What if Public-Key Cryptography Didn Exist?
Public-key cryptography makes it practical and convenient for parties to set up secure communications with each other over the Internet without any other form of prior contact. Authenticating the identity of each party to the other still does require some setup, but this can be done ahead of time without even directly involving the two parties themselves, by the use of certificates made using digital signatures, another function that public-key cryptography makes possible. Thus, your browser contains the information that “Key XXXX really is the public key of this digital signature company”, and when you order something from a company, that company first provides your browser with a message, enciphered in the secret key corresponding to the public key XXXX, which states that “Key YYYY is really the public key of this merchant, whose website is here”. So the prior contact between the digital signature company and the company that wrote the web browser you used is enough to ensure that wh
