Cryptography is a branch of mathematics.
And like all mathematics, it involves numbers, equations, and logic. The result is broadly accessible, but many of the ideas it explains are misunderstood even by the technically trained, so it is a work that offers something to techs and managers as well as lay readers. Schneier surveys the threats, covering not just the full range of criminal attacks but also publicity attacks and attacks using the legal system. He categorises the attackers, who can include national intelligence organisations and the press as well as terrorists, insiders, lone criminals, and corporate spies. And he looks as the various kinds of security we need, among them privacy, anonymity, integrity, authenticity, and audit.