MVIII. Techniques of Secrecy

A whispered voice, a closed door, a sealed envelope –- these are all familiar, everyday techniques and technologies by means of which people routinely seek to maintain their secrets and preserve a measure of personal privacy.

Cryptography, the art of making ciphers and codes, provides an additional array of powerful techniques to accomplish the same purposes under different circumstances. Cryptographic techniques attempt to protect information from unwanted scrutiny by transforming or encrypting it into an otherwise unintelligible form called a cipher-text. This cipher-text ideally cannot be deciphered back into an intelligible plain-text without the use of a key to which only those who are the intended recipients of the information have access. The use of ever more powerful computers to facilitate the construction and application of encryption algorithms and keys has made the effort to discern the original plain-text from an encrypted cipher-text without recourse to its proper key incomparably more difficult than has been the case historically. This kind of code-breaking is called cryptanalysis. Cryptology is a more general term encompassing both cryptography and cryptanalysis.

There are two basic kinds of encryption scheme in contemporary cryptography, symmetric and asymmetric systems. In classic symmetric encryption or secret key cryptology, messages are enciphered and deciphered by recourse to a secret key available to all (but only) the relevant parties to a transaction. Such systems are called symmetrical simply because both the processes of scrambling text into cipher-text and descrambling cipher-text back to plain-text require access to exactly the same information. The obvious difficulty with such symmetric systems is their reliance on a secret key that cannot always itself be distributed with ease or comparable security. This dilemma constituted in fact one of the definitive quandaries of cryptography for centuries, but it was overcome in a series of breakthroughs in relatively recent history. The result is called asymmetric or public key cryptology.

Public key encryption, as we know it, was devised by 1976 by Whitfield Diffie (of whom Simon Singh writes: “In hindsight, he was the first cypherpunk” ), Martin Hellman, and Ralph Merkle. Asymmetric encryption schemes require not one but two keys, a public or published key available to everyone as well as a secret key known, as usual, only by deliberately chosen individuals, and often known only by a single person and never revealed to anyone else at all. These two coded keys stand in the unique mathematical relation to one another that once a text has been scrambled into cipher-text by means of the public key, it can be subsequently descrambled from cipher-text back into intelligible plan-text only by means of the private or secret key associated with it. With this breakthrough the dilemma of insecure key distribution was solved, and it became possible even for parties whose identities are secrets kept from one another to communicate and conduct transactions with one another in a way that was likewise perfectly secret to anyone but themselves.

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