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  • K1 Patristocrat (Keyed Plain Alphabet, No Spaces)
  • What it is
  • Alphabet construction (K1)
  • How decryption works (K1, no spaces)
  • Solving method (Patristocrat specifics)
  • Worked mini example
  • Common pitfalls
  • Quick reference
  • Practice
  • Answers

Codebusters - K1 Patristocrat

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Type: Inquiry
Divisions: B, C
Participants: Up to 3
Approx. Time: 50 minutes
Allowed Resources: Writing utensils; up to three Class I or Class II calculators. No external notes. Supervisor provides scratch paper and reference sheet.

K1 Patristocrat (Keyed Plain Alphabet, No Spaces)

What it is

K1 Patristocrat is a monoalphabetic substitution with a keyed PLAINTEXT alphabet (top row) and a normal A–Z CIPHERTEXT alphabet (bottom row), exactly like K1 Aristocrat—but the ciphertext removes spaces/punctuation and is often grouped visually (e.g., groups of 5). You must infer word boundaries from language while maintaining a one-to-one letter mapping.

  • Top row: keyed plain alphabet (keyword deduped, then unused A–Z).
  • Bottom row: A–Z.
  • Decrypt: for ciphertext C, find index i in A–Z (bottom) → output top[i].

Alphabet construction (K1)

Build the keyed plain alphabet from the keyword (dedupe, then append unused A–Z).

Example keyword: SCIENCE → dedup SCIEN; remaining ABDFGHJKLMOPQRTUVWXYZ Top (plain):

S C I E N A B D F G H J K L M O P Q R T U V W X Y Z

Bottom (cipher):

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

How decryption works (K1, no spaces)

  1. Build or recover the top row (keyed plain).
  2. For each C, index i = position of C in A–Z; output top[i].
  3. Insert spaces by language patterns; grouping is cosmetic.

Solving method (Patristocrat specifics)

  1. Mapping table: maintain consistent P↔C pairs (bijective). Use digrams/trigrams, double letters, and suffixes (-ING, -ED, -ER, -LY) since spaces are absent.
  2. Reconstruct top row: place A–Z on bottom; above each cipher letter C place its plaintext P at index(C). The top row will show a keyword prefix then the A–Z tail.
  3. Keyword: read the top row’s prefix (deduped) before the alphabetical continuation.
  4. Segmentation: add provisional spaces where words naturally form; keep only mappings that remain globally consistent.

Worked mini example

Given a run like ETTXEFEXTTPX…, map each C to P via top row and insert spaces when common words emerge. Iterate mapping and segmentation together.

Common pitfalls

  • Treating 5-letter blocks as word boundaries.
  • Forcing a keyword that contradicts the reconstructed row.
  • Allowing duplicate P for different C (or vice versa).

Quick reference

  • K1: top keyed plain; bottom A–Z.
  • Decrypt: index(C in A–Z) → top[i].
  • Spaces are inferred; grouping is cosmetic.

Practice

  1. From 10 letter pairs, complete the K1 top row and propose a deduped keyword.
  2. Decrypt a 5-grouped ciphertext and segment into words.

Answers

  1. Completed rows vary; validate by (a) permutation of A–Z, (b) keyword prefix followed by A–Z tail, (c) re-encrypt check passes.
  2. Segmentation aligns with common words (THE/AND/OF/TO/ING/ED) and retains mapping consistency across the entire text.