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Codebusters - Random Aristocrat

Last reviewed October 12, 2026

Practice this event
On this page(11 sections)
Type: Inquiry
Divisions: B, C
Participants: Up to 3
Approx. Time: 50 minutes
Allowed Resources: Writing utensils only: no notes and no calculator. The supervisor hands out a resource sheet (the Div B sheet adds an Atbash table).

A random Aristocrat is a monoalphabetic substitution built on a random alphabet. Every plaintext letter is replaced by one fixed cipher letter everywhere it appears, the word spaces stay where they are, and the substitution table is a shuffled 26-letter alphabet with no keyword behind it. The surviving spaces reveal word lengths, which is what makes it solvable by hand. The timed first question on a Codebusters exam is an Aristocrat, and a random alphabet is one of the Aristocrat types the rules allow for it, so your speed on this cipher feeds directly into the timing bonus.

What the rules cover

Under the 2027 rules, random-alphabet Aristocrats are on the Regional list in both divisions (rule 3.e.i), and State and National tests may use every Regional code type (3.f.i), so the cipher can appear at all three levels. The table summarizes the 2027 rules manual, with section numbers.

ItemDivision BDivision C
LevelsRegional, State and National (3.e.i, 3.f.i)Same
Alphabets allowed for AristocratsK1 or random (ACA definitions), with or without a hint (3.e.i)K1, K2, K3 or random (ACA definitions), with or without a hint (3.e.i)
Ciphertext formWord spaces kept (3.e.i.(1))Same
Random alphabet elsewhereNot used: Patristocrats are K1 only, Xenocrypts use a K1 English keyword alphabetNot used: Patristocrats are K1 or K2, Xenocrypts use K1 or K2
Keyword answersNo keyword option in Division BAllowed only for K1, K2 and K3 Aristocrats (3.e.ii); a random alphabet has no keyword, so you decode the message
No self-decryptionNo letter decrypts to itself (3.g)Same
Timed first questionAlways an Aristocrat with spaces (3.h.i)Same
Special bonusNever: Aristocrats, Patristocrats and Xenocrypts are excluded (3.i)Same
Scoring2 or fewer errors = full credit, then −100 per extra error, floor 0 (4.d)Same

The event itself is the same in both divisions: a team of up to 3, about 50 minutes, on a written or computer-based exam. You bring only writing utensils. No notes, binders or calculators of any kind are allowed; the only reference is the resource sheet the event supervisor hands to each team member, which includes English and Spanish letter-frequency tables as needed for the questions on that exam. The single-sided packet can be split among partners.

How the cipher is built

A key for a random Aristocrat is a permutation of the alphabet. Write the 26 plaintext letters in order, then write the 26 cipher letters under them in some random order. Each plaintext letter is paired with exactly one cipher letter, and no two plaintext letters share a cipher letter. That makes the mapping a one-to-one correspondence.

The rules add one constraint on the key: no plaintext letter may be paired with itself. A cipher letter X can never stand for plaintext X. This is a generation rule, but it is also a solving tool, because it eliminates guesses.

Encrypting step by step

  1. Write the key as a 26-letter table: plaintext A to Z on top, a random arrangement of A to Z underneath. Check that every cipher letter appears exactly once in the bottom row, and that no letter sits under itself.
  2. Split the message into words and keep the spaces exactly as they are.
  3. Replace each letter with the letter directly under it in the table.
  4. Keep any punctuation in place unless the exam says otherwise.
  5. Check the result: decrypt one word with the inverse table and confirm you get the original back.

Worked example. To keep the table easy to check, this guide uses a keyboard-order row as its "random" key; a real exam key will look more scrambled, but the method is identical. Key: A→Q, B→W, C→E, D→R, E→T, F→Y, G→U, H→I, I→O, J→P, K→A, L→S, M→D, N→F, O→G, P→H, Q→J, R→K, S→L, T→Z, U→X, V→C, W→V, X→B, Y→N, Z→M. Written as a table (read each pair top to bottom):

PlainCipherPlainCipherPlainCipher
AQJPSL
BWKATZ
CELSUX
DRMDVC
ETNFWV
FYOGXB
GUPHYN
HIQJZM
IORK

Encrypt TRY THE DOOR AGAIN one word at a time:

Plaintext wordLookupsCiphertext word
TRYT→Z, R→K, Y→NZKN
THET→Z, H→I, E→TZIT
DOORD→R, O→G, O→G, R→KRGGK
AGAINA→Q, G→U, A→Q, I→O, N→FQUQOF

The ciphertext is ZKN ZIT RGGK QUQOF. Notice that the two O's both become G, and the two A's both become Q.

Decrypting step by step

Decryption uses the inverse table. When you have the key, invert it once and use the inverse for the whole message. When you do not have the key, you build the inverse yourself while solving, and the next section covers that.

