Welcome to Wikiversity's content develop area for all things related to information security.
Hardware Disconnect or Isolation 
Many methods of information security have been devised for communications, data transfer, data processing, etc. In general, it has been found that what one set of computers can encrypt or process another can decrypt and process. The best security devised to date is physical isolation of information, media and hardware. Unfortunately this is very expensive and in some cases impossible, particularly in communications.
Terms: Plaintext - Information presented in it's natural/unencrypted form
Ciphertext - Information that has been obfuscated through some means of cryptography
Entropy - The introduction of some additional randomness to the cryptographic function
Salt - A unique value which is married to the plaintext before encryption
Encryption is a process where plaintext is transformed using some algorithm and sometimes additional information to effectively protect the information from unauthorized individuals.
Salts are often used in conjunction with one-way hashing algorithms such as those used in common password schemes. Salts are values which are unique to the record, but static to the file. By adding this record level uniqueness, brute force and dictionary attacks are less likely to be successful (or at least much more time consuming).
One-way hashing algorithms are functions that are designed to prevent reversing the operation to render the original information. This is mainly useful for integrity and authentication. These algorithms are often based on the use of incredibly large prime numbers.