Fix: Change OKP JWK thumbprint to use crv/kty/x, not RSA's kty/n/x - #26
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Fix: Change OKP JWK thumbprint to use crv/kty/x, not RSA's kty/n/x#26nomadium wants to merge 1 commit into
nomadium wants to merge 1 commit into
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OKP_PUBLIC_KEY_ELEMENTS was copy-pasted from an RSA-shaped element
list (kty, n, x). "n" is the RSA modulus and never applies to OKP
(Ed25519) keys, so it always serialized as null; "crv" is required by
RFC 8037 but was missing entirely.
This list feeds JWK::OKP#members, which JWT::JWK::Thumbprint (RFC
7638) uses directly to compute the SHA-256 thumbprint, and jwt's
default kid_generator (:key_digest) uses that thumbprint as the
auto-generated "kid" for every key this gem creates. As a result,
every kid produced by this gem is computed over the wrong JSON
({"kty":"OKP","n":null,"x":"..."}) instead of the RFC 7638-correct
{"crv":"Ed25519","kty":"OKP","x":"..."}, so it never matches the
thumbprint a spec-compliant verifier computes for the same key.
Add a regression test pinned to the published RFC 8037 Appendix A.3
thumbprint test vector.
nomadium
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Aug 10, 2026
…sa's kid
jwt-eddsa (<= 0.9.0) computes JWK::OKP's thumbprint over the wrong
members ({kty, n, x} instead of the RFC 8037-correct {crv, kty, x}),
so the Web Bot Auth `keyid` derived from it never matched what a
spec-compliant verifier expects.
Add Linzer::JWS::Key#jwk_thumbprint and use it instead, so Linzer
is correct independent of jwt/ruby-jwt-eddsa#26.
anakinj
changed the title
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Description
Fix OKP JWK thumbprint: use crv/kty/x, not RSA's kty/n/x
OKP_PUBLIC_KEY_ELEMENTS was copy-pasted from an RSA-shaped element list (kty, n, x). "n" is the RSA modulus and never applies to OKP (Ed25519) keys, so it always serialized as null; "crv" is required by RFC 8037 but was missing entirely.
This list feeds
JWK::OKP#members, whichJWT::JWK::Thumbprint(RFC 7638) uses directly to compute the SHA-256 thumbprint, and jwt's default kid_generator (:key_digest) uses that thumbprint as the auto-generated "kid" for every key this gem creates. As a result, every kid produced by this gem is computed over the wrong JSON ({"kty":"OKP","n":null,"x":"..."}) instead of the RFC 7638-correct{"crv":"Ed25519","kty":"OKP","x":"..."}, so it never matches the thumbprint a spec-compliant verifier computes for the same key.Add a regression test pinned to the published RFC 8037 Appendix A.3 thumbprint test vector.
Checklist
Before the PR can be merged be sure the following are checked:
Notes
I stumbled upon this issue after investigating why JWK keys generated by Linzer gem (which depends on jwt-eddsa) and associated HTTP message signatures were failing verification at a CloudFlare debug utility website.