Public key identity credentials are credentials built on a pair of cryptographic keys, one kept private and one shared, that let a person or device prove who it is without revealing a reusable secret. Passkeys, smart cards, SSH keys and document signing keys all work on this principle.
This article explains how key pairs function as credentials, how a public key becomes linked to a specific identity, and how to store, back up, rotate and retire keys safely. It is aimed at everyday users adopting passkeys and at developers or administrators managing keys for teams and systems.
A Credential You Never Have to Share
Traditional passwords work like a spoken code word: to prove you know it, you must tell it to the service, which then has to store something derived from it. Every service that holds that information becomes a place where it can leak, and every login is a chance for someone to intercept it.
A public key credential reverses this arrangement. The service stores only a public key, which is safe to publish. To log in, your device uses the matching private key to sign a fresh challenge, and the service checks the signature. The private key itself never travels anywhere.
The practical result is that a breach of the service’s database reveals nothing an attacker can use to sign in as you. Phishing also becomes much harder, since there is no secret for a fake page to collect. These properties explain the steady shift toward key-based credentials for both consumers and organizations.
How Key Pairs Work as Credentials
Public key cryptography, also called asymmetric cryptography, uses two mathematically related keys. Data signed with the private key can be verified with the public key, but knowing the public key does not let anyone calculate the private key with practical computing resources.
A digital signature is the output of applying the private key to a piece of data, such as a login challenge or a document. Anyone with the public key can confirm that the signature was produced by the matching private key and that the data has not changed since it was signed.
For identity purposes, the private key acts as the credential and the public key acts as its fingerprint on record. Proving control of the private key is equivalent to proving you are the registered holder. That is why protecting the private key, rather than hiding the public key, is the central security task.
Binding a Public Key to an Identity
A key pair on its own says nothing about who owns it. Something must link the public key to a person, device or account, and the method chosen determines how much a verifier can trust that link.
Certificates From an Authority
A certificate authority can sign an X.509 certificate stating that a public key belongs to a named person or device. Verifiers who trust that authority can then trust the binding. This model suits organizations and government programs that need strong, centrally managed assurance about who holds each key.
The strength of this binding depends on how carefully the authority checked identity before issuing the certificate.
Registration With a Service
Passkeys and SSH keys usually skip the authority. The public key is registered directly with one service while the user is already signed in or during account creation. The service trusts the key because it saw it enrolled, so the binding is only as strong as that enrollment moment and the account behind it.
This is why services should only accept new keys after a fresh, strong sign-in.
Decentralized and Peer-Based Binding
Some systems publish public keys through decentralized identifiers, known as DIDs, or rely on people vouching for each other’s keys, as in some email encryption communities. These approaches reduce dependence on a single authority but require verifiers to understand and accept a different trust model, which can be harder for everyday users.
Verifiers must also decide how to check that a published key is still current and has not been replaced.
Common Forms of Public Key Credentials
Public key credentials appear under many names, and people often use several without realizing they share the same foundation. Recognizing them helps you apply consistent protection across all of them.
- Passkeys: website and app logins based on the FIDO2 and WebAuthn standards, stored on phones, computers or security keys.
- Smart card keys: private keys on a chip, typically paired with an X.509 certificate for workplace or government login.
- SSH keys: key pairs that administrators and developers use to sign in to servers and code repositories.
- Signing keys: keys used to sign email, documents or software releases so recipients can confirm the author.
- Device keys: keys created inside a laptop or phone so the device itself can prove its identity to an organization.
Each form has its own tools and conventions, but the same questions apply to all of them: where the private key lives, how it is backed up, and how it can be revoked if lost.
Passkeys as Everyday Public Key Credentials
For most consumers, passkeys are the first public key credential they use knowingly. When you create a passkey, your device generates a new key pair just for that website or app and registers the public key with it. Signing in then requires your device and usually a fingerprint, face scan or PIN.
Passkeys come in two broad varieties. Synced passkeys are backed up through a platform account and appear on all your signed-in devices, which makes them convenient and recoverable. Device-bound passkeys stay on one piece of hardware, such as a security key, offering tighter control but requiring careful backup planning.
Neither type is automatically better. Synced passkeys shift some trust to the account that performs the syncing, so that account needs strong protection of its own. Device-bound passkeys suit high-risk accounts and workplaces that need to know exactly which hardware holds each credential.
