For Arduino
Updated: spaniakos 2015

This is an example of how to use SHA256 of this SHA library.
The text and keys can be either in HEX or String format.
The examples are from the FIPS 180-2 and RFC4231

to use String key it must be in the form of : uint8_t hmacKey2= (unsigned char)"0123456789:;<=>?@ABC";