A comment on another question made me wonder about something:


  Assume you're on a rather constrained platform &mdash; say, a low-end embedded device &mdash; with no built-in crypto capabilities, but you do have access to a simple stream cipher; say, RC4 or one of the eSTREAM ciphers.  What other crypto primitives can you build out of that stream cipher?  In particular, are there any practical ways to build a cryptographic hash function and/or a MAC out of just a stream cipher?


We already have questions about turning a hash into a stream cipher and about turning a stream cipher into a block cipher, but this particular transformation doesn't seem to have been covered yet.

Obviously, if the platform constraints permit it, one could ignore the stream cipher and just implement a standard hash function from the ground up.  What I'm wondering is whether having the stream cipher available might let one do better than that in terms of code size, memory usage and/or speed.

While a construction that treats the stream cipher as a black box would be nice, schemes that only use parts of the stream cipher (like RC4-Hash, which, alas, has practical collision attacks) would be interesting too, at least if they're simple enough.


Question: Should I use cement board or green board behind the walls of a neo angle shower?
Answer: I would always use cement board in the shower area.  I would extend the cement board to where you shower unit will cover.  You can go past that point just plaster with a nice joint compound, like durabond to join to the rest of the plaster board for a permanent bond. I typically do not use green board unless you expect the wall can get wet, like a basement.  My bathroom is upstairs and my house would wash away before those walls got wet, therefore regular board is fine.