Cryptography is any technique used for hiding data. It comes from the Greek words "crypto" meaning "hidden" and "graphy" meaning writing, so it's "hidden writing." Trust me, with a name like Ted Demopoulos I know Greek!
Cryptography is used for four basic purposes:
Confidentiality and integrity pertain to the data in a message, whereas
authentication pertains to the sender or creator of the message and the
recipient, and non-repudiation pertains to the sender or creator of
the message. We'll go into more detail on upcoming pages, but briefly:
Privacy/Confidentiality: Ensuring that data cannot be
revealed to unauthorized entities. This involves full encryption of the
user data. Those who can't decrypt the message see only
gibberish.
Integrity: Ensuring that data has not been modified or
corrupted. It is typically verified using cryptographic data
checksums, which is a less expensive operation than full encryption of
data. The data isn't secret - anyone can see/read it, but it can't be
modified without detection.
Authentication: Securely proving entities are who they
claim they are, so that they may trust each other. For example, a user
must trust a printer service before sending it confidential information
- a phony printer service could collect the information and transmit it
to a competitor.
Nonrepudiation: Preventing an entity who took part in a
communication from later denying all or part of that communication. As
in, "No, it wasn't me. I didn't buy those 5000 shares of IBM yesterday
before it tanked."