ForHosting KIT · Developer Utilities

Running-key cipher

This running-key cipher tool encrypts or decrypts text with a classical polyalphabetic substitution that uses a long passage of key text as a non-repeating key stream, not a short keyword that wraps.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Each alphabetic letter in the message is shifted by the next letter taken from the key passage, so the same plaintext letter can map to different ciphertext letters depending on position while the key never cycles back on itself. Only A–Z characters move: modular arithmetic on a twenty-six letter ring preserves case, and spaces, digits, punctuation, and other symbols pass through without consuming a key step. If the key passage has fewer letters than the message, the engine reports that the key is too short instead of silently wrapping like ordinary Vigenère. The path is fully deterministic with no network calls, no random salts, and no date-dependent shortcuts, so teaching fixtures and CI goldens stay bitwise stable. Use it free in the browser for CTF warm-ups, history-of-crypto lessons, and book-cipher style demos, or call the API at $0.002 per successful request when pipelines need reproducible running-key transforms.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/enc/running-key

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/enc/running-key \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"text":"Attack at dawn","key":"It was the best of times"}'

const res = await fetch("https://api.kit.forhosting.com/enc/running-key", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "text": "Attack at dawn",
    "key": "It was the best of times"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/enc/running-key",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "text": "Attack at dawn",
    "key": "It was the best of times"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/enc/running-key", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"text":"Attack at dawn","key":"It was the best of times"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"text":"Attack at dawn","key":"It was the best of times"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/enc/running-key", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "text": "Attack at dawn",
  "key": "It was the best of times"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "enc.running_key",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →