so here is the crypto lab, and in here we do a variety of software testing on both encryption standards and operating systems and anything else that might be security-sensitive. here is an antique from 1980, older than i am. this implements the n.i.s.t. data encryption algorithm. we don't need this machine because any desktop pc can do the work that this used to do. because the algorithm implemented by this machine is a secret-key algorithm, in order to use it, you need sender and recipient to share a secret, which in general is not true of any two computers that you pick randomly communicating using the internet. this is where public-key cryptography comes in. public-key cryptography is a product of prime numbers, n=pq. in addition to n will be a public exponent, e. with public-key algorithms, only the recipient needs to know a secret, and the recipient just needs to securely get the public key, which explains to the sender how to encrypt data so only the recipient can read it. e can be set pretty much to anything as long as it doesn't divide p-1 or q-1. 3 is a common choice, 17 is com