Cryptobench

wycheproof-aes-gcm-small-iv

AES-GCM: Small iv

GCM leaks the authentication key if the same IV is used twice. Hence short IV sizes are typically discouraged or generated with a special construction such as the one described in Section 8.2 of NIST SP 800-38d. Some libraries may reject small IV sizes.

ACCEPT

Your service should accept this one.

Stated as the outcome to assert against, so a suite compares with this rather than hardcoding a result and getting it backwards.

GCM leaks the authentication key if the same IV is used twice. Hence short IV sizes are typically discouraged or generated with a special construction such as the one described in Section 8.2 of NIST SP 800-38d. Some libraries may reject small IV sizes. Demonstrated by 36 test vectors in Project Wycheproof.

Provenance

Kind
hardeningDefensible practice with no normative source. Judge it for yourself.
Source
wycheproof
Clause
NIST SP 800-38D
CVE
none
Weakness
none
Produce this on the benchTake a token apart

Test keys only. Nothing here is a statement about any particular service: the expected outcome above is what an application ought to do, not evidence that yours does.

Reference

URL or embedded key?

Your app needs the public key to check a token. It can fetch it from a URL at runtime, or carry it as a file. Both are normal. The trade is always the same one: who controls rotation.

Fetch from the URLEmbed the key
RotationAutomatic on next fetchNeeds a redeploy
NetworkDepends on the URLNone
TrustWhatever the endpoint servesPinned to one key
SuitsA signer that rotates keysOffline, air-gapped, or pinned

Use the URL when the signer rotates its keys, which is what every identity provider does. That is why it became the norm, and it is usually a one-line config change.

Embed the key when you cannot make a network call while checking a token, or when you want your app pinned to one key so a compromised endpoint could not introduce another. Export the PEM from the Keysets tab.

One catch worth knowing: Spring Boot's public-key-location only loads RSA keys. An ES256 or EdDSA key needs a custom decoder, or the URL.