The Network-Layer Encryption feature was introduced in Cisco IOS 11.2. New session keys are generated on a configurable basis. Encryption policy is set by crypto-maps that use extended IP Access Lists to define which network, subnet, host, or protocol pairs are to be encrypted between routers. The field of cryptography is concerned with keeping communications private. The protection of sensitive communications has been the emphasis of cryptography throughout much of its history.
Encryption is the transformation of data into some unreadable form.
Its purpose is to ensure privacy by keeping the information hidden from anyone for whom it is not intended, even if they can see the encrypted data. A digital signature binds a document to the possessor of a particular key, while a digital timestamp binds a document to its creation at a particular time. While modern cryptography is growing increasingly diverse, cryptography is fundamentally based on problems that are difficult to solve. As the field of cryptography has advanced, the dividing lines for what is and what is not cryptography have become blurred. Cryptography today might be summed up as the study of techniques and applications that depend on the existence of mathemetical problems that are difficult to solve.