Apple Lockdown mode... well, they can still just push an update that makes it pretend it is enabled when it is not, so...> if you don't balance security theory with operational practice, critical business functions can fail
i.e. people will circumvent the secure-but-onerous path. (I don't think they can be faulted for trying to get their work done either, I'm agreeing with you)
In what scenario would you prefer to backup an SSH key in favor of generating new SSH keys?
When I have my pub key in the authorized_keys files of many machines, especially machines where I don't control the authorized_keys file.
In this case you can maintain an offline SSH CA and trust that on the remote machines, and then sign yourself leaf certificates against a non-exportable HSM-backed key. In case of loss you just make a new key and sign a new certificate.
Of course this just moves the key management problem somewhere else: now you need to protect the CA key, but that might be easier since you would only need access to it in a disaster recovery scenario if you replaced the laptop or otherwise lost access to your HSM-backed key.
As usual, it all depends on your threat model.
But how do you revoke any compromised certificate if you don't control the remote machines?
Keeping the certificate’s key as non-exportable in the HSM means you do not need to revoke it as it cannot be compromised (not permanently at least), once you’ve regained access to the HSM you can assume the bad guys are out.
Of course the CA key itself is another story, which is why this merely moves the problem elsewhere (however since you only need access to the CA during initial provisioning of a new certificate key, you can better control access to it).
> Keeping the certificate’s key as non-exportable in the HSM means you do not need to revoke it as it cannot be compromised (not permanently at least), once you’ve regained access to the HSM you can assume the bad guys are out.
How so? I can still lose my Yubikey, and even if the attacker can't export the private key corresponding to a CA-signed SSH certificate, they can still use it, no? How would I "regain access" in this scenario?
I was thinking the HSM in this case is your Macbook and its TPM/Secure Enclave, in which case you'd either recover it or assume the attacker is unable to use it due to biometrics/PIN. I guess the Yubikey has a PIN too with a limited number of tries.
Either way, you either recover the HSM and then don't need to rotate the keys, or you don't in which case you either use OpenSSH's key revocation mechanism (which I believe involves distributing some some sort of CRL to every server), use time-limited SSH certificates and wait out the expiry of the compromised key, or scrap the whole CA and start fresh.
Again this depends on your threat model. The somewhat uncommon requirement where you can't manage your own `authorized_keys` on the remote host complicates things a lot; if you could, then you'd use your existing access (sign yourself a new certificate using your SSH CA) to rotate the whole CA... or just keep two keys in there (primary and backup) and skip the whole CA dance, since it's purely a workaround for the hard requirement of only being able to put one key in authorized_keys.
No but that’s the point. If there’s a copy of the private key out there, then it can be copied. The whole point is that the jedberg-laptop-1 key only ever exists as jedberg-laptop-1. When that laptop gets lost/stolen/destroyed/aged out, there's 100% certainty that it can't be recreated. The other side of that equation is that you need a tree of keys and a whole IT department to manage them so you don't get locked out of your servers. This particular bit of software is about ssh keys and exists within a larger conversation about PKI which you know more about than I, but operationally, you have this, and then you have a root login private key file locked with Shamir secret sharing (ssss on debian) that you distribute to a very select few number of key bearers. And then don't all get on the same plane together, ever.
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.
Any malware capable of exfiltrating a file from your home folder is also capable of calling the export command and tricking you into providing biometrics.
Correct. Set up multiple keys as backups. Thats also a positive, as nothing can leak the key.
Inability to export the private key is no different from using an YubiKey? You can't "backup" the private key they generate either.
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
- They only use one device
- They do not create a revocation certificate
- They have no offline backups
You generate your GPG keys on a secured system, load the subkeys (not the master because it is not used for daily cryptography) into the YubiKeys, and then remove the secret keys from this system where you generated the keys.
Does OpenSSH's `sshd` even support GPG key revocation? (Assuming you're talking about using the GnuPG card application of Yubikeys, since the newer "native" FIDO security key implementation of OpenSSH does not support importing existing keys to my knowledge.)
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!
You are talking about GPG keys. The featured article only refers to SSH keys. Know the difference.
I know the difference, thank you for your concern.
Do you have a good guide/video/write up on this?
I’ve been putting off remaking my GPG and SSH keys using a Yubikey.
> Yeah, that is why you should not generate it on a YubiKey
No. You should ALWAYS generate on the Yubikey. That's the whole point.
Your backup is one (or more) other keys.
