# 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/9ad84d812e1dd635b76420a7d9388555a04f31b6/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).