Codebusters Test Codebusters Pattern Recognition 4

Question 1

What does the index of coincidence primarily help determine in cipher analysis?

Accepted Answer

Whether a cipher is monoalphabetic or polyalphabetic

Answer

The exact Caesar shift value

Answer

The number of letters in a keyword

Answer

Whether the message is in English or Spanish

Question 2

Using A=1, B=2...Z=26, what does the number sequence '8-5-12-12-15' decode to?

Accepted Answer

HELLO

Answer

WORLD

Answer

CODES

Answer

BINGO

Question 3

A ciphertext has nearly flat letter frequency (all 26 letters appear almost equally often). This most strongly suggests which cipher type?

Accepted Answer

Vigenère or polyalphabetic substitution

Answer

Simple Caesar shift

Answer

Monoalphabetic substitution

Answer

Rail fence transposition

Question 4

In a Baconian cipher, each letter is encoded as a 5-character sequence of A's and B's. How many unique letters can this system encode?

Accepted Answer

32

Answer

26

Answer

25

Answer

52

Question 5

A ciphertext word has pattern 'ABBA' (e.g., 'NOON'). Which 4-letter English word also fits this pattern?

Accepted Answer

DEED

Answer

THAT

Answer

CODE

Answer

SHIP

Question 6

In a 2-rail fence cipher applied to 'SCIENCE', which letters land on the top rail?

Accepted Answer

S, I, N, E (positions 1,3,5,7)

Answer

C, E, C (positions 2,4,6)

Answer

All vowels

Answer

The first half of the word

Question 7

Which doubled-letter combination appears most frequently in standard English text?

Accepted Answer

LL

Answer

QQ

Answer

XX

Answer

ZZ