Validate an eMRTD chip's Passive Authentication signature chain against the ICAO Public Key Directory (PKD) to establish issuer trust, not just internal signature consistency
domain: icao.int · 6 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
After reading the chip's Document Security Object (SOD) via NFC, extract the Document Signer Certificate (DSC) used to sign the SOD
Fetch or maintain a synced copy of the issuing country's Country Signing CA (CSCA) certificates and Certificate Revocation Lists from the ICAO PKD
Verify the DSC chains up to a trusted CSCA certificate for the document's issuing country, rather than accepting any internally-consistent signature
Check the DSC and CSCA against current revocation lists to reject documents signed with a since-revoked certificate
Recompute data group hashes from the chip and compare them to the hash values inside the signed SOD to detect any post-issuance tampering
Reject or flag for manual review any document whose signer certificate cannot be chained to a known, non-revoked CSCA in the PKD
Known gotchas
Verifying only that the SOD's signature is internally valid (signature matches the DSC) without chaining to a trusted CSCA in the PKD leaves you exposed to documents signed by an unknown or fraudulent issuer — internal consistency is not the same as trust
Not all issuing countries participate fully in the ICAO PKD or publish timely CRL updates, so a legitimate document can fail trust-chain validation due to PKD data gaps rather than actual fraud — plan a manual-review fallback for that case
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