Key Exchange Protocols

Protocols that let two parties agree on a shared secret key over a channel that others can watch. The Diffie-Hellman key exchange, published in 1976, gets its security from the difficulty of the discrete logarithm problem, and its elliptic-curve form, ECDH, achieves similar security with much shorter keys. The shared key is then used with a symmetric cipher to protect the messages that follow, which is how secure web connections and many messaging systems begin.