By 1975, hardware developments enabled cost reductions that brought cryptographic devices to remote cash dispensers and computer terminals, standardizing cryptographic systems in a way that required innovation. Because existing hardware enabled two strangers to communicate across a network, cryptographic systems needed to enable those strangers to communicate securely and easily. At the time, symmetric key encryption established a shared secret between parties using a courier or an expensive private channel. This expensive, inefficient key distribution system did not empower two physical strangers to email one another. With the emergence of email, not only did key distribution need to simplify, but the authentication of electronic mail needed to equal that of physical mail. Signatures authenticated physical mail, and digital signatures could do the same for email. The desire to implement secure, authentic, and easy communication between strangers incited a dialogue between mathematicians across the United States. Ralph Merkle was the first to propose the concept of a public-key cryptosystem in which all information sent over a channel is public, but an eavesdropper must expend an exponentially larger amount of work than the secure communicators to read a message, making it statistically infeasible for the eavesdropper to decrypt. Merkle continued to work with Whitfield Diffie and Martin Hellman to establish the the Diffie-Hellman (D-H) key exchange in 1976, a non-authenticated key agreement protocol. Although the D-H key exchange was non-authenticated, it established the foundation for many authenticated protocols including RSA. Ron Rivest (an editor on Merkle’s original paper), Adi Shamir, and Leonard Adleman published a method for public-key cryptosystems and obtaining digital signatures 1977. Merkle, Diffie, Hellman, and the RSA team took each other’s courses and read each other’s papers, developing a dialogue in their work that optimized the work of their counterparts. Their dialogue was not only a form of collaboration, but it was communication that led to cryptosystems mimicking real systems. Because public-key encryption made email feel like physical mail or talking on the phone, except faster and easier, public-key cryptosystems became the most sustainable method of key exchange.

