This is a trimmed-down version of Peter Knight's excellent Cryptosuite library for Arduino, supporting secure hashing and hashed message authentication using SHA-1 and HMAC-SHA-1. To help fit complex applications within the limited code space of the Arduino, this version strips out the SHA-256 functionality -- it wasn't required of our OAuth-driven code. If you specifically require this capability (and can afford the extra program space), download the original full version of the library here: https://github.com/Cathedrow/Cryptosuite The original also contains a test suite and further exposition on the use of hash functions. Installation: Make a 'libraries' directory with your Arduino sketches folder if you do not already have one. Rename this folder 'Sha' and move it into that directory. Restart Arduino IDE to rescan for new libraries.