CRYPTOGRAPHY

INTRODUCTION

CRYPTOGRAPHY IS A SUBJECT THAT HAS BEEN STUDIED AND APPLIED SINCE ANCIENT ROMAN TIMES, AND RESEARCH INTO BETTER ENCRYPTION METHODS CONTINUES TO THIS DAY.

CRYPTOGRAPHY IS THE ART OF ENCODING AND DECODING MESSAGES SO THAT MESSAGES CAN BE SECURELY TRANSMITTED FROM A SENDER TO A RECEIVER WITHOUT FEAR OF AN OUTSIDE PARTY INTERCEPTING AND READING OR ALTERING THE MESSAGE'S CONTENTS.

INTRODUCTION CONTDWHO USES CRYPTOGRAPHY?

GOVERNMENTS

SPIES

BANKS

CREDIT CARD COMPANIES

HISTORY

CAESAR'S ALPHABET

THE MOST WIDELY-KNOWN FORM OF CRYPTOGRAPHY IS CAESAR'S ALPHABET. IT'S A VERY SIMPLE SUBSTITUTION CIPHER - A LETTER SHIFT. EVERY LETTER IN THE ALPHABET IS SHIFTED A CERTAIN NUMBER OF LETTERS TO THE LEFT. THE MOST COMMON KEY IS THREE. HERE IS THE ALPHABET AS WE KNOW IT, FOLLOWED BY CAESAR'S 'ENCRYPTED' ALPHABET:

ABCDEFGHIJKLMNOPQRSTUVWXYZ DEFGHIJKLMNOPQRSTUVWXYZABC

PRETTY SIMPLE, NO? AS SUCH, THE 'CLEARTEXT' OF 'THIS IS AN ENCRYPTED MESSAGE' WOULD BECOME THE 'CIPHERTEXT' OF 'WKLV LV DQ HQFUBSWHG PHVVDJH'.

HISTORY OF CRYPTOGRAPHY ENIGMA

DEVELOPED IN WORLD WAR II BY THE GERMAN NAVY IN ORDER TO PASS SECRET MESSAGES WITHOUT THE PESKY ALLIES GETTING THE MESSAGES AND INTERFERING WITH THE PLANS.

THE SYSTEM WAS PRIMARILY MECHANICAL AND WAS A STREAM CIPHER - EVERY POINT IN THE MESSAGE AFFECTED EVERY LATER POINT.

ENIGMA USED A SERIES OF ELECTRICALLY-CONNECTIVE WHEELS TO EXCHANGE ONE LETTER INTO ANOTHER MULTIPLE TIMES.

MOST ENIGMA MACHINES HAD SPACES FOR THREE WHEELS, ALTHOUGH LATER INCARNATIONS USED FOUR WHEELS TO CONFOUND THE ALLIED CRYPTANALYSTS.

THESE WHEELS WERE CHOSEN OUT OF ONLY A FEW POSSIBLE WHEELS. THE STANDARD ENIGMA MACHINE CAME WITH FIVE POSSIBLE WHEELS.

THE GERMAN ARMY AND AIR FORCE USED A STANDARD WHEEL SET, WHILE THE NAVY USED A SET OF EIGHT WHEELS.

ENIGMA ITSELF WAS A RECIPROCAL CRYPTOGRAPHY SYSTEM - PROVIDED THAT THE MACHINE HAD BEEN RESET, ALL ONE NEEDED TO DO TO DECRYPT A MESSAGE WAS TO ENTER THE CIPHERTEXT INTO THE KEYBOARD, AND THE CLEARTEXT WOULD BE OUTPUT ON THE DISPLAY.

HISTORY OF CRYPTOGRAPHY

THE DATA ENCRYPTION STANDARD (DES)

THE HISTORY OF DES IS LONG AND CONVOLUTED, BUT IN SHORT IT SUCCESSFULLY BROUGHT CRYPTOGRAPHY OUT OF STRICTLY GOVERNMENTAL USE AND INTO THE COMMERCIAL MARKET.

ORIGINALLY KNOWN AS LUCIFER AND DEVELOPED AT IBM, DES WAS IBM'S ATTEMPT TO FORM A VIRTUAL MONOPOLY IN THE DIGITAL WORLD.

DES INTRODUCED CRYPTOGRAPHY TO THE CONSUMER.

MODERN TECHNIQUES IN CRYPTOGRAPHY

SUBSTITUTION CIPHERS

SUBSTITUTION CIPHERS ARE THE MOST SIMPLE, BECAUSE THEY SWITCH ONE LETTER FOR ANOTHER, THROUGHOUT THE LENGTH OF A MESSAGE.

THEY ARE EASILY BROKEN BY ANALYSING THE FREQUENCY OF LETTERS IN THE CIPHERTEXT AND APPLYING THE MOST COMMONLY-USED LETTERS IN THE APPROPRIATE PLACES.

