AES-256 Encryptor

A simple, secure, and fast client-side encryption tool.
Your data never leaves your browser.

Encrypt Text Decrypt Text
AES-256-GCM • PBKDF2 • Open Source

About This Tool

The AES-256 Encryptor/Decrypter is a simple, open-source, completely client-side web utility created for one purpose: letting you encrypt and decrypt text securely without ever sending your data anywhere. Built with modern browser cryptography and deployed as a static site, it guarantees that your plaintext, passphrase, and resulting ciphertext never leave your device.

At the heart of the tool lies AES-256 in Galois/Counter Mode (GCM) — the same encryption standard trusted by governments, banks, and security professionals worldwide. AES-256 uses a 256-bit key, offering an astronomical number of possible combinations that renders brute-force attacks infeasible even with future quantum advances in classical computing. GCM mode goes further by providing built-in authentication: every encrypted message includes a cryptographic tag that verifies integrity. If even one bit is altered — accidentally during copy-paste or maliciously — decryption fails immediately with a clear error message.

To turn your chosen passphrase into a secure 256-bit key, the tool uses PBKDF2 (Password-Based Key Derivation Function 2) with SHA-256 hashing, 100,000 iterations, and a fresh 16-byte random salt generated for every encryption. This combination slows down offline password-guessing attacks dramatically while ensuring that identical passphrases produce different keys when salts differ. A unique 12-byte random initialization vector (IV) is also created each time, preventing any pattern analysis across multiple encryptions of similar content.

Everything runs through the Web Crypto API, a carefully audited, native browser interface available in Chrome, Firefox, Edge, and Safari. No external libraries handle the cryptography — only browser-native code — which means no supply-chain risks from third-party packages. The maximum input size of 1,000,000 characters accommodates long documents, journal entries, email drafts, or configuration files while still completing operations in seconds on modern hardware.

Because the site is fully static (hosted on GitHub Pages with no backend, database, or server-side logic), there is literally nowhere for your data to be sent. No analytics scripts, no tracking pixels, no cookies, no localStorage persistence beyond the current tab session. When you close or refresh the page, all memory is released. This architecture makes the tool suitable for highly sensitive use cases where trust in remote services is unacceptable.

Our mission is straightforward: give individuals powerful, standards-compliant encryption without asking for trust, accounts, or internet connectivity beyond the initial page load. The source code is open on GitHub so anyone can audit, fork, or self-host it. Privacy is not a feature here — it is the entire design.

Last updated: February 2026

How to Use the AES-256 Encryptor

1. Enter Your Text

Paste or type the sensitive content you want to protect into the large textarea on the Encrypt page. The tool accepts up to 1,000,000 characters — enough for long documents, notes, or email drafts. Special characters, Unicode, and multiple languages are fully supported via UTF-8 encoding.

2. Choose a Strong Passphrase

Enter a passphrase of at least 8 characters (longer is much better). This is the only secret you provide. The tool derives a 256-bit AES key from it using PBKDF2 with a random salt