Why cryptography: confidentiality, integrity, authentication, non-repudiation; data at rest, in transit, in use

Cryptography is the science of protecting information by transforming it with mathematical algorithms and secret values called keys. It is one of the few security controls that keeps working after other defenses fail: if an attacker steals an encrypted laptop or captures encrypted network traffic, the data is still protected as long as the keys are safe. Understanding what cryptography can and cannot do is the first step to choosing the right tool.