RECIPROCAL CIPHERS

RECIPROCAL CIPHERS ENCOMPASS MORE CRYPTOGRAPHY SYSTEMS, AND CAN MAKE A SYSTEM EITHER LESS SECURE OR MORE USABLE.

A RECIPROCAL CIPHER MEANS, JUST AS ONE ENTERS THE CLEARTEXT INTO THE CRYPTOGRAPHY SYSTEM TO GET THE CIPHERTEXT, ONE COULD ENTER THE CIPHERTEXT INTO THE SAME PLACE IN THE SYSTEM TO GET THE CLEARTEXT.

USING A RECIPROCAL SUBSTITUTION IS A FORM OF CRYPTOGRAPHIC SUICIDE - IT MAKES THE CIPHER HALF AS DIFFICULT TO BREAK.

HOWEVER, IF ENIGMA WEREN'T RECIPROCAL, IT WOULD HAVE BEEN SIGNIFICANTLY MORE DIFFICULT TO IMPLEMENT.

SYMMETRIC CIPHERS

FOR A LONG TIME, SYMMETRIC CIPHERS WERE THE ONLY FORM OF CRYPTOGRAPHY AVAILABLE.

A SYMMETRIC CIPHER USES THE SAME KEY FOR ENCRYPTION AND DECRYPTION.

GENERALLY, SYMMETRIC CIPHERS ARE MORE SECURE THAN ASYMMETRIC CIPHERS, SINCE, IN MOST MODERN CRYPTOGRAPHY SYSTEMS, SECURING THE KEY IS MORE IMPORTANT THAN SECURING THE CRYPTOGRAPHY SYSTEM ITSELF.

STREAM AND BLOCK CIPHERS

ASYMMETRIC CIPHERS THE IDEA OF ASYMMETRIC (OR PUBLIC KEY) CRYPTOGRAPHY WAS FIRST PUBLISHED IN 1976 BY WHITFIELD

DIFFIE AND MARTIN HELLMAN IN THEIR PAPER "NEW DIRECTIONS IN CRYPTOGRAPHY" (MENEZIE, 2).

AN ASYMMETRIC CIPHER IS ANOTHER NAME FOR A 'SPLIT-KEY' ALGORITHM.

VERY FEW SPLIT-KEY ALGORITHMS EXIST IN THE WORLD OF CRYPTOGRAPHY.

THE CONCEPT OF SPLIT-KEY CRYPTOGRAPHY EMERGED IN 1975.

IT REVOLUTIONISED CRYPTOGRAPHY, AS NOT ONLY COULD THE RECIPIENT OF A MESSAGE KNOW THAT ONLY HE COULD READ THE CONTENTS, BUT THAT THE MESSAGE ALSO COULD HAVE COME ONLY FROM THE SENDER.

THEY USE PUBLIC KEY AND PRIVATE KEY

EACH KEY, HOWEVER HAS A DUAL PURPOSE.

SO FAR NEITHER OF THE PUBLIC KEY ALGORITHMS HAVE BEEN PROVEN SECURE.

THE LEVEL OF SECURITY IS DEPENDENT ON HOW MUCH COMPUTING POWER THE CRYPTANALYST HAS, HOW MUCH TIME HE TAKES TO BREAK THE CIPHER TEXT, AND THE LENGTH OF THE KEY USED.

QUANTUM CRYPTOGRAPHY TO UNDERSTAND THESE CHANGES AND WHY THEY MUST TAKE PLACE, ONE MUST FIRST LOOK AT THE

PHYSICS PRINCIPLES BEHIND BOTH QUANTUM COMPUTING AND QUANTUM CRYPTOGRAPHY.

THREE QUANTUM MECHANICAL PHENOMENA THAT ARE USED UNIQUELY IN BOTH OF THESE ARE THE UNCERTAINTY PRINCIPLE, SUPERPOSITION, AND ENTANGLEMENT.----

QUANTUM COMPUTING CAN UTILIZE THIS PROPERTY TO CARRY OUT CERTAIN COMPLEX COMPUTATIONS VERY QUICKLY.

ENTANGLEMENT IS THE QUANTUM MECHANICAL PHENOMENA IN WHICH THE QUANTUM STATES OF TWO OR MORE PARTICLES ARE LINKED, EVEN WHEN THEY BECOME SPATIALLY SEPARATED.

FOR EXAMPLE, AFTER TWO PARTICLES ARE CREATED THAT ARE ENTANGLED, BOTH PARTICLES WOULD HAVE A PROBABILITY OF HAVING A CERTAIN SPIN.

WHEN THE MEASUREMENT IS MADE ON THE FIRST PARTICLE, THEREBY FORCING IT INTO A SINGLE STATE, ITS ENTANGLED PARTICLE THEN ALWAYS WILL BE MEASURED TO HAVE THE OPPOSITE SPIN.