Why is secrecy a social need? How can a secret be communicated in writing, without running the risk that it may be eventually unveiled by an unwanted third party? Yet how can the message be made intelligible to the uninitiated? Why is cryptology an inevitable outgrowth of writing? In the era of information highways, how can the confidentiality of private correspondence and of business transactions, as well as of state secrets, be adequately protected? How can the individual's right to privacy be reconciled ...

Why is secrecy a social need? How can a secret be communicated in writing, without running the risk that it may be eventually unveiled by an unwanted third party? Yet how can the message be made intelligible to the uninitiated? Why is cryptology an inevitable outgrowth of writing? In the era of information highways, how can the confidentiality of private correspondence and of business transactions, as well as of state secrets, be adequately protected? How can the individual's right to privacy be reconciled with the maintenance of law and order?
Jacques Stern recounts the history of cryptology, from its early days as an arcane activity relegated to the hidden world of defence and diplomacy, to its present-day invasion of our daily lives, through microchips, cellular phones, electronic bank transfers, the Internet, etc. He demonstrates that cryptology and data processing are intimately linked, since both may be regarded as sciences of coding and decoding messages.
However, for the author the primary innovation is theoretical. Has cryptology grown from an unsophisticated `cottage industry' to become a major mathematical discipline? Following an examination of the notions of truth and proof, the author argues that the `science of secrecy' inevitably leads to a reconsideration of the theory of knowledge.
Jacques Stern is the director of the Laboratoire d'informatique at the Ecole Normale supérieure, where he also teaches. He is a lecturer at the Ecole polytechnique.