Essay:What is cryptography?

From CRYPTUTOR

Cryptography is ...

• ... an approach to understanding problems in security. These include classical problems like communication and authentication, but also more modern ones such as zero-knowledge proofs and multi-party computation. The unifying theme of security among these problems is that of strictly controlling what information is available to parties who interact with each other to accomplish some task, even in the presence of malicious adversaries.

• ... an approach to these security problems from a mathematical point-of-view. It focuses on formal mathematical models and definitions of security which allow us to prove statements about the security properties of systems.

• ... based on computational complexity. Most notably, cryptography uses complexity-theoretic notions such as reductions and computationally hard problems. Adversaries are often modeled as resource-bounded computer programs. Security proofs in cryptography often reduce a problem that is computationally hard for such an adversary to the problem of violating a system's security guarantee.