---
title: "Cryptoquote"
id: 76385
type: "computer_media"
slug: "cryptoquote"
url: "http://localhost/computer_media/cryptoquote/"
markdown_url: "http://localhost/computer_media/cryptoquote.md"
published_at: "2026-11-11T08:02:47+00:00"
modified_at: "2026-11-11T08:02:47+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2026/11/cryptoquote-1.png"
excerpt: "Decode a newspaper-style cryptoquote with your ZX80's help: it shows the letter frequencies and redraws the puzzle as you substitute letters."
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "ZX80"
    slug: "zx80"
    taxonomy: "post_tag"
    url: "http://localhost/tag/zx80/"
model:
  - name: "Sinclair ZX80"
    slug: "zx80"
    taxonomy: "model"
    url: "http://localhost/model/zx80/"
genre:
  - name: "Game"
    slug: "game"
    taxonomy: "genre"
    url: "http://localhost/type/game/"
media_type: "Program"
download_url: "https://archive.org/download/timex-sinclair-software-archive/Cryptoquote%20%281980%29%28-%29%28ZX80%29%28US%29%28Program%29.zip"
mediadate: "1980"
images:
  - url: "http://localhost/wp-content/uploads/2026/11/cryptoquote-1.png"
  - url: "http://localhost/wp-content/uploads/2026/11/cryptoquote-2.png"
article_media:
  - id: 19200
    title: "Cryptoquote — Use Your ZX80 to Help You Solve Substitution Ciphers"
    type: "article"
    url: "http://localhost/article/cryptoquote-use-your-zx80-to-help-you-solve-substitution-ciphers/"
related_content:
  - id: 19209
    title: "How to Wire a Big Keyboard"
    type: "article"
    url: "http://localhost/article/how-to-wire-a-big-keyboard/"
  - id: 19898
    title: "Dear Editor"
    type: "article"
    url: "http://localhost/article/dear-editor-33/"
media_type_tags: "Game"
license: false
---

# Cryptoquote

A helper for solving substitution ciphers on a 1K ZX80. The program prints the coded quotation with a dash under each letter you have not yet solved. Answer COMMAND with F to see how often each letter occurs, or with X=L to say that the coded letter X stands for L; the quotation is reprinted with every solved letter filled in. The article lists the usual frequency order of English letters, ETAONRISHDLFCMUGYPWBVKXJQZ, as a starting point.

To set a new puzzle, change the quotation in line 990, keeping it no longer than the one printed so the display fits in 1K. The answer to the printed puzzle appeared in the next issue.

Published in Syntax November 1980 ([Cryptoquote — Use Your ZX80 to Help You Solve Substitution Ciphers](https://timexsinclair.com/article/cryptoquote-use-your-zx80-to-help-you-solve-substitution-ciphers/)).

## Source Code

```
   6 DIM T(25)
   7 LET K=1000
  60 FOR X=0 TO 25
  65 LET T(X)=220
  70 NEXT X
 100 CLS
 110 GO SUB 990
 120 PRINT T$
 123 LET X=CODE(T$)
 125 IF X<38 OR X>63 THEN GO TO 170
 130 PRINT CHR$(T(X-38));
 140 LET T$=TL$(T$)
 160 GO TO 123
 170 IF X=1 THEN GO TO 200
 175 PRINT CHR$(X);
 180 GO TO 140
 200 PRINT
 205 PRINT "COMMAND:";
 210 INPUT F$
 220 IF CODE(TL$(F$))=227 THEN LET T(CODE(F$)-38)=CODE(TL$(TL$(F$)))
 222 IF F$="F" THEN GO TO 400
 240 GO TO 100
 400 CLS
 410 GO SUB 990
 460 LET N=CODE(T$)-38
 470 IF N=-37 THEN GO TO 500
 480 IF N<0 OR N>25 THEN GO TO 485
 483 LET T(N)=T(N) + K
 485 LET T$=TL$(T$)
 490 GO TO 460
 500 FOR X=0 TO 12
 505 LET S=T(X)-(T(X)/K)*K
 506 LET S2=T(X+13)-(T(X+13)/K)*K
 510 PRINT CHR$(X+38);"(";CHR$(S);"):";T(X)/K;" ";CHR$(X+51);"(";CHR$(S2);"):";T(X+13)/K
 520 LET T(X)=S
 525 LET T(X+13)=S2
 530 NEXT X
 540 GO TO 200
 990 LET T$="UVQ JVQQXZX KQ JQYGZKZ UBKV YWJVBPZX WJJZGKX KVZ JQPMBKBQPX QC XFWDZLH"
 999 RETURN
```