Ancient Cryptography

Question 1

ciphers can be thought of as this

Answer 1

virtual locks

Question 2

cryptography requires the understanding of two very old ideas related to

Answer 2

number theory

probability theory

Question 3

first well known cipher used by whom and when

Answer 3

substitution cipher

Julius Ceasar, 58 BC (Caesar cipher)

Question 4

substitution cipher

(Caesar cipher)

Answer 4

shift each letter by so many places

(e.g., advance by 3)

Question 5

The process of lock breaking and code breaking are ____ _____.

Answer 5

very similar

Question 6

when and who, published solution to the Caesar cipher

weakness of the Caesar cipher

Answer 6

published 800 years after Caesar, Arab mathematician (Al-Kindi)

break by knowing frequency in texts of each letter in the alphabet

Question 7

Caesar ciphers are broken by this method

Answer 7

frequency analysis

Question 8

advancement in cryptography in mid-15th century

Answer 8

polyalphabetic cipher

Question 9

polyalphabetic cipher

Answer 9

multiple shifts using code word

(shift text based repeatedly on code word shift indication)

Question 10

polyalphabetic cipher result

Answer 10

flatter distribution of letter frequencies

Question 11

code breakers look for this

Answer 11

information leaks
any differential in letter frequencies is an information leak

Question 12

breaking the polyalphabetic cipher

Answer 12

first determine length of shift word used by checking the frequency distribution of different intervals (four letter code word, frequency distribution of every fourth letter will show the correct distribution)

break five Caesar ciphers in a repeating sequence

Question 13

property of polyalphetetic cipher strength

Answer 13

the longer the code word, the stronger the cipher

Question 14

cipher method from end of 19th century

Answer 14

one-time pad

Question 15

one-time pad encryption method

Answer 15

shift each letter by a random amount given in list of random numbers

both the sender and receiver have this list of random numbers

Question 16

strength of one-time pad

Answer 16

twenty-six to the power of n where n is number of letters in message

Question 17

frequency stability property of randomness

Answer 17

each sequence of length n will be equally likely for a true random sequence

(equally likely to contain every sequence of any length)