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computer science

CSCI 1001. overview of. computer science. COMPUTER SECURITY II. cryptography. CAESAR’S CIPHER. To write a secret message, . 1) Write down each plaintext letter. ATTACK AT DAWN. 2) Count ahead three letters from each plaintext letter to get a ciphertext letter. A B C D. T

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computer science

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  1. CSCI 1001 overview of computer science COMPUTER SECURITY II

  2. cryptography

  3. CAESAR’S CIPHER To write a secret message, 1) Write down each plaintext letter ATTACK AT DAWN 2) Count ahead three letters from each plaintext letter to get aciphertextletter. A B C D T U V W T U V W A B C D C D E F K L M N A B C D T U V W D E F G A B C D W X Y Z N O P Q

  4. BREAKING CAESAR’S CIPHER THOR RIP ARM OFF UNLESS YOU TELL SECRET! I’LL ROTATE LETTERS A DIFFERENT AMOUNT FOR EACH GENERAL. THE AMOUNT IS LIKE A KEY TO “UNLOCK” MY MESSAGES

  5. A A A A B B B B C C C C D D D D E E E E F F F F G G G G H H H H I I I I J J J J K K K K L L L L M M M M N N N N O O O O P P P P Q Q Q Q R R R R S S S S T T T T U U U U V V V V W W W W X X X X Y Y Y Y Z Z Z Z A A A A B B B B C C C C D D D D E E E E F F F F G G G G H H H H I I I I J J J J K K K K L L L L M M M M N N N N O O O O P P P P Q Q Q Q R R R R S S S S T T T T U U U U V V V V W W W W X X X X Y Y Y Y Z Z Z Z ROTATION CIPHERS CAESAR ROTATES BY 3 ROTATE BY 11 FOR GENERAL 1 ROTATE BY 17 FOR GENERAL 2 SPECIAL CASE: ROT13

  6. BREAKING ROTATION HOW MANY POSSIBLE KEYS? FYNNW UCBLCQBYW

  7. SUBSTITUTION A B C D E F G H I J K L M N O P Q R S T U V W X Y Z G O P H E R S K I U M A Z Y X W V T Q N L J F D C B RUNNING BACKS → TLYY IYSO GPMQ NXLP KHXF YQDD → TOUCHDOWNS XX IYNP RQNG HILZ → IN TCF STADIUM How many possible keys? 26 × 25 × 24 × … = 4.03 × 1026

  8. BREAKING SUBSTITUTION FREQUENCY ANALYSIS: GUESS MOST COMMONLETTER = E, T, A, O, I, N, S, H, R…

  9. EXAMPLE E T T11 O10 W8 G7 V 6 Q5 J5 D4 R 3 A3 T E E E T T E T E T E T T E T E E E T E ETAOINSHRDLUCMWFG…

  10. EXAMPLE T11 O10 W8 G7 V 6 Q5 J5 D4 R 3 A3 H E T O H I I I T T T T T T T T T T E E E E E H H H H A A H H H H T T T T T H H H I I I A A H O E E E E E E E E E E D H H H V H H H H E E E E E A A T T T T T O E E E E E S P X E E E E E A C H H H H I I I E E E E E E E E E T T T T T H H H H E E E E E H H H H E W O A A H O F A A T H H H BU T T T T T T T T T M O H H H H E E E E E I I I H H H H A A T T T T T I N N S S R W ETAOINSHRDLUCMWFG… N S R W S SS W R N W R S W

  11. FE YDC DMCGAB TCG'Y HPSK P MFAVY, YMI YVMKK ETAOINSHRDLUCMWFG…

  12. gxmod P gymod P (gx)y mod P (gy)x mod P gx is Google’s Public Key x is Google’s Private Key

  13. CERTIFICATES gxmod P or ? Private Keys can be used to make unforgeabledigital signatures on data A certificate is a digitally signed name + Public Key.

  14. http://cs1001.us/ Please look at practice midterm

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