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Explor in Computer Sci

by: Marian Kertzmann DVM

Explor in Computer Sci CS 1060

Marketplace > University of Utah > ComputerScienence > CS 1060 > Explor in Computer Sci
Marian Kertzmann DVM
The U
GPA 3.78


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Class Notes
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This 12 page Class Notes was uploaded by Marian Kertzmann DVM on Monday October 26, 2015. The Class Notes belongs to CS 1060 at University of Utah taught by Staff in Fall. Since its upload, it has received 30 views. For similar materials see /class/229983/cs-1060-university-of-utah in ComputerScienence at University of Utah.

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Date Created: 10/26/15
CS 1060 Explorations in Computer Science November 26 2008 LECTURE 3O Cryptography Computer security Information Security The techniques and polices used to ensure proper access to data Examples of data that must be protected and how 0 Any good solution for information security must address Confidentiality ensuring that data is protected from unauthorized access Integrity ensuring that data can only be modi ed by appropriate mechanisms Availability the degree to which authorized users can access information for legitimate purposes CS 1060 Lecture 30 2 Cryptography The eld of study related to encoded information Greek for secret writing enc tion WP plaintext readable decryption ciphertext unreadable A cipher is an algorithm used to perform a particular type of encryptiondecryption Its key is the set of particular parameters that guide the cipher What are some simple ciphers CS 1060 Lecture 30 3 Substitution Ciphers 0 Substitute one character in the plaintext message with another character To decode perform the opposite substitution 0 Example The Caesar cipher shifts the characters of a plaintext message by X positions in the alphabet The key consists of the value of X and the direction to shift P1aintext BRUTUS WILL BETRAY YOU Ciphertext ZPSRSQ UGEE ZCRYW WMS What is the key to the cipher used in this encryption CS 1060 Lecture 30 4 Transposition Ciphers Rearrange the order of existing characters in the plaintext message in a certain way 0 Example The route cipher lays out the message as a grid of characters and speci es a route through the grid The key consists of the dimensions of the grid and the route P1aintext BRUTUS WILL BETRAY YOU Ciphertext BSBYRWEYUITOTLRUULA What is the key to the cipher used in this encryption CS 1060 Lecture 30 Beale Ciphers A set of three ciphertexts describing buried treasure worth over 30 million 1800s This one was deciphered using a book cipher The plaintext reads 1 have deposited in the county of Bedford six feet below the surface of the ground the following articles ten hundred and fourteen pounds of gold CS 10607Lecture 30 Book Cipher 0 Traditionally replace words in the plaintext of a message with the location of words from a book What if a word does not appear in the book 0 Another approach substitutes the rst letter of a word in the book with that words position 0 This Beale ciphertext used a particular edition of the US Declaration of Independence The 115th word in the Declaration of Independence is instituted Use the rst letter of that word quot1quot CS 1060 Lecture 30 7 More on Cryptography Cryptanalysis is the attempt to gure out the plaintext message Without the cipher or its key A challenge for substitution or transposition ciphers How can a computer be used for code breaking 0 Notice that the sender and receiver of an encrypted message must share the cipher key The key must be kept secret otherwise Isn39t the key at as much risk of interception as the messages Should the key be encrypted CS 1060 Lecture 30 8 PublicKey Cryptography Each user has a pair of mathematicallyrelated keys A message encrypted With one Bob k l b d t d 39th ey can on y e ecryp e W1 gt Enc the corresponding partner key Alice39s public key So long as Alice keeps her private key to herself no one else can decrypt the message Alice39s private key CS 10607Lecture 30 9 Computer Security Controlling access to computers involves forcing users to identify themselves using authentication credentials based on something the user knows e g password based on something the user has e g smart card based on biometrics e g ngerprint 0 Unfortunately keeping unauthorized users out of a computer system is not enough In what other ways might security be compromised CS 1060 Lecture 30 10 Malicious Code VzruS a malicious program that embeds a copy of itself in another program Typically does damage by corrupting or deleting files on a particular computer Worm a standalone selfreplicating malicious program Typically does damage on networks by consuming bandwidth T rojan horse a program that appears to be helpful but actually causes some kind of problem when executed Standalone but does damage to computer on which it executes CS 1060 Lecture 30 11 Security Attacks Password guessing Unlike a human a computer is happy to use brute force Such programs will often try every word in an online dictionary 0 Phishing uses an officiallooking web page to collect information such as usernames and passwords The development of software can leave systems vulnerable to attack whether intentional e g back door or unintentional eg buffer over ow CS 1060 Lecture 30 12


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