# HEADER_IV

> `const` **HEADER\_IV**: `5` = `5`

Defined in: [packages/filecoin-encryption-envelope/src/cose/constants.ts:37](https://github.com/FilOzone/synapse-sdk/blob/bc8a4b093324ccef9b407251fcf4e91823c6f599/packages/filecoin-encryption-envelope/src/cose/constants.ts#L37)

`iv`, RFC 9052 §3.1: a 12-byte nonce (scheme 1) or a 7-byte base nonce
(chunked).

COSE permits either bucket. This profile requires the **protected** one so
the IV is covered by the content AAD, and rejects the label in the
unprotected map (FIP amendment 3).