 Cryptography Melissa Pollis

What is Cryptography?  the science or study of the techniques of secret writing, especially code and cipher systems  Important security countermeasure  Used by corporations, businesses, or any organization that wants to secure it’s information  Use of mathematical operations to protect messages traveling between parties or stored on a computer

Roots of Cryptography  2000 BC  Egyptian practice of hieroglyphics  first known use of a modern cipher was by Julius Caesar (100 BC- 44 BC)  Did not trust messengers communicating with governors  “Caesar Cipher” – shifted each letter four places through the alphabet

Roots of Cryptography  Ancient Chinese – used ideographic nature of their language to hide the meaning of certain words  India – government had secret codes to communicate with network of spies throughout their country  Polybius – invented 5 x 5 Polybius square, which is widely used in many cryptographic systems

Polybius Square cipher

Roots of Cryptography  During World War Two, machines were invented that made the ciphers more complicated and difficult to break, and today, computers have made them even stronger still  Evolved from simple ciphers to corporations possibly looking towards new ways to secure their data, because of cracking abilities

Roots of Cryptography  Started as basic transposition ciphers, which assign each letter of the alphabet a particular value  Example is to assign each letter a progressively higher number, where A=1, B=2, and so forth. Using this formula for example, the word "wiseGEEK", once encrypted, would read " ”  Similar to Polybius Square ciphers

Basic Vocabulary  Terminology:  Plaintext:  This refers to the original unencrypted message  The term was coined in the early days when encryption was mostly text-based  Today, plaintext messages can be:  Images,  Sounds,  Videos, or  A combination of several data formats.

Basic Vocabulary  Encryption and Ciphertext:  Encryption is a cryptographic process that turns plaintext into seemingly random streams of bits called ciphertext  The sender sends this ciphertext to the receiver  Eavesdroppers will not be able to make sense of the ciphertext if they do intercept it  However, the receiver will be able to decrypt the ciphertext, turning it back into the original plaintext

Encryption and Decryption  Encryption and decryption require two things  The first is cipher  Cipher:  This is a specific mathematical process used in encryption and decryption.  there are many ciphers, they all operate differently.  Both sides must have the same cipher for the receiver to be able to decrypt the message.  The second requirement is the key

The Key  The Key:  The key is a random string of 40 to 4,000 bits (ones and zeros)  Longer keys are harder to guess and provide stronger confidentiality  For a given cipher, different keys will generate different cipher texts from the same plaintext

Key Length  If there is a key of length N bits, then there are 2 N possible keys  On average, the cryptographer will have to try half of all keys before succeeding  Each additional bit in the key doubles the time it will take to crack it  Some countries have restricted symmetric key lengths in exported products to 40 bits  This is to preserve the ability of govt. agencies to crack the key when they need to

The Simple Cipher  The Simple Cipher:  This cipher works on letters of the alphabet  There are three columns  The first has the text:  Nowisthetime. (Capitals & spaces removed for simplicity)  The second has the key  The key is a series of numbers between 1 and 26  The third column is the ciphertext to be transmitted

Cryptography  The Simple Cipher: PlaintextKeyCiphertext N4R O8W W15L I16… S23… T16… H3… E9… T12… I20… M6… E25…

Cryptography  The simple Cipher:  In this cipher, the plaintext letter is changed to the letter N places later in the alphabet, where N is the number in the key for that letter  So if a plaintext letter is B and the key value is 2, the ciphertext symbol will be D  When you get to the end of the alphabet and have not exhausted N, you continue with A to get the N count  Note: the most common letter in the English alphabet is E. This letter occurs twice in this example but it has different key values each time.  Using a random key each time makes it impossible to analyze the text by letter frequency

Symmetric Key Encryption  Symmetric Key Encryption Ciphers:  Symmetric key encryption uses many specific ciphers that work in the same general way but function very differently in their details  Communication partners must choose a specific symmetric key encryption cipher in order to communicate securely  Only a few common symmetric key encryption ciphers have been well tested, and it is important to select from these few:  RC4, DES, 3DES, and AES

Data Encryption Standard  DES: The Data Encryption Standard.  Created by the National Bureau of Standards in 1977, now called the National Institute of Standards and Technology (NIST)  It quickly became the most widely used symmetric key encryption method  It is still widely used because:  It has survived everything except brute-force exhaustive search attacks  It is widely available, and because  It is supported by hardware accelerators.

Why Use Cryptography?  Original purpose was encryption for confidentiality  Take legible, readable data, and transforming it into unreadable data for the purpose of secure transmission  Use a key to transform it back into readable data once it reaches final destination

Modern Cryptography  Cryptography concerns itself with four main objectives (cryptosystems):  Confidentiality  Integrity  Non-repudiation  Authentication

Modern Cryptography  Confidentiality: information cannot be understood by anyone unintended to see  Integrity: information cannot be altered without detection  Non-repudiation: creator cannot deny at later state his/her intentions  Authentication: sender/receiver can confirm each other’s identity

Government and Cryptography  Battleground of some of the world's best mathematicians and computer scientists  Do not want certain entities in and out of their countries  Do not want other companies to have access to receive and send hidden information  Threat to national interests

Issues of Cryptography  Sender/receiver can fail to keep the key secret  Eavesdropper may learn the key and read the messages  Only works if company enforces organizational processes that do not compromise the technical strengths of cryptography  Poor communication discipline  Example- Japanese Navy in WWII sent messages when there was little need, giving allied cryptologists a large base of messages to examine

References  Pearson Custom Business Resources. N.p.: Pearson Learning Solutions, Print.  "Brief History of Cryptography." Crypto Challenge. Thwate, Inc., Web. 12 Nov  "What is Cryptography?" wiseGeek. Conjecture Corporation, Web. 12 Nov  In-class notes