A lot of absolutes are being thrown around in the comments here, unfortunately. It really depends on your scenario.
Generating keys exclusively in (non-backup-able) secure hardware is great if your scenario readily supports multiple keys per server/domain you're authenticating in.
Creating an airgapped backup and loading that into a "daily driver" Yubikey marked as non-exportable can be perfectly fine if that's not the case and you don't want to notify the world every time you're adding or retiring a new Yubikey (for reasons other than key compromise).
Depends on your use case, and you will still have to generate your master key offline even if you want the subkeys generated directly on each YubiKey, which then you sign with the master key.
It is only slightly less secure if you pre-generate subkeys on an offline machine if you want identical subkeys on multiple devices (and if you want exact backups). Sometimes this is exactly what people want.
Ultimately it really depends on your use case.
BTW, please check the parent comments to which I responded.
PS. I think it would be useful for others if you elaborated on your statements (for educational purposes).
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.
This is true for passkeys/webauthn/u2f, which is why it’s trash and a completely flawed and not fit for purpose standard (of course the primary purpose is vendor lock-in, not reliable and disaster-proof authentication).
But SSH allows you to export the public key and then you can enroll it on as many hosts as you want without needing access to the private key, so the backup key can remain in a safe, ideally forever as you should never need it.
I agree that it's inconvenient in many cases, but what vendor am I being locked into, exactly? My primary hardware key can be from a completely different vendor than the backup one, so I don't quite buy the conspiracy angle.
There's also no technical obstacle preventing anyone from creating "paired" hardware authenticators that share the same internal root derivation key and can as such authenticate to all services (at least if they don't demand resident credentials) that were registered to any of the keys in the set.
The fact that these keys don't exist on the market (I believe Yubikey looked into them a while ago) more is evidence for the lack of demand, and less for the existence of a cabal, in my view.
Being locked into a set of a handful of vendors who offer "secure" sync (of course, this is not a true PKI and actual key material is being synced, meaning it's only as secure as the syncing protocol and your authentication to it).
Authenticator implementations who allow exports outside of the vendor cartel are threatened to be blacklisted: https://github.com/keepassxreboot/keepassxc/issues/10407
> My primary hardware key can be from a completely different vendor than the backup one, so I don't quite buy the conspiracy angle.
The fundamental flaw is that enrolling an authenticator requires it to be present, making a backup strategy much less resilient as it means your secondary device needs to be constantly present and thus exposed to the same local/environmental risks the primary one is (theft/fire/faulty USB port that fries everything plugged in and you only realize after nuking both your keys). It makes an offline backup scenario like with SSH (where you copy a public key and otherwise leave the authenticator out of reach in a safe place) impossible.
Making it hard/impractical to maintain a reliable backup yourself sure makes those proprietary sync-based services attractive, which also doubles as reducing security since key material is being synced and can potentially be extracted (impossible with a true HSM + PKI implementation).
> preventing anyone from creating "paired" hardware authenticators
Don't certain types of keys involve writing something to the authenticator, fundamentally preventing this (as the backup authenticator won't get this written value)?
> cabal
It doesn't have to be explicit coordinated action like intentionally wanting to prevent people from self-managing passkeys (in fact any hint of it being intentional would be a liability in a potential anti-trust situation, so that's a big no-no); it can be done by simply omitting this scenario, by accident or for "security" purposes, or deprioritizing it to hell. In fact the Credential Migration spec is still a draft and appears quite recent, despite passkeys being heavily promoted for a while: https://fidoalliance.org/specs/cx/cxp-v1.0-wd-20241003.html - you'd think that such as basic feature would be sorted before the push to switch to passkeys no?
In fact you see this exact strategy playing out: https://github.com/keepassxreboot/keepassxc/issues/11363#iss...
> For the initial delivery of Credential Exchange, we focused on the most wide use case [emphasis mine]
"Initial" delivery focuses on the most widespread use-case (how convenient it also happens to be the most corporation-friendly use-case), with everything else coming "later", meaning never. I'm sure it'll rot in some Jira backlog as a liability shield so they can promise they did plan for it and just never got around to it, but everyone understands it will never actually get implemented.
How can the "cartel" "blacklist" anyone? The only thing the FIDO alliance can do is not include a vendor's attestation key as trusted in their vendor database, and software solutions aren't on that list to begin with.
> The fundamental flaw is that enrolling an authenticator requires it to be present [...]
Yes, but that doesn't mean you can't backup the full authenticator state.
