Glossary

Iterative:
A system that takes a fairly simple encryption rule and applies it many times to obtain data security.
Plaintext:
The message before going through the encryption, usually abbreviated by the symbol P.
Cipher:
Some method to change a message into a non readable format letter by letter.
Scheme:
A code or cipher, or the description of them.
Encrypt:
To change a message into the unreadable form that can be openly transmitted.
Decrypt:
To change a message from the unreadable form that it was transmitted in to the readable form for human or machine reading. The opposite of encrypt.
Secure:
Effectively unbreakable. A message is considered secure if by the time it can be decrypted by an unintended receiver, the information is useless. Note that for some kinds of information, that means that the message must be effectively impossible to decrypt by an unintended receiver.
One to One:
A mapping is one to one if no more than one element from ever maps to each element of the target set (but not all elements must be hit by the mapping). In other words, a filter is one to one if only one item can ever get mapped to a certain output. Graphically, this would mean a function that is invertible.
Onto:
A mapping is onto if every element of the target set is mapped on at least once (but maybe more than once). In other words, a filter is onto if for every possible output, there is at least one input to the filter that the filter results in that output.
Cryptanalysis:
The art and science of decoding an encrypted message without being the intended receiver, and work which aids that end.
Key:
A short piece of information that is used with the rule for decryption to allow an authorized user to decrypt a message. Often abbreviated as K.
Private Key:
An encryption system that uses a single key for both encryption and decryption, thus the key must be kept private.
Public Key:
An encryption system that uses two keys, so one key is kept private, and the other key can be publically distributed. One key can be used to encrypt, but the other key is required to decrypt.
Round:
Repeating or iterating some function a number of times. So singing Row Row Your Boat over and over again would be singing it in rounds.
DES:

Data Encryption Standard. A standard put forth by the US government around 1977 for sensitive but nonclassified information. Uses a 56 bit key (64 plus 8 parity bits), and 16 rounds. Still considered a reasonably good standard for casual use. Hard to implement in software, easy in hardware. Developed by IBM with technical assisstence from the US government. Was recently (around 1993) renewed for the standard for another 20 years. Some methods now exist that make the most primitive use of this system slightly less secure, and hypothetically breakable given an inordinate amount of time and resources.

As of 2001, DES is considered insecure when attempting to protect against large companies or government organizations. It does still provide adequate security against individuals who do not possess very large amounts of compute power to dedicate to the task.
SKIPJACK:
Algorithm used in the CLIPPER and CAPSTONE chips announced around 1992. It is a classified algorithm that uses a 120 bit long key, though the key is broken up into various parts. The introduction touched off a large controversy due to its classified nature. The algorithm has a known "back door" whereby special keys are "escrowed" or kept by two government agencies to decrypt any message (presumably after obtaining a warrant).
RSA:
Rivest Shamir Adelman. A public key system based on the difficulty of factoring the product of two numbers. Currently patented in the US.
Cryptanalyst:
One who does cryptanalysis.
XOR
A logical function, the exclusive OR. X .xor. Y is true if precisely one of X or Y is true, not both.

Bibliography