Cryptobench

wycheproof-dsa-modified-signature

DSA: Modified signature

The test vector contains an invalid signature that was generated from a valid signature by modifying it.

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.

Without further analysis it is unclear if the modification can be used to forge signatures. Demonstrated by 189 test vectors across 4 vector documents in Project Wycheproof.

Provenance

Kind
hardeningDefensible practice with no normative source. Judge it for yourself.
Source
wycheproof
Clause
FIPS 186-4 §4
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.