# HEADER_PLAINTEXT_LENGTH

> `const` **HEADER\_PLAINTEXT\_LENGTH**: `-65789` = `-65789`

Defined in: [packages/filecoin-encryption-envelope/src/cose/constants.ts:73](https://github.com/FilOzone/synapse-sdk/blob/9ad84d812e1dd635b76420a7d9388555a04f31b6/packages/filecoin-encryption-envelope/src/cose/constants.ts#L73)

`plaintext_length`, private use (RFC 9052 §3.1). Optional; written only
when the caller knew the content length before the envelope was emitted.

Being protected is what makes it a truncation check: an attacker can
neither edit it to match a short object nor strip it to escape the
comparison, since both change the AAD and fail every chunk tag.

Do not renumber this to `-65791`: see docs/tech-spec.md,
"`plaintext_length` and truncation".