Cryptography is such a broad part of our lives we do not even notice the smallest applications, shopping on eBay or watching satellite television. I bet you even used cryptology when you were in school and did not even know it. Ever write a message in numbers instead of letters? Each letter of the alphabet correlated to its number position in the alphabet. The number sequence 3,16,25,12,20,15,12,15,7,25 equals cryptology. This is a form of cryptology in its most basic form. Webster's dictionary defines Cryptography as :
n. 1. The act or art of writing in code or secret characters; also, secret characters, codes or ciphers, or messages written in a secret code.
2. The science which ...view middle of the document...
One of Nero's policies was the persecution of Christians. Lovers are instructed to use cryptography to communicate without being discovered in the Kama Sutra. 
Information in original form is called plaintext, the encrypted form is called ciphertext. Texts encrypted by classical ciphers reveal numeric information about the message, which can be used to break the cipher. A classical cipher is a cipher that uses an alphabet of letters and usually is implemented by hand or simple machine. Classical ciphers are no longer used due their simple nature. With the discovery of frequency analysis (around the 10th century), by the Arabs, just about all ciphers of this kind became vulnerable by a fellow cryptographer. Frequency Analysis is based on the commonality of letters in a given language such as st' and th' in the English language. An example would be the letter e is used quite often versus the letter x is rarely used.
A basic understanding of the statistics of the plaintext language and some problem solving skills including patience when done by hand are all that is required. These types of ciphers are still used today mostly in puzzles. Practically all ciphers remained vulnerable to this type of attack until Leon Battista Alberti invented the polyalphabetic cipher around the year 1467. His innovation used different ciphers for varying parts of a message. He invented the first automatic cipher device, a wheel which switch alphabets after several words. The polyalphabetic Vigenère cipher uses a key word in controlling letter substitution based on which letter of the key word is used.  Though an improvement, ciphers were still partially vulnerable to frequency analysis techniques. This was discovered in the mid 1800s by Charles Babbage.
Modern uses of cryptology date back to World War I. The US was helping the British capture and decipher messages from Germany. At this point in the war the US had remained neutral. Then a telegram was intercepted (The Zimmermann telegram) from Germany to Mexico. Basically what it said was that Germany would divide up the US with Mexico if they would help in the war effort. The US ended its position of neutrality soon after. 
In World War II, there were many uses of cryptology. The infamous Enigma machine used by the German military was one of the more famous ones. This was an electro-mechanical, portable cipher machine. It was able to encrypt and decrypt messages. The Enigma machine was a combination of keys, plugs and rotors creating a complex mechanical machine. The Enigma was first commercial available in the 1920's. Governments and military of many nations adopted this type of cryptography. A British mathematician, Alan Turing, was able to crack the code which helped in the Allied victory. The US was also successful in breaking many of the Japanese codes too. This lead to a win at Midway Island, turning the war in the Pacific. Another message that was intercepted lead to the death of...