Cryptography & Encryption: What is it and Why is it used?

Posted by yourlocaltechguy on Feb 21, 2011 in Articles | 0 comments

In this three part series I plan on explor­ing cryp­tog­ra­phy and the his­tory of cryp­tog­ra­phy. 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 stud­ies meth­ods for encod­ing mes­sages so that they can be read only by a per­son who knows the secret infor­ma­tion required for decod­ing, called the key; it includes crypt­analy­sis, the sci­ence of decod­ing encrypted mes­sages with­out pos­sess­ing the proper key, and has sev­eral other branches; see for exam­ple steganography.

Cryp­togra­phies main pur­pose is to hide mes­sages and infor­ma­tion.  One of the ear­li­est forms of cryp­tog­ra­phy was the rear­rang­ing of let­ters in mes­sages. This was known as trans­porta­tion ciphers. A cipher is a sys­tem in which plain text, usu­ally the let­ters, are trans­posed or sub­sti­tuted accord­ing to a pre­de­ter­mined code. Another early form of cryp­tog­ra­phy was the sub­sti­tu­tion of let­ters. One cipher was named after Julius Cae­sar who was said to have used a 3 let­ter shift. This involved sub­sti­tut­ing a let­ter with another let­ter in the alpha­bet three posi­tions away. Cae­sar used this method to com­mu­ni­cate with his gen­er­als in wartimes.

Cryp­tog­ra­phy tries to pro­tect the con­fi­den­tial nature in the com­mu­ni­ca­tions of mil­i­tary lead­ers and diplo­mats. Cryp­tog­ra­phy was used by early Chris­tians to hide some parts of their writ­ings. One exam­ple, 666, the Num­ber of the Beast from the New Tes­ta­ment Book of Rev­e­la­tion, was thought to refer to the Roman Emperor Nero. 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.

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.

Next week I will start to explore the more mod­ern uses of cryp­tog­ra­phy.