micalg

MIME parameter announcing the hash algorithm of an AS2/S/MIME signed message.

Definition

micalg lets a receiver start the first hashing pass before even reading the signature part. In S/MIME 4.0 the registered values are sha-256, sha-384, sha-512 (plus the legacy sha-1). The same algorithm value governs the MIC returned in an AS2 signed MDN receipt; a mis-negotiated micalg causes a MIC verification failure.

Origin

Introduced by RFC 1847, with values specified by RFC 5751 / RFC 8551 (S/MIME) and used by RFC 4130 (AS2-MDN).

Example in context

protocol="application/pkcs7-signature"; micalg=sha-256

Related terms

• multipart/signed — carrier content type.