I disagree. It's a well known method of sanity checking serialized data, and it's used by lots and lots of file formats and "over the wire" data formats. It's

I disagree. It's a well known method of sanity checking serialized data, and it's used by lots and lots of file formats and "over the wire" data formats. It's not really a security feature, and it doesn't have to be a secret value. It also doesn't mean you shouldn't sanity check the other data fields. The sole purpose is to quickly rule out data that's blatantly incorrect.