Add Description of cryptography being used for OTP

[ntelfer]

We are using one time pads and signatures to encrypt private keys. We use a cryptographically secure pseudo-random number generator(CSPRNG) to generate a 128 bit seed. The seed is then stretched to create the one time pad. The pad is then XOR'd with the data to encrypt it. Finally the data is signed to make it tamper proof. Didery will only allow a signature to be added to the public store if the signature validates.