Codebusters Test Codebusters Pattern Recognition 2

Question 1

In an Aristocrat cipher, the ciphertext letter 'Q' appears far more frequently than any other letter. What is the most likely plaintext equivalent?

Accepted Answer

E

Answer

In English, 'E' is the most frequent letter (~13%), so the most common ciphertext letter typically maps to 'E'.

Question 2

A ciphertext word reads 'VHOO'. What common English word does the ABCC double-letter pattern suggest?

Accepted Answer

TELL

Answer

VHOO follows pattern ABCC (two unique letters then a doubled letter), matching TELL (T-E-L-L).

Question 3

In a Caesar cipher with a shift of 13 (ROT13), what does the ciphertext 'URYYB' decode to?

Accepted Answer

HELLO

Answer

ROT13 shifts each letter back 13 positions: U→H, R→E, Y→L, Y→L, B→O, spelling HELLO.

Question 4

Which digraph (two-letter combination) appears most frequently in standard English text?

Accepted Answer

TH

Answer

TH is the most common English digraph, appearing in high-frequency words like 'the', 'that', 'this', and 'there'.

Question 5

A ciphertext contains the single-letter word 'X'. What are the two most likely plaintext letters it represents?

Accepted Answer

A or I

Answer

The only common single-letter English words are 'A' and 'I', making these the top candidates for a lone ciphertext letter.

Codebusters Test Practice Test