# HEADER_PARTIAL_IV

> `const` **HEADER\_PARTIAL\_IV**: `6` = `6`

Defined in: [packages/filecoin-encryption-envelope/src/cose/constants.ts:51](https://github.com/FilOzone/synapse-sdk/blob/9ad84d812e1dd635b76420a7d9388555a04f31b6/packages/filecoin-encryption-envelope/src/cose/constants.ts#L51)

`Partial IV`, RFC 9052 §3.1. Forbidden in both content buckets.

Rejected rather than ignored, unlike an unknown label. Partial IV means
"rebuild the nonce from this fragment plus shared context", and `iv` is
always present here — so the pair gives two conflicting instructions for
the same nonce with no rule for which wins. Our seven-byte base nonce is
not Partial IV reconstruction either; the missing bytes are the chunk
index and last-chunk flag, not shared context.

A library decision, not an amendment: docs/tech-spec.md, "Library profile
decisions".