Cryptobench

wycheproof-ed25519-invalid-encoding

EdDSA: Invalid encoding

The test vector contains a signature with an invalid encoding of the values. The vector checks that invalid encodings are not accepted. For the vectors that modify the encoding of R, S has been recomputed so that the hash matches the modified R and the R recovered from S and the hash equals the original R. Such vectors are accepted only by verifiers that decode R leniently or that compare R to the recovered R incompletely.

REJECT

Your service should reject this one.

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

Accepting such signatures means the encoding of a signature is not unique. A holder of the private key can generate multiple distinct signatures for the same message, and different verifiers can disagree about which signatures are valid. Demonstrated by 22 test vectors in Project Wycheproof.

Provenance

Kind
hardeningDefensible practice with no normative source. Judge it for yourself.
Source
wycheproof
Clause
RFC 8032 §5.1
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.