The U.S. National Information Systems Security Glossary defines Information systems security (INFOSEC) as:
Most definitions of information security tend to focus, sometimes exclusively, on specific usages and, or, particular media; e.g., "protect electronic data from unauthorized use". In fact it's a common misconception, or misunderstanding, that information security is synonymous with computer security - in any of its guises: computer and network security, information technology (IT) security, information systems security, information and communications technology (ICT) security. Each of these has a different emphasis, but the common concern is the security of information in some form (elelctronic in these cases): hence, all are subsets of information security. Conversely, information security covers not just information but all infrastructures that facilitate its use - processes, systems, services, technology, etc., including computers, voice and data networks, etc.
It is an important point that information security is, inherently and necessarily, neither hermetic nor watertight nor perfectible. No-one can ever eradicate all risk of improper or capricious use of any information. The level of information security sought in any particular situation should be commensurate with the value of the information and the loss, financial or otherwise, that might acrue from improper use - disclosure, degradation, denial, or whatever. Bruce Schneier makes this point in Secrets and Lies: information security is about risk management.
Three widely accepted elements (aims, principles, qualities, characteristics, ... ) of information security are:
These can be remembered by the mnemonic “CIA”.
A further, generally accepted element is:
Historically, up to about 1990, confidentiality was the most important element of information security, followed by integrity, and then availability. By 2010, changing use and expectation patterns had moved availability to the top of most versions of this priority list. The first goal of modern information security has, in effect, become to ensure that systems are predictably dependable in the face of all sorts of malice, and particularly in the face of denial of service attacks.
Some other facets of information security are:
Cryptography and Cryptanalysis are important tools in assuring confidentiality (in tranmission or storage of information), integrity (no change can be made undetectably), and source identification (the sender can be identified and all other than that sender can be excluded). Always assuming, necessarily, that the key(s) involved have not been misued or compromised, and that the crypto systems employed have been well chosen and properly used.