Is this a reasonable way to implement 'remember me' functionality

Question

If a user logs into the site, and says \'remember me\', we get the unique identifier for the user, encrypt this with RijndaelManaged with a keysize of 256 and place this in

Answer 1

How important is the information that is being remembered? If it's not going to be anything very personal or important, just put a GUID in the cookie.

Including the IP address in the calculation is probably a bad idea, as it would make users using public networks be instantly forgotten.

Using brute force to find GUIDs is ridiculous, as there are 2¹²⁸ possibilities.