Here's a toy WebAuthN implementation that is backed by a passphrase that you remember or write on a piece of paper which works on many websites supporting passkeys and not enforcing attestation (which is the vast majority, since Apple, Google, 1Password, and Bitwarden all don't support attestation for synchronized credentials a.k.a. passkeys): https://github.com/lxgr/brainchain
> Making it hard/impractical to maintain a reliable backup yourself sure makes those proprietary sync-based services attractive
It's also completely open source and can be backed up :) (But again, it's a toy demo – don't use it for anything sensitive!)
> How can the "cartel" "blacklist" anyone?
All they have to do is publish a "best practices" statement or some RP certification program mandating attestation to be used (and some PR around how only "certified" RPs are secure) and job done. The only reason they didn't do that yet is that Apple is refusing to play ball and support attestation (but this may change).
The threat was clearly there in the original Github issue, and it's just a temporary inconvenience they can't currently follow through on it.
> Yes, but that doesn't mean you can't backup the full authenticator state.
Having the secondary authenticator present in the same vicinity as the primary one exposes it to risks. Having to dump authenticator state at regular intervals now means your backup authenticator must be reachable for writing online, so it can't be a simple "cold storage" backup like a Yubikey in a safe anymore. This also opens up security concerns since you're now dumping and syncing private keys left and right over a network and you lose the peace of mind of using an HSM-backed non-exportable private key where the HSM being unplugged guarantees nobody is currently using your keys.
Seems like a shit ton of complexity and effort to work around a problem OpenSSH elegantly solved 30 years ago.
> Here's a toy WebAuthN implementation
Thanks, I will check it out and read up on it. I'd be genuinely happy to move to WebAuthn if I could build my own hardware authenticators that allow the backup one to remain fully offline in a safe, and not have private keys flying around (if I'm doing that, it's not much of an improvement over syncing passwords - except those I can at least type or tell over the phone in an emergency when I need someone else to act on my behalf).
Edit: so it seems like I am mostly right? Only discoverable credentials count as "passkeys", and those generate per-site private keys, meaning offline, cold-storage backups are impossible. I guess I'm sticking to my password manager then since passkeys would provide no improvement in this case.
> You need the backup available at all times for when you want to register with any new service.
Not for SSH (at least using the OpenSSH sk implementation).
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.
No I got distracted by the word yubikey. Arguably not the same subject. :)
Nonetheless I'm glad to hear about it. I don't yet use YubiKeys for FIDO, because I was concerned a bit about this enrollment process, and hadn't bothered to figure out what others do.
> Which makes yubikey impossible to use with geographically distributed backups.
Huh ?
You do know you can wrap a symmetric key with multiple asymmetric keys, right ?
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.
Yes, that's the point, indeed. One key per device, impossible to extract, so you need to break into the device to use the key.
If you want to maintain backup access, you can use an SSH CA to sign your public SSH keys, then keep the private keys on your device. If you keep the CA keys safe (i.e. physically safe on a flash drive), this means you can even add new keys after you lose all your devices.
This way, you only need to trust your one CA on your servers (so you don't need to copy 20 public keys around for every server).
Plus, if you're setting up a (separate) SSH CA, you can also sign servers' host keys, so you don't need to rely on TOFU to prevent MITM attacks, if that's something you care about.
You use multiple keys, if you need a key usable across different systems then buy a yubikey.
You shouldn’t be backing these keys up anyway imo
If you're willing to go a bit further you can also do GPG signing with ECDSA, though it requires a patched GPG due to bugs and a patched SSH agent that allows raw signing. We have a packaged version with a macOS UI [0], but the same backend [1] works on Linux using the tpm via PKCS#11.
We have a blog post on this, but I guess it was never made public, but the only difference between GPG and SSH is the way in which keys and signatures are wrapped and listed through the various layers -- it's all just fundamentally ECDSA with a named curve.
[0] https://github.com/KeetaNetwork/agent
[1] https://github.com/KeetaNetwork/agent/tree/main/Agent/gnupg/...
Secretive is a bit friendlier to set up but I'll probably switch to this anyway so I have one less app on my computer.
Plugging my blog post for how to achieve this on Windows 11:
https://cedwards.xyz/tpm-backed-ssh-keys-on-windows-11/
Is storing ssh-key in tpm possible on Linux?
https://github.com/Foxboron/ssh-tpm-agent works well for me
Whoa, that is pretty cool.
