Should hidden field information always be encrypted?

A question based on a comment made here:

storing user detail ... session vs cache !

Summary: I mentioned a technique I've used where I populate a model and use hidden fields to keep and pass back that information; Viewstate on the cheap. Simon Halsey said that the information should be encrypted or hashed so it is not tampered with. I'm thinking the added complexity of hashing it is just a f开发者_运维百科orm of YAGNI.

I can see that for sensitive information, definitely, but is this a good rule of thumb in general? What am I missing?

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I actually have an attribute to do this (something similar) and speak about this exact thing in a security presentation. Yes - you should hash a copy of the value... encrypting it is up to you. if you encrypt it you get no model binding but is more open to attack, although a hash check helps. I'll post the code shortly for it and update this post. Who would ever think Viewstate helped with security : )

but to answer your question - you can encrypt it, but you need a way to at least validate it on the server side, so I hash a value and hash the posted value and then compare hashes in the attribute. encrypting can help - but then you need to implement either your own model binder or manually handle those values

The rule of thumb would be generally for any values that could be maliciously overwritten to attack your data - then you want some protection/validation on those fields. you could compare server side against what you know is a valid option for them (a form of whitelisting) but then you have the same form of rules duplicated on loading the data and on saving the data and that gets a bit messy at times, unless its as simple as limiting a user's get/update to a single userId.

What I mean is.. if you are updating say a user's record. Generally the main thing that matters for security is that the userId is not changed by the user to update a record that isn't theirs. The logic on get/save is easy "where o.UserId == userId"

However in complex role based security the logic becomes trickier and is not as clean to limit record updates like this. In those cases you can really take advantage of encrypted/hashed fields. I always hash the specific fields uses for update. Sure - they can be forged with other valid hashed fields from a previous request, but the scope of potential damage is significantly more limited this way.