what is cryptology?

Question

how to use one or two keysin transformation?

Answer 1

It is the study and breaking of codes. Transform away..

Answer 2

Cryptography is the science of concealing a message's meaning rather than its existence. It can be subdivided into codes and ciphers. Codes are based on linguistic entities of variable character length such as syllables, words and phrases. Ciphers are based on fixed length elements without regard to meaning.

The original message is known as plaintext and can be either encoded to codetext or enciphered to ciphertext. To read the message afterwards it must be either decoded or deciphered.

Codes normally involve code books which are lists of words or phrases and their replacement codes. If the replacement codes are in the same alphabetic order so that the same list can be used for decoding, it is known as a one-part code. If a second list is needed to sort the codes alphabetically, then the encoding scheme is known as a two-part code. The difficulty of codes is that the code itself must be distributed to all readers and if the code book gets into insecure hands, the code is compromised and a new code needs to be distributed.

Ciphers on the other hand rely on a system algorithm or procedure for encoding without need for a code book. Sometimes this system also requires a keyword for correct use. This allows a cipher to continue in use even when its system is known by others and even when a single keyword is known. Changing the keyword in current use once again conceals the meaning.

An interesting sidenote to codes and ciphers is that the 'native' language of the plaintext may cause problems for decrypting (reading by cracking the unknown algorithm). Sometimes it is just a localism or obscure way of saying something. Or the plaintext can be anagrams easily read by a 'native' but difficult for others such as:

Aoccdrnig to a rscheearch at an Elingsh uinervtisy, it deosn't mttaer
in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is
taht frist and lsat ltteer is at the rghit pclae. The rset can be a
toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae
we do not raed ervey lteter by itslef but the wrod as a wlohe.
Another example is the use of an obscure foreign language to delay decryption until the message's purpose has been served. The Navaho code talkers of WW2 fame is a perfect illustration. Look at the code used at Code Talk.

Since the most interesting aspects of cryptology (at least for me) are the methods of enciphering and those of 'cracking' the messages, this site will emphasize cipher techniques rather than coding ones.