I've been using Secretive for years, and prefer it to all the physical key/card based systems I've tried to get going over the years. I know exactly when my SSH key is used for any operation, because I need to hit a button or do a fingerprint scan. I can keep ssh-agent tunnels to remote boxes so that I can sign git commits remotely without having to worry about a rogue system getting complete access to key ops without me knowing what's going on.
However the Tahoe version of secretive is buggy and frequently locks up on initial key op requests. I don't have the bandwidth to debug it and file a bug report, and honesty I'm not sure I want to relearn all that knowledge of SSH to figure it out.
I think the smart card SSH UX is worse than secretive's, IIRC my past pain, but if it is reliable, worth a shot.
> I can keep ssh-agent tunnels to remote boxes so that I can sign git commits remotely without having to worry about a rogue system getting complete access to key ops without me knowing what's going on.
I also really like secretive, but at least this part is not exclusive to it; OpenSSH's `ssh-agent` and `ssh-add` have long supported confirmation of each private key use with `ssh-askpass` (although it unfortunately can't distinguish between remote and local key uses).
This exists: https://github.com/facebookincubator/sks.
It's a golang library that abstracts usage of ssh keys backed by hardware on all sorts of devices - mostly designed for laptops, but supports Linux, Windows and MacOs
A golang library is cool, but it doesn't give you a working ssh-agent.
I started working on one few years ago: https://github.com/Foxboron/ssh-tpm-agent
I've been using this for a ~year now and it works very well. Thanks!
How can I get such a key into my iPhone too, so that I can sign emails and file and such with the same private key when I'm on my phone, and my public key is valid for all such operations ? Will iCloud take care of that ? And then I want it all usable from my (multiple) email clients...
These aren't synced over iCloud
What you're thinking of are Passkeys. Which are synced. Somebody would have to write an SecurityKeyProvider that talks to the Passkey API instead.
Actually I don't think it's completely impossible. The only thing is that passkeys are origin-bound. They belong to a specific AppBundle ID or domain name. If say Secretive would add passkey support then that specific public/private keypair can't be used by another app. Though it does sync across instances of the app across devices.
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)
Why would you want the private key file if you store it within the secure enclave?
Probably for the same reason that OpenSSH's `sk` implementation also still needs a private key file (even for the "resident key" option): You need to be able to point OpenSSH's various tools to something in an identity context, and that something traditionally is a private key file.
The article even mentions that it doesn't contain any sensitive data:
> Note that the "private" key here is just a reference to the FIDO credential. It does not contain any secret key material.
It's a slightly different story for non-resident `sk`-backed keys; these actually require the private key file since the hardware authenticator itself is (or at least can be) stateless. (It's still not a security risk if it ever leaks, but it's an availability risk if it's ever lost.)
Not sure if macOS's backing implementation is stateful or stateless (or some unfortunate hybrid of both; i.e., it might just store a stateful wrapped key in some system-level keychain in a way that intransparently breaks if the OS is ever reinstalled, but also doesn't allow querying an intact system for any existing credentials).
Is there a way to make the lifetime of the key last more than a year?
Does anybody know why 'p-384-ne' (instead of 'p-256-ne') cannot be used?
Key can be generated, but 'ssh-keygen -w /usr/lib/ssh-keychain.dylib -K -N ""' cannot find the key to export.
I think this is an openssh limitation.
openssh only supports sk-ecdsa-sha2-nistp256 and sk-ed25519 security keys iirc
Oh, this is neat! I wonder if apple just added support for the secure enclave as a provider or if this might help fix the bad experience of yubikeys on the mac. Last time I tried it, the distributed ssh and ssh-agent didn't play well with security keys
Its worth noting that this is the likely NSA backdoored curve under the hood and probably should not be used.
Does the hardware only support the NIST curves? Or is that just the example that happens to be given?
Only supports NIST curves and ECDSA yes.
I've heard people make the point before that EdDSA is not great for secure enclaves due to being suspictable to Fault Attacks which could lead to (partial) key extraction
I don't trust the NIST curves: they were generated in a dubious way which has been written about extensively elsewhere (the coefficients for P-256 were generated by hashing the unexplained seed c49d360886e704936a6678e1139d26b7819f7e90). I always avoid them unless I have to use them. It makes me sad when hardware forces me to use them.
> I've heard people make the point before that EdDSA is not great for secure enclaves due to being suspictable to Fault Attacks which could lead to (partial) key extraction
Huh, got a link? My understanding is that eddsa is better with respect to side channels in every way, that was part of the intent of it's design. I've worked with crypto hardware which supports it.
https://romailler.ch/project/eddsa-fault/
I think this can be solved by using hedged eddsa (Signal does this)
Does anybody know if there is something similar for gpg keys? E.g. for commit signing?
