YubiKey 5.4 vs 5.7+: what changed, and should you replace your key?

How does YubiKey firmware 5.4 differ from 5.7+, and is it worth replacing your key? The hardware looks identical from the outside: USB-A or USB-C, with or without NFC, and the same gold touch sensor. Inside, however, the differences between firmware 5.4.x and 5.7.x are substantial. Before going any further, there is one important point to understand.

We will first look at the features and capabilities added in 5.7. Then we will examine the EUCLEAK vulnerability and whether it is a good reason to replace an older key.

How many credentials can a YubiKey store?

Firmware 5.7 raises the storage limits substantially, as confirmed in Yubico’s official firmware 5.7 technical documentation. Here are the exact figures:

With firmware 5.4, you can hit the 25-passkey limit sooner than expected: email, GitHub, a password manager, work services, a VPN, and a few test accounts. You may have to remove older passkeys before adding new ones. With 5.7+, a single key can cover all of these accounts with plenty of capacity to spare. For developer account protection, see our guide to setting up two-factor authentication on GitHub with a YubiKey.

The OATH capacity—used for the TOTP codes you see in Yubico Authenticator—has also doubled. If you keep TOTP credentials on the key rather than in a phone app, the jump from 32 to 64 slots is significant.

PIN policy and CTAP 2.1 in YubiKey 5.7+

The minimum PIN length in firmware 5.7 is eight characters for FIDO2, PIV, and OpenPGP. In 5.4, it was six characters for FIDO2 and four for PIV and OpenPGP. PIN complexity checks based on NIST SP 800-63B are also enabled by default, so simple patterns such as 12345678 and repeated characters are rejected by the key itself.

Firmware 5.7 also brings CTAP 2.1 features such as Force PIN Change, which requires users to change the PIN at first use, and Minimum PIN Length. These features matter less for personal use, but they are useful when issuing keys to employees and enforcing a centralised PIN policy.

Firmware 5.7 also adds Unicode PIN support for PIV and OpenPGP. In technical terms, a PIN can contain Cyrillic letters, emoji, or ideographs, with each code point counted as one character. In practice, this is best avoided: entering such a PIN from an iOS keyboard on someone else’s laptop is hardly convenient. Still, the option is there.

Restricted NFC

On firmware 5.4.x, NFC is always enabled. On 5.7+, NFC remains disabled by default until the key has been inserted into a USB port at least once. NFC is activated after that first connection.

Why? If the key is stolen before its first USB connection—for example, from a bag in a café or a backpack on public transport—an attacker cannot reach it with an NFC reader. NFC simply does not work until you have connected the key over USB at least once.

It is not a revolutionary change, but it is a useful security default.

New PIV algorithms

The PIV module in firmware 5.7+ adds support for newer algorithms:

• RSA-3072 and RSA-4096 — on-device key generation and key import.
• Ed25519 — digital signatures using the Edwards25519 curve.
• X25519 — key exchange using Curve25519.

Firmware 5.4.x supports only RSA-2048 and the NIST P-256 and P-384 curves for keys generated on the device. If you want to generate an Ed25519 SSH key directly on the YubiKey, use Ed25519 for Git commit signing, or generate RSA-4096 keys, firmware 5.4 cannot do it.

Firmware 5.7+ also lets you move and delete PIV keys without performing a full PIV reset. This is useful when you need to preserve an old decryption key without disrupting a working configuration.

FIPS status of YubiKey firmware

This is an important detail for anyone working with government or corporate infrastructure subject to FIPS requirements. The current certification status is documented in Yubico’s official YubiKey 5 FIPS Series documentation.

• 5.4.x — the FIPS 140-2 certification for the YubiKey 5 FIPS Series moved to the Sunset List in May 2026. Keys in existing deployments may continue to be used.
• 5.7.4 — effective 22 May 2026, the YubiKey 5 FIPS Series was officially validated by NIST under FIPS 140-3 at Overall Security Level 2 and Physical Security Level 3.

All FIPS 140-2 certificates are scheduled to move to the Historical List on 22 September 2026. This does not disable keys that are already deployed; they will continue to work. For new deployments that must meet current FIPS requirements, however, the sensible choice is a YubiKey 5 FIPS Series device running firmware 5.7.4.

If you need a certified FIPS key for a new deployment, choose a YubiKey 5 FIPS Series device with firmware 5.7.4 and FIPS 140-3 validation. Firmware 5.4.x may still be relevant to previously approved or existing deployments, but it is no longer the preferred option for new purchases. Personal users and most non-corporate environments do not need FIPS certification.

The EUCLEAK vulnerability: should you be concerned?

In September 2024, NinjaLab researcher Thomas Roche disclosed EUCLEAK (CVE-2024-45678), a side-channel attack against the Infineon cryptographic library used by YubiKey 5 Series devices running firmware earlier than 5.7. The affected implementation had been in use for 14 years and had passed around 80 high-assurance Common Criteria certifications without the flaw being detected.

How it works. When you touch the key to approve a sign-in, the chip performs a mathematical operation using the private key and emits weak electromagnetic signals in the process. An EM probe placed directly against the casing can capture these signals. By analysing them, an attacker can recover the private key that was never supposed to leave the device. In practice, this makes it possible to clone the key without leaving visible damage to the casing.

