Ancient Cryptography Flashcards Preview

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Flashcards in Ancient Cryptography Deck (17)
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1
Q

ciphers can be thought of as this

A

virtual locks

2
Q

cryptography requires the understanding of two very old ideas related to

A

number theory

probability theory

3
Q

first well known cipher used by whom and when

A

substitution cipher

Julius Ceasar, 58 BC (Caesar cipher)

4
Q

substitution cipher

(Caesar cipher)

A

shift each letter by so many places

(e.g., advance by 3)

5
Q

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

A

very similar

6
Q

when and who, published solution to the Caesar cipher

weakness of the Caesar cipher

A

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

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

7
Q

Caesar ciphers are broken by this method

A

frequency analysis

8
Q

advancement in cryptography in mid-15th century

A

polyalphabetic cipher

9
Q

polyalphabetic cipher

A

multiple shifts using code word

(shift text based repeatedly on code word shift indication)

10
Q

polyalphabetic cipher result

A

flatter distribution of letter frequencies

11
Q

code breakers look for this

A

information leaks
any differential in letter frequencies is an information leak

12
Q

breaking the polyalphabetic cipher

A

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

13
Q

property of polyalphetetic cipher strength

A

the longer the code word, the stronger the cipher

14
Q

cipher method from end of 19th century

A

one-time pad

15
Q

one-time pad encryption method

A

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

both the sender and receiver have this list of random numbers

16
Q

strength of one-time pad

A

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

17
Q

frequency stability property of randomness

A

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

(equally likely to contain every sequence of any length)