Where Private Keys Should Live
A private key stored as an ordinary file can be copied by malware, included in a careless backup or shared by mistake. Once copied, it works just as well for the thief as for the owner, and the owner may never notice that a duplicate exists.
Hardware protection reduces this risk. Smart cards, security keys, trusted platform modules in laptops and secure elements in phones are components designed to generate and use keys internally without ever exposing them. Requests go in and signatures come out, but the key itself stays inside.
When hardware is not available, software keys should at least be encrypted with a strong passphrase and stored only on devices you control. Developers should avoid placing private keys in source code, shared folders or messaging apps, where they tend to persist long after anyone remembers putting them there.
Automated secret scanning in code repositories is a useful safety net for development teams, catching accidentally committed keys before they spread further.
Backup, Sync and Recovery Trade-Offs
Strong key protection creates a practical dilemma. If a key can never leave its hardware, losing that hardware means losing the credential. If a key can be copied for backup, each copy is another place it could be stolen. Every design balances these two risks.
For hardware-bound credentials, the standard answer is not to back up the key but to register a second authenticator. A spare security key stored safely at home, or a second enrolled device, lets you regain access and then revoke the lost one without involving the service’s support team.
For synced credentials, recovery depends on the platform account that holds the backups. Review how that account itself is recovered, keep recovery codes somewhere safe and offline, and make sure the recovery phone number or email is current. A weak recovery path effectively becomes the weakest credential you own.
Key Rotation and Retirement
Keys should not live forever. Rotation means replacing a key pair with a new one on a planned schedule or after a suspected exposure. Retirement means making sure an old key can no longer be used anywhere. Both are easier when you keep a simple record of where each key is registered.
- Generate the new key pair on the device or hardware that will hold it.
- Register or certify the new public key with every service that relied on the old one.
- Confirm that logins and signatures work with the new key.
- Remove or revoke the old public key at each service, or ask the issuing authority to revoke its certificate.
- Securely delete any remaining copies of the old private key.
The fourth step is the one most often skipped. An old SSH key left on a server or an unrevoked certificate can remain usable for years, quietly preserving access that everyone believes ended long ago.
Privacy Properties of Public Key Credentials
Well-designed public key credentials can improve privacy. Passkeys create a separate key pair for each website, so two services cannot compare public keys to discover that the same person uses both. This avoids the tracking risk that comes from reusing one identifier everywhere.
Other designs work differently. A single certificate or SSH key used across many systems acts as a stable identifier that links activity together. Sometimes that linkage is intended, as in workplace auditing, but it is worth recognizing so you can choose separate keys where separation matters.
Some authenticators can provide attestation, which is a signed statement about the device model or manufacturer that created a key. Organizations use attestation to confirm that keys sit in approved hardware. Consumer services generally avoid requesting it, because it can reveal device details that are unnecessary for an ordinary login.
When reviewing any key-based system, ask which identifiers it exposes, to whom, and whether those identifiers could be combined to follow someone across unrelated services.
Mistakes That Weaken Key-Based Identity
The most common failure is treating a public key credential as a set-and-forget item. People register a key on a work server, change jobs or devices, and never remove it. Over time, organizations accumulate keys whose owners and purposes nobody can identify.
Another mistake is generating keys on shared or untrusted machines, or emailing private keys between colleagues to save time. Any copy made outside protected storage undermines every other control. Teams should treat a private key that has been shared as compromised and replace it promptly.
A third weakness lies in the binding step. If a service lets anyone add a new key to an account after a weak login, an attacker who briefly gains access can register their own key and keep returning. Services should require strong reauthentication and send notifications whenever a new key is added.
Building a Healthy Key Credential Routine
For personal use, adopt passkeys on important accounts where they are offered, register at least two authenticators for each critical account, and keep recovery codes offline. Review the list of registered devices and keys in your account settings a few times a year, removing anything you no longer recognize.
For teams, maintain an inventory that records each key or certificate, its owner, where it is registered and when it should be rotated. Prefer hardware-backed keys for administrators, automate renewal for machine credentials, and include key removal in every offboarding checklist.
Public key credentials are becoming the default way people and systems prove identity online. The cryptography is mature and reliable; what decides real-world security is the discipline around storing, binding and retiring keys. Building that discipline now pays off as more services move away from passwords.