Computer Science

1. Computer Science Mrs. Myers

2. Computer Science • Introduction • Binary Counting • Encryption and Decryption

3. Cryptography • The objection: • Explain the principles of encryption • Use different methods to construct simple ciphers • Understand the principle behind breaking codes

4. Computer Science • http://www.youtube.com/watch?v=dU1xS07N-FA • Coding video

5. Coding • Richland School District Offers Three Computer Science Courses • Alice • Introduction to Java I • Intermediate Java II

6. Computer Science Alice: developed by Randy Pausch at • Freshman to Senior • Graphics Introduction to Coding • Half of Year

7. Computer Science Introduction To Java I • CS0007: 3 Credit Course through University of Pittsburgh • Service Course at universities, expected to be done if majoring in Computer Science, many students transfer it for computer skills requirement • Learn basic skills to create and accomplish small basic tasks. • Must be successful in Geometry • Sophomore - Senior

8. Computer Science Intermediate Java II • CS401: 4 Credit Course through University of Pittsburgh • First CS Course if majoring in Computer Science • Must be successful in Java I • Junior - Senior

9. Computer Science • Through out the recession TWO industries have grown and are hiring new employees: • Medical • Computer Science

10. Binary Counting Computers operate entirely with 1’s & 0’s

11. Binary Counting Either the switch is on or off.

12. Binary Counting • ENIAC was invented by J. Presper Eckert and John Mauchly at the University of Pennsylvania and began construction in 1943 and was not completed until 1946. • It occupied about 1,800 square feet and used about 18,000 vacuum tubes, weighing almost 50 tons.

13. Oh by the way . . . • Oxford University Graduate, • Tim Berners-Lee invented the World Wide Web, while at CERN, the European Particle Physics Laboratory, in 1989.

14. Oh by the way . . . • Machine Language is binary, the base of how computers operate. • We program in higher order languages, such as Java to create programs. These languages use words such as if, else, while, and, for.

15. Oh by the way . . . • Then our code is compiled to assembly language (hexadecimal is base 16). It uses the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen.

16. Oh by the way . . . • Then hex translates to binary or machine language for the computer to execute every command.

17. Oh by the way . . . • When you are a programmer you are the master of your own universe.

18. Binary Counting • Binary is Base 2 (2 chooses for digits 0 & 1) • We normally use the Decimal System, Base 10 0, 1, 2, 3, 4, 5, 6, 7, 8, 9: 10 Chooses for digits Why?

19. Binary Counting • Binary is base 2 (2 chooses for digits 0 & 1) • We use base 10

20. Back to Binary Counting • Binary is base 2 (2 chooses for digits 0 & 1)

21. Back to Binary Counting • Binary is base 2 (2 chooses for digits 0 & 1)

22. Back to Binary Counting • Binary is base 2 (2 chooses for digits 0 & 1)

23. Back to Binary Counting • Bigger than 15????

24. Back to Binary Counting • Practice converting numbers from base 10 (decimal) to base 2 (binary) • Worksheet

25. Cryptography • Activities the internet is used for? • How is information protected?

26. Cryptography • The basis of data protection is called: • Encryption: converting info from an easily understood form into a code that cannot be read or broken. • We will learn about 2 coding technologies based on encryption.

27. Cryptography • 1. A Greek scytale • 2. Substitution Code or shift Cipher

28. Cryptography • http://www.youtube.com/watch?v=k7e-rrhV7rA • How to make a scytale: • Scytale • WS

29. Cryptography • Disadvantages to scytale: • Examples of situations that need secrecy: • Military operations need secrecy.

30. Cryptography • During World War II, the Enigma machine enabled Germans to attack Allies. • However, when the machine was captured on a German U-boat, the Allies were able to decode intercepted German messages.

31. Cryptography • The intercepted German messages enabled the Allies to find and destroy the German U-boats, turning the tide of the war.

32. Cryptography • Another way to encode info is to systematically substitute one letter for a different one. This is how the Engima machine works. • Engima Machine • BUT Substitution code originated long before WWII.

33. Cryptography • It sometimes called Caesar’s cipher.

34. Cryptography • WS to make a Caesar Wheel: • Remember: • Encoded message = BLACK to RED • Decoded message = Red to Black • WS using wheel.

35. Cryptography • Modular arithmetic has been used for years as a means of encoding messages. • Modular math means look at remainder. • 8÷3 Quotient: • 8÷3 Remainder: • or 8 MOD 3 =

36. Cryptography Original Letter to Number Equivalencies: and then the numbers are changed via an affine (linear) transformation to new, coded numbers. The coding function has the form: • Y = A * X + B (MOD 26)

37. Cryptography • Y = (A * X + B) (MOD 26) • X is the uncoded number, • A is the multiplier, B is the constant (both A and B known to allies, but unknown to enemies) and Y is the calculated, coded number. • The arithmetic is done mod 26 to ensure that we get numbers back that can be translated back to letters before sending the coded message. • WS

38. Cryptography • This method of coding messages is ancient. In fact, Caesar is said to use the cipher with A = 1 and B = 3. This method of coding is fun to play with, but easy to crack. • Modern coding techniques still make use of modular arithmetic, but in a highly sophisticated way.

39. Cryptography • You were given the shift. • How do code breakers break codes. • One way is to look at frequency of letter use in language. They look at most frequently used letter (Anyone Know???) and work from there.

40. Cryptography • We’ve talked about several “ancient” ways to encode and decode messages. • Does anyone know how computers secure data.

41. Cryptography • public key • The key pair is based on prime numbers (numbers that only have divisors of itself and one, such as 2, 3, 5, 7, 11 and so on) of long length. This makes the system extremely secure, because there is essentially an infinite number of prime numbers available, meaning there are nearly infinite possibilities for keys.

42. Cryptography • To implement public-key encryption on a large scale, such as a secure Web server need more. • A digital certificate is basically a unique piece of code or a large number that says that the Web server is trusted by an independent source known as a certificate authority. • The certificate authority acts as a middleman that both computers trust. It confirms that each computer is in fact who it says it is, and then provides the public keys of each computer to the other.

43. Cryptography • The padlock symbol lets you know that you are using encryption.

44. Cryptography • Public keys generally use complex algorithms and very large values for encrypting, including 40-bit or even 128-bit numbers. • A 128-bit number has a possible 2128, or 3,402,823,669,209,384,634,633,746,074,300,000,000,000,000,000,000,000,000,000,000,000,000 different combinations -- this would be like trying to find one particular grain of sand in the Sahara Desert.

45. Cryptography • A 128-bit number has a possible 2128, or 3,402,823,669,209,384,634,633,746,074,300,000,000,000,000,000,000,000,000,000,000,000,000 • By the way a number followed by 57 digits is • Called an Octadecillion. • Conclusion ws

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