FA-76625 / Email MIME structure / Member archive

Validate the structure of a multipart/signed entity: micalg family · case 05

S/MIME signatures with a non-pgp micalg are rejected, or pgp signatures announce S/MIME algorithms unnoticed.

Member previewVariant 5 · 3 implementations · 9 checks per implementation

Case contract

Parameter names are case-insensitive. Findings, in order: not-signed (and stop) unless type is multipart/signed; missing-protocol; part-count (and stop) unless exactly two parts; protocol-mismatch when a protocol exists and the second part's type differs from it (case-insensitive); missing-micalg, or micalg-mismatch when a protocol exists and the micalg family disagrees (pgp-* exactly when the protocol is application/pgp-signature); unprotected-8bit when the signed first part uses 8bit or binary transfer encoding.

Why this case matters

Signed mail is only verifiable when its structure is exact; lax checks accept tampered or unverifiable messages.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
S/MIME signature	`["micalg-mismatch"]`	`[]`	Failed

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