Codebusters Test Codebusters Pattern Recognition 2 — Questions and Answers
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?
- E (Correct answer)
- Z
- X
- Q
Correct answer: E
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?
- TELL (Correct answer)
- WORD
- SHIP
- FAST
Correct answer: TELL
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?
- HELLO (Correct answer)
- WORLD
- CODES
- GAMES
Correct answer: HELLO
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?
- TH (Correct answer)
- QU
- ZX
- BV
Correct answer: TH
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?
- A or I (Correct answer)
- E or T
- S or N
- O or R
Correct answer: A or I
The only common single-letter English words are 'A' and 'I', making these the top candidates for a lone ciphertext letter.
Question 6: In a Patristocrat cipher, spaces between words are removed. Which technique is most useful for finding word boundaries?
- Identifying frequently repeated 2-3 letter sequences (Correct answer)
- Trying all 25 Caesar shifts
- Converting letters to numbers
- Matching Morse code dot-dash patterns
Correct answer: Identifying frequently repeated 2-3 letter sequences
Without spaces, high-frequency short sequences (like 'THE' and 'AND') act as anchors for locating word breaks in a Patristocrat.
Question 7: A ciphertext ends with the 4-letter pattern 'JKKJ'. Which common English word has the same ABBA structure?
- NOON (Correct answer)
- ABLE
- TION
- NESS
Correct answer: NOON
JKKJ follows pattern ABBA where outer letters match and inner letters match; NOON (N-O-O-N) has exactly this structure.
Codebusters Test Codebusters Pattern Recognition 2
In an Aristocrat cipher, the ciphertext letter 'Q' appears far more frequently than any other letter.
What is the most likely plaintext equivalent?