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 those who can see the encrypted data. Encryption and decryption require the use of some secret information, usually referred to as a key. Depending on the encryption mechanism used, the same key might be used for both encryption and decryption, while for other mechanisms, the keys used for encryption and decryption might be different. But today s cryptography is more than secret writing, more than encryption and decryption.
Authentication is as fundamental a part of our lives as privacy.
We use authentication though out our everyday life, for instance when we sign our name to some document. As we move to a world where our decisions and agreements are communicated electronically, we need to replicate these procedures. Cryptography provides mechanisms for such procedures. 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. But the field of cryptography contains even more when we include some of the things cryptography enables us to do.