[Phemist]

Yes, as this blog post doesn't mention it, the "password key" is specifically derived from your Date of Birth, the document's Date of Expiry and the Document Number. For the specimen document in the blog post these values are respectively 740812 (YYMMDD), 120415 (YYMMDD) and L898902C3. They are contained in both the MRZ and the VIZ (Visual Inspection Zone).

Considering the Date of Birth and Date of Expiry are necessarily limited in entropy, one should take care in protecting their Document Number as it is the greatest source of entropy for the derived "password key".