1. One of the major areas of infosec, integrity is the area concerned with making sure that messages/information are "correct" and haven't been subtly changed or tampered with by an adversary. Analogy: We write the dollar amount on personal checks both as numbers as well as words. This prevents somebody from altering the value, such as adding an extra digit to the number in order to extract $1000 from you rather than the authorized $100. Key point: We use cryptographic hashes as a way of fingerprinting documents and detecting when they are changed. The two most popular hashes are SHA-1 and MD5. Key point: Typical attacks against integrity include modification, insertion, deletion, and replay of information. Contrast: The terms integrity and authenticity are widely used to mean the same thing. In other situations, they have subtly different meanings (especially law). The term integrity generally describes defenses against malicious alteration of a message once it has been sent, whereas authenticity also implies some validation of the sender of the message to protect against forgeries. Contrast: Another way looking at integrity is system integrity. The concern is maintaining the integrity of the computer itself, rather than a message that goes across the wire. In this context, the goals are to prevent files from being modified or programs from being installed on the system. One of the focuses of system integrity is making sure that legitimate, authorized users do not make unauthorized modifications to the system. Programs like tripwire check the integrity of systems by maintaining a table of hashes for all files, and detecting which files change. See also: Integrity is often mentioned along with other key security concepts such as confidentiality, authentication, and non-repudiation. From Hacking-Lexicon