ForHosting KIT · Developer Utilities

Vigenère cipher encoder and decoder

This Vigenère cipher tool encrypts or decrypts text with the classic polyalphabetic substitution that uses a repeating keyword to choose a different Caesar shift for each letter.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Unlike a single fixed Caesar offset, the key stream walks through the keyword so the same plaintext letter can map to different ciphertext letters depending on position, which is the historical strength of the method for classroom demos and puzzle design. Only alphabetic characters move: each A–Z letter is shifted by the matching key letter with modular arithmetic on a twenty-six letter ring, case is preserved, and spaces, digits, punctuation, and other symbols pass through without consuming a key step. The engine is fully deterministic with no network calls, no random salts, and no date-dependent shortcuts, so goldens and teaching fixtures stay bitwise stable. A standard check is Attack at dawn with key LEMON encrypting to a known ciphertext that decrypts back under the same keyword. Use it free in the browser for CTF warm-ups, history-of-crypto lessons, and reversible puzzle worksheets, or call the API at $0.002 per successful request when pipelines need reproducible Vigenère transforms in CI and backend services.

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/vigenere

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/vigenere \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"text":"Attack at dawn","key":"LEMON"}'

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

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/enc/vigenere",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "text": "Attack at dawn",
    "key": "LEMON"
},
)
task_id = res.json()["task_id"]

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

body := bytes.NewBufferString(`{"text":"Attack at dawn","key":"LEMON"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/enc/vigenere", 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": "LEMON"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "enc.vigenere",
  "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 →

Run — free