A physical **security key** adds a very strong layer of protection to your online accounts. Compared to [authenticator apps](multi-factor-authentication.md), the FIDO2 security key protocol is immune to phishing, and cannot be compromised without physical possession of the key itself. Many services support FIDO2/WebAuthn as a multi-factor authentication option for securing your account, and some services allow you to use a security key as a strong single-factor authenticator with passwordless authentication.
## Yubico Security Key
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The **Yubico Security Key** series is the most cost-effective hardware security key with FIDO Level 2 certification. It supports FIDO2/WebAuthn and FIDO U2F, and works out of the box with most services that support a security key as a second factor, as well as many password managers.
These keys are available in both USB-C and USB-A variants, and both options support NFC for use with a mobile device as well.
This key provides only basic FIDO2 functionality, but for most people that is all you will need. Some notable features the Security Key series does **not** have include:
If you need any of those features, you should consider their higher-end [YubiKey](#yubikey) of products instead.
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<pclass="admonition-title">Warning</p>
The firmware of Yubico's Security Keys is not updatable. If you want features in newer firmware versions, or if there is a vulnerability in the firmware version you are using, you would need to purchase a new key.
The **YubiKey** series from Yubico are among the most popular security keys. The YubiKey 5 Series has a wide range of features such as: [Universal 2nd Factor (U2F)](https://en.wikipedia.org/wiki/Universal_2nd_Factor), [FIDO2 and WebAuthn](basics/multi-factor-authentication.md#fido-fast-identity-online), [Yubico OTP](basics/multi-factor-authentication.md#yubico-otp), [Personal Identity Verification (PIV)](https://developers.yubico.com/PIV), [OpenPGP](https://developers.yubico.com/PGP), [TOTP and HOTP](https://developers.yubico.com/OATH) authentication.
The [comparison table](https://yubico.com/store/compare) shows the features and how the YubiKeys compare to each other and to Yubico's [Security Key](#yubico-security-key) series. One of the benefits of the YubiKey series is that one key can do almost everything you could expect from a hardware security key. We encourage you to take their [quiz](https://yubico.com/quiz) before purchasing in order to make sure you make the right choice.
The Yubikey 5 series has FIDO Level 1 certification, which is the most common. However, some governments or other organizations may require a key with Level 2 certification, in which case you'll have to purchase a [Yubikey 5 **FIPS** series](https://yubico.com/products/yubikey-fips) key, or a [Yubico Security Key](#yubico-security-key). Most people do not have to worry about this distinction.
YubiKeys can be programmed using the [YubiKey Manager](https://yubico.com/support/download/yubikey-manager) or [YubiKey Personalization Tools](https://yubico.com/support/download/yubikey-personalization-tools). For managing TOTP codes, you can use the [Yubico Authenticator](https://yubico.com/products/yubico-authenticator). All of Yubico's clients are open source.
For models which support HOTP and TOTP, there are 2 slots in the OTP interface which could be used for HOTP and 32 slots to store TOTP secrets. These secrets are stored encrypted on the key and never expose them to the devices they are plugged into. Once a seed (shared secret) is given to the Yubico Authenticator, it will only give out the six-digit codes, but never the seed. This security model helps limit what an attacker can do if they compromise one of the devices running the Yubico Authenticator and make the YubiKey resistant to a physical attacker.
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<pclass="admonition-title">Warning</p>
The firmware of YubiKey is not updatable. If you want features in newer firmware versions, or if there is a vulnerability in the firmware version you are using, you would need to purchase a new key.
**Nitrokey** has a security key capable of [FIDO2 and WebAuthn](basics/multi-factor-authentication.md#fido-fast-identity-online) called the **Nitrokey FIDO2**. For PGP support, you need to purchase one of their other keys such as the **Nitrokey Start**, **Nitrokey Pro 2** or the **Nitrokey Storage 2**.
The [comparison table](https://nitrokey.com/#comparison) shows the features and how the Nitrokey models compare. The **Nitrokey 3** listed will have a combined feature set.
Nitrokey models can be configured using the [Nitrokey app](https://nitrokey.com/download).
For the models which support HOTP and TOTP, there are 3 slots for HOTP and 15 for TOTP. Some Nitrokeys can act as a password manager. They can store 16 different credentials and encrypt them using the same password as the OpenPGP interface.
<divclass="admonition warning"markdown>
<pclass="admonition-title">Warning</p>
While Nitrokeys do not release the HOTP/TOTP secrets to the device they are plugged into, the HOTP and TOTP storage is **not** encrypted and is vulnerable to physical attacks. If you are looking to store HOTP or TOTP secrets, we highly recommend that you use a YubiKey instead.
</div>
<divclass="admonition warning"markdown>
<pclass="admonition-title">Warning</p>
Resetting the OpenPGP interface on a Nitrokey will also make the password database [inaccessible](https://docs.nitrokey.com/pro/linux/factory-reset).
</div>
## Criteria
**Please note we are not affiliated with any of the projects we recommend.** In addition to [our standard criteria](about/criteria.md), we have developed a clear set of requirements to allow us to provide objective recommendations. We suggest you familiarize yourself with this list before choosing to use a project, and conduct your own research to ensure it's the right choice for you.
### Minimum Requirements
- Must use high quality, tamper resistant hardware security modules.
- Must support the latest FIDO2 specification.
- Must not allow private key extraction.
- Devices which cost over $35 must support handling OpenPGP and S/MIME.
### Best-Case
Our best-case criteria represents what we would like to see from the perfect project in this category. Our recommendations may not include any or all of this functionality, but those which do may rank higher than others on this page.
