2.1.7.15 Signatures Stream (_signatures)
The Signatures Stream is specified in [MS-OFFCRYPTO] section 2.5.1.
The name of this stream MUST be "_signatures". A file MUST contain at most one Signatures Stream<1>.
When generating the Signature value, as specified in [MS-OFFCRYPTO] section 2.5.1.5, the record data, as specified in section 2.1.4, of the WriteAccess record (section 2.4.349) in the Globals Substream (section 2.1.7.20.3) is skipped.