Patristocrat cipher

What the Patristocrat cipher is

Both ciphers are monoalphabetic substitutions: one plaintext letter always becomes the same ciphertext letter, and in the tournament versions no letter stands for itself. The difference is what is left visible. An Aristocrat keeps the word breaks and the punctuation, so a solver can see that a three-letter word might be THE, or that an apostrophe is followed by S or T. A Patristocrat removes all of that and regroups the letters in fives, so the only structure left is the letters themselves.

The names come from the American Cryptogram Association, whose members have set and solved these puzzles for generations; the Association uses Aristocrat for the spaced form and Patristocrat for the unspaced one, and both appear in its catalogue of pencil-and-paper types. Codebusters borrowed the vocabulary along with the conventions, including the K1 alphabet, in which the plaintext row is built from a keyword and the ciphertext row is a shifted straight alphabet.

Solving one is frequency work. A tally of the ciphertext letters gives the shape: in English text of any length E is usually the commonest, then T, A, O, I and N. Doubled letters narrow the options, since English doubles a short list of letters, and a three-letter run that repeats is a good candidate for THE or AND. Each guess is pencilled in everywhere its letter appears, and the solver reads straight across the group breaks looking for runs that sound like English.

The mistakes come from the missing breaks. A student who treats a group of five as a word wastes the first minutes, and one who commits to a guess without checking it across the whole message can fill half the alphabet wrong. Tallying first, guessing in pencil, and testing each guess in two or three places before trusting it keeps the work honest. With a K1 alphabet, the keyword starting to show in the plain row is the sign the solve has turned the corner.

How to solve a Patristocrat cipher

A letter-for-letter substitution, as in an Aristocrat, with the word breaks and punctuation taken out and the letters printed in groups of five that have nothing to do with the words. No letter stands for itself. Without word shapes to lean on, letter counts do most of the work.

1. Tally every ciphertext letter. The commonest few are probably among E, T, A, O, I and N.
2. Look for doubled letters, which in English are often EE, LL, SS, OO or TT, and for a three-letter run that repeats: THE is the commonest, and its middle letter is rarer than its ends.
3. Pencil one guess in everywhere its letter appears and read straight across the group breaks. A wrong guess turns the runs unpronounceable within a few letters.
4. No letter stands for itself, so every position has one option crossed out before you begin.
5. With a K1 alphabet, fill the plain row as you go; once the keyword shows at its start, the rest of the row follows in alphabetical order. Put the word breaks back last.

A worked example

Decode TRISH WSGGK ROMNH (K1 keyword COMET)

The plain row starts with the keyword; the cipher row is the alphabet, starting from D:
Plain:  C O M E T A B D F G H I J K L N P Q R S U V W X Y Z
Cipher: D E F G H I J K L M N O P Q R S T U V W X Y Z A B C

Find each ciphertext letter in the cipher row and read the letter above it:
T → P   R → L   I → A   S → N   H → T   W → S   G → E   G → E
K → D   R → L   O → I   M → G   N → H   H → T

Letters: PLANTSNEEDLIGHT. The doubled GG was the EE of NEED.
Plaintext: PLANTS NEED LIGHT

Patristocrat in Codebusters

Among the Science Olympiad rule sets OlyPrep has read, the Patristocrat is on the Division B Codebusters list and not on the elementary lists. The Division B rules OlyPrep has read describe it as an Aristocrat with the spaces removed, printed in groups of five, under a K1 alphabet in which no letter maps to itself. Scoring follows the paper’s usual rule, by letters, with a decoded message of up to two wrong letters commonly counted as solved.

Because it is harder than an Aristocrat, a Patristocrat is often worth more points on a paper, and teams commonly give it to whoever is quickest at frequency work. The Division B rules OlyPrep has read also keep it, with the Aristocrat and the Xenocrypt, out of the special-bonus questions, so its value is the question’s own.

The lab below draws a science sentence, builds a K1 alphabet from a keyword on its own list with a shift that leaves no letter in place, and prints the ciphertext in groups of five. The key line prints the keyword and both alphabet rows; a student practising the real thing covers it and uses it to check. The easy setting uses a short sentence and the hard setting a long one, and the longer message is the one frequency work finds easier. Check compares letters only, exactly; Reveal shows the plaintext.

Practice the Patristocrat cipher

The lab below is set to the Patristocrat cipher alone. Pick a difficulty, generate a challenge, decode it, then check your answer or reveal the solution. It runs in your browser, needs no account, and is unlimited on every OlyPrep plan.

Where the Patristocrat cipher is tested

The Science Olympiad rule sets OlyPrep has read that name this cipher:

• Science Olympiad Division B — on the Codebusters list, under a K1 alphabet

Cipher lists change with each season’s rules; a tournament’s own rulebook is the authority on what it tests.