What the attacker needs:

• Physical access to your YubiKey for several minutes. The key must be opened and the casing removed.
• Specialised side-channel equipment: an oscilloscope, an EM probe, and a workstation. The setup costs at least several thousand dollars.
• Expertise in side-channel cryptanalysis at the level of a dedicated security researcher.
• For FIDO2 with user verification, the attacker also needs your PIN or biometric factor.

This is not a scalable attack. It is targeted, expensive, and technically demanding. For most users, the practical risk remains limited. It becomes more relevant when the key protects genuinely critical accounts and an attacker can gain temporary physical access—for example, through a hotel safe, an unattended bag at the office, a customs inspection, or someone with a technical background and access to your workspace.

In firmware 5.7, Yubico replaced the third-party Infineon cryptographic library with its own implementation, which is not affected by EUCLEAK. Older keys cannot be patched because the vulnerable library is embedded in the secure element.

Example. A YubiKey 5C NFC running firmware 5.4.3 is used as the second factor for a work account with access to production servers and a GitHub organisation. You travel for work and leave the key in a hotel safe. That creates a plausible EUCLEAK threat scenario: a sufficiently motivated attacker could clone the key while you are attending a conference. Firmware 5.7+ removes this issue at the hardware level.

Should you replace your key because of EUCLEAK?

A simple rule in information security is to compare the cost of an attack with the value of what it could unlock. EUCLEAK is not a remote exploit. It is a physical, targeted, and expensive operation. The figures below put the risk into context.

Minimum attack budget:

• Equipment: approximately $11,000 for an oscilloscope, an EM probe, an amplifier, and a workstation.
• Expertise: a specialist experienced in side-channel cryptanalysis. There are relatively few such specialists, and their time is expensive.
• Physical access: the attacker must obtain your key without being noticed, open the enclosure, take measurements, and reassemble it. Alternatively, the attacker needs prolonged physical access to the key in laboratory conditions.
• Time and risk: the operation takes anywhere from several minutes to several hours and carries a risk of detection.

A realistic estimate for a single attack—including equipment, specialist time, and the logistics of gaining physical access—is roughly $15,000–$50,000, depending on the scenario.

An attack is economically worthwhile only when the accounts, systems, or assets protected by the key are worth several times more than the attack itself. If an attacker spends $30,000 to clone your key, they expect to gain substantially more.

When you probably do not need to worry

• You use YubiKey for 2FA on email, social media, GitHub, and similar services without a direct financial component. An attacker is unlikely to spend more than $15,000 to clone a key simply to access your Facebook account.
• You are an ordinary user with a typical set of accounts. EUCLEAK does not scale: every key must be attacked individually, manually, and with physical access.

When replacing the key makes sense

• The key protects an exchange account whose balance is substantially greater than the cost of the attack. If you hold a six-figure amount or more on Binance or another exchange, a targeted attack can become economically rational.
• The key is used to access production infrastructure, corporate secrets, financial systems, or anything else where a compromise could cost the organisation hundreds of thousands of dollars or more.
• You are a public figure, journalist, activist, or work in an environment where state or corporate espionage is a realistic threat rather than a hypothetical one.

Example 1. Suppose you use a YubiKey running firmware 5.4 as the second factor for Gmail, GitHub, and several work services. No financial accounts are protected by the key. Your EUCLEAK risk is close to zero: no one is likely to spend more than $15,000 to access these accounts.

Example 2. Suppose a YubiKey running firmware 5.4 protects a Binance account with a balance of more than $200,000. You travel frequently and leave the key in a hotel safe. In this case, the attack may be economically worthwhile for an adversary. Replacing the key with a 5.7+ model for $75 removes this risk entirely.

Which version should you choose today: YubiKey 5.4 or 5.7+?

For a new purchase, firmware 5.7+ is the clear choice. If you need a key for a regulated environment, choose a YubiKey 5 FIPS Series device with firmware 5.7.4, which is validated under FIPS 140-3. Buying a 5.4 FIPS key for a new deployment makes sense only for specific legacy or previously approved projects.

All new YubiKey 5 Series and Security Key Series devices sold since May 2024 ship with firmware 5.7.x. You can check the version in Yubico Authenticator: the key series and firmware version appear in the upper-left corner of the main screen after the key is connected.

YubiKey 5.4 vs 5.7: key differences at a glance

• Storage — 100 passkeys instead of 25 and 64 OATH credentials instead of 32. Total capacity increases from 83 to 190 credentials.
• PIN — an eight-character minimum, complexity checks enabled by default, CTAP 2.1 with Force PIN Change, and Unicode support.
• Restricted NFC — NFC remains disabled until the first USB connection.
• PIV algorithms — RSA-3072/4096, Ed25519, and X25519 were added. Keys can be moved and deleted without resetting the slot.
• FIPS — the FIPS 140-2 certification for firmware 5.4.x moved to the Sunset List in May 2026; the YubiKey 5 FIPS Series with firmware 5.7.4 has been validated under FIPS 140-3 since 22 May 2026.
• EUCLEAK (CVE-2024-45678) — YubiKey 5 Series devices running firmware earlier than 5.7 can theoretically be cloned through a side-channel attack requiring equipment worth approximately $11,000 or more. Firmware 5.7+ addresses the issue by switching to Yubico’s own cryptographic library. Replace the key if it protects high-value resources; otherwise, an urgent replacement is unnecessary.

YubiKey firmware cannot be updated. If you are buying a new key, choose one with firmware 5.7+ and you should not need to think about this again for years.