For more information about making data tamper-proof using HMACs see the paper "Dos and Don'ts of Client Authentication on the Web" by Kevin Fu et al. [1]. I've

For more information about making data tamper-proof using HMACs see the paper "Dos and Don'ts of Client Authentication on the Web" by Kevin Fu et al. [1]. I've implemented the "FuCookie" and I use it everywhere. [1] http://pdos.csail.mit.edu/papers/webauth:tr.pdf http://pdos.csail.mit.edu/papers/webauth:tr.pdf