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CodeQL alert #21 (go/weak-sensitive-data-hashing, severity: High) flagged the sha256.Sum256(signingInput) call in verifyES256 at internal/scep/intune/challenge.go:380 as 'weak hashing of sensitive data', suggesting PBKDF2/Argon2/bcrypt instead. This is a CodeQL false positive. The CodeQL query triggers when SHA-256 is used near *x509.Certificate (the trust pool) and infers 'this might be password hashing.' But the actual context is JWS signature verification: - verifyRS256 implements RFC 7518 §3.3 — 'RSASSA-PKCS1-v1_5 using SHA-256'. SHA-256 is spec-mandated. - verifyES256 implements RFC 7518 §3.4 — 'ECDSA using P-256 and SHA-256'. SHA-256 is spec-mandated. - The signing input is the JWS protected header + payload (base64url-encoded). It is a public, well-known message with full 256-bit-entropy contributed by signer-controlled nonces + timestamps + device claims — the opposite of a low-entropy password. - The output is verified against an asymmetric signature (rsa.VerifyPKCS1v15 / ecdsa.Verify), not compared to a pre-computed hash digest. This is signature verification, not password hashing. - Switching to PBKDF2 / Argon2 / bcrypt would BREAK every Intune Connector signed challenge — Microsoft + every spec-conforming JWS library will only verify against SHA-256 for these algs. Fix: add explicit RFC-citing comment blocks above each verifier function explaining the JWS context + add //nolint:gosec annotations on the sha256.Sum256 calls so CodeQL recognizes the suppression rationale at the call site. The annotation cites the specific RFC clause (7518 §3.3 / §3.4) so a future security reviewer can re-derive the conclusion without re-reading the alert. The algorithm allowlist itself stays defensively narrow: - alg="RS256" → verifyRS256 with SHA-256 - alg="ES256" → verifyES256 with SHA-256 - alg="none" → explicit reject (RFC 7515 §3.6 attack vector) - any other alg → reject as unsupported Pinned by existing tests: - TestValidateChallenge_HappyPath_RS256 - TestValidateChallenge_HappyPath_ES256_FixedWidth - TestValidateChallenge_HappyPath_ES256_DER - TestValidateChallenge_AlgNoneRejected - TestValidateChallenge_UnsupportedAlg The happy-path tests would fail if the verifiers switched to any non-SHA-256 digest — the alg allowlist makes the SHA-256 dependency load-bearing, which the existing test suite already proves. Verified locally: gofmt: clean. go vet ./internal/scep/intune/...: exit 0. go test -short -count=1 ./internal/scep/intune/...: PASS (every existing challenge_test.go subtest still green). Reference: https://github.com/certctl-io/certctl/security/code-scanning/21 Closes CodeQL alert #21 as a documented false positive — the //nolint annotations + RFC-citing comments are the load-bearing suppression. Operators can dismiss the alert in the GitHub UI with reason 'Won't fix' citing this commit.