Decode and validate an ISO mdoc (CBOR-encoded mobile credential) response
domain: iso.org · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
An mdoc response (DeviceResponse) is CBOR-encoded; use a CBOR library to decode it — the top-level structure contains a version field and a documents array.
Each document contains docType (e.g. 'org.iso.18013.5.1.mDL'), issuerSigned, and deviceSigned sections.
issuerSigned.issuerAuth is a COSE_Sign1 structure; decode it to get the MobileSecurityObject (MSO), which contains the signed document type, validity period, device key, and a digest map of the data elements.
issuerSigned.nameSpaces contains the actual data element values as IssuerSignedItems; each item has a random salt, data element identifier, and value — compute SHA-256(bstr(IssuerSignedItem)) and compare against the digest in the MSO to verify integrity.
deviceSigned.deviceAuth is a COSE_Sign1 or COSE_Mac0; verify it using the device public key from the MSO to confirm the credential is presented by the legitimate holder device.
Known gotchas
CBOR has multiple encoding variants; mdoc uses deterministic CBOR (RFC 7049 canonical form); a library that accepts non-canonical CBOR may silently accept malformed mdocs.
The MSO digest map uses a hash of the bstr-wrapped IssuerSignedItem CBOR encoding, not the raw value — hashing the wrong bytes is a common verification bug.
Validity period in the MSO (validFrom, validUntil) must be checked against the current time; an expired MSO should be rejected even if the signatures are valid.
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