  1. Build the inverse table: for each cipher letter, write the plaintext letter it came from.
  2. Split the ciphertext into words and keep the spaces.
  3. Replace each cipher letter with its inverse.
  4. Read the result. If it is not English, check whether you used the plaintext row where you needed the cipher row.
  5. Recheck the no-self rule. A decoded letter that equals its cipher letter means one of your lookups is wrong.

Worked example. Decrypt RG OZ FGV with the same key. Inverse lookups: R→D, G→O, O→I, Z→T, F→N, V→W.

Ciphertext wordLookupsPlaintext word
RGR→D, G→ODO
OZO→I, Z→TIT
FGVF→N, G→O, V→WNOW

The plaintext is DO IT NOW.

Solving under tournament conditions

You will not have the key. You will have a ciphertext, a sheet of English letter frequencies, and the exam's time limit. The strongest clues in a random Aristocrat come from the spacing, so start there, and only then bring in frequency.

Here is a message encrypted with the key above and handed to you with no key: ZIT EQZ LQZ GF ZIT DQZ.

StepClueWhat it gives you
1Word shapes: five three-letter words, one two-letter word, and ZIT repeatsA repeated three-letter word is a likely candidate for a very common word such as THE
2EQZ, LQZ and DQZ all end in the same two letters, QZA shared ending suggests an -AT ending, so Q→A and Z→T
3ZIT repeats, and its first letter Z is already TA repeated three-letter word beginning with T is almost certainly THE, so I→H and T→E
4E and H are now taken as plaintext valuesAny -AT word using them is ruled out for the other words, so each of the three needs a different first letter, such as C, M or S
5Plaintext can be checked against the restEQZ→CAT (E→C), LQZ→SAT (L→S), DQZ→MAT (D→M), GF→ON (G→O, F→N)

The final table is Z→T, I→H, T→E, E→C, Q→A, L→S, D→M, G→O, F→N, which decodes to THE CAT SAT ON THE MAT.

Three habits help most:

  • Scan for word shapes before writing anything. One-letter words are almost always A or I, and two-letter words are often OF, TO, IN, IT, IS, ON, AS, AT or BE. Mark likely letters in pencil, because a wrong guess costs time.
  • Use apostrophes and doubled letters. A doubled cipher letter inside a word (like GG in RGGK) stands for a doubled plaintext letter, most often LL, EE, SS, OO or TT. An apostrophe inside a word tells you a contraction is likely, such as I'M, DON'T or IT'S.
  • Keep one table, and fill it steadily. Each confirmed letter should go into a single cipher-to-plain table. When a new guess conflicts with the table, the guess is wrong, not the table.
Bar chart of the relative frequency of each letter in English text, with E the tallest bar and Z, Q and X among the shortest.
The shape to remember for a long message. Use it to rank candidates after the word-shape clues, not as the first step.Credit: Nandhp, Public domain, via Wikimedia Commons · source

Timing and scoring

The 2027 rules score a random Aristocrat like any other regular question: the final score is exam score + timing bonus + special bonus (rule 4.b). An Aristocrat can earn the timing bonus when it is the timed first question, but it can never count toward the special bonus, which is reserved for questions that are not Aristocrats, Patristocrats or Xenocrypts.

Common pitfalls

  • Breaking the one-to-one mapping

    Two plaintext letters can never share a cipher letter, and one cipher letter can never stand for two plaintext letters. If your table forces this, one of the guesses is wrong; find it before you continue.

  • Forgetting the no-self rule

    A decoded letter must never equal its cipher letter. Use the rule to rule out words: if a guess would require a cipher letter to decode to itself, discard it.

  • Writing before the start signal

    Rule 3.c forbids opening the packet or writing before the start signal, or writing after the stop signal.

How tournaments test this

There are no archived tournament questions tagged as random Aristocrats to count, so this guide does not quote frequencies. What the 2027 rules fix is:

  • The first question on every exam is a spaced Aristocrat and is timed, and a random alphabet is one of the alphabets it may use. Fast random-Aristocrat solving is worth up to 1,200 timing-bonus points (solving at 0 seconds), and every 10 seconds saved is worth 20 points.
  • The cipher is available at Regional, State and National tests in both divisions, because every Regional code type carries forward.
  • Random alphabets always require the decoded message. Division C's keyword option does not apply to them.
  • An Aristocrat can never be a special bonus question. Those slots go to other ciphers, and in 2027 at least one of them must be a Homophonic cipher.

Log each practice solve with its time, error count and the clue that cracked it.

Practice ciphertexts

Solve these without the key. Each one uses the same key as the worked examples above, so once you find a couple of letters you can check the whole table.

References and further reading

See also