That is, natively with the Secure Enclave, not exportable.
See my comment above regarding Keeta Agent, which supports GPG and SSH with the same key.
Git commits can be signed with ssh keys.
Some Fido2 keys like the YubiKey and Nitrokeys support PGP keys as well. Works pretty nice as well and has the added bonus of your key not being tied to a pice of hardware that is as likely to break like a laptop (or be upgraded on a semi-regular basis)
You can (mis)use ssh keys for git signing, but GPG on gpg-card and S/MIME on PIV card are the two standards and their respective hardware implementations (for signing keys in general.)
This is just so perfect. No longer a 3rd party glue and separate ssh agent is needed.
Awesome.
Won't be ditching Yubikeys just yet but I can see a number of use-cases for this already.
I’m a bit confused as to why you can export the keys. Can someone explain this?
TFA:
> Note that the "private" key here is just a reference to the FIDO credential. It does not contain any secret key material.
Ah, ok, I missed that bit. Thank you!
I would not trust it personally, specially since the Chip Security Act is looming
https://www.centerforcybersecuritypolicy.org/insights-and-re...
If the Secure Enclave on your Mac is backdoored, the fact that the key from your Yubikey (or whatever HSM) is un-extractable will be a very cold comfort.
nvm
This Gist is about not needing to use Secretive any more.
> Secretive has been around for a while, I don't see why it's coming up now through this gist.
Because this is different !
Secretive required installation, which is both friction and security-sensitive tool written by a third party.
This is native, written by Apple, available out-of-the-box in Tahoe.
It's a total pain in the ass to try to have password encrypted gpg or ssh keys in mac. Nothing better that another way to make it even more painful and complicated, so that people will just store plain text keys to not be annoyed.
> It's a total pain in the ass to try to have password encrypted gpg or ssh keys in mac.
Who uses password encrypted keys anyway ? No exfiltration protection, and a sitting duck for unlimited automated password guessing attempts.
Pre-Tahoe people used Yubikeys or Secretive. But now this native tool is a better option than Secretive, even if Yubikeys still have their uses for the power-users.
With an ssh agent and time-bounded key expiration one can have very strong password on the key that is convenient to use.
Also password managers like 1password or Bitwarden support ssh-agent protocol so one can have a master password that protects both stored passwords and keys.
How short of a time-bound do you use on your SSH keys?
> Who uses password encrypted keys anyway ?
Edit: I'm not suggesting an ssh key with a passphrase (or password) is better than what the article suggests; I'm only saying that adding a passphrase (or password) to an ssh key at least buys time to address the situation while the attacker is trying to break the encryption on the stolen key.
I am anti-Mac in every way, but I do use passphrase protected ssh keys so if someone were to get a copy of my ssh key, they would have to be able to break the encryption to use the key. I see a lot of devs using blank passphrases on their ssh keys, smh.
> sitting duck for unlimited automated password guessing attempts.
Using a passphrase on your ssh key has nothing to do with whether the ssh service is configured to allow or deny passwords.
> whether the ssh service is configured to allow or deny passwords.
Given the consistent use of "password" instead of "passphrase", I think they meant an exfil'ed encrypted key is vulnerable to no-rate-limit bruteforcing, in contrast with hardware-backed keys.
Right, but my context is that devs often use no passsphrase at all. If someone can get a copy, they have instant access to whatever it has access to. They don't need to even break encryption since the key has none if none has been applied. My stance is simply, at least add a passphrase to the key (though some call it a password).
gotcha, thanks for clarifying!
The parent means that an attacker has unlimited attempts at breaking the passphrase on an exfiltrated key. Once the key passphrase is broken, they can log in using the key.
Right, but my context is that devs often use no passsphrase at all. If someone can get a copy, they have instant access to whatever it has access to.
This looks like the complete opposite, though? It’s easy and provides a convenient way to integrate SSH and TouchID.
I've used password-encrypted keys on a Mac plenty of times. It was easy to add them to the SSH agent to not require a password after initial authorization, if that's what I wanted. What is the issue I'm not seeing?
> It's a total pain in the ass to try to have password encrypted gpg or ssh keys in mac
I'm anti-Mac but for the year recently that I had to use one at work, no choice...I had no issues, none, using gpg or using a passphrase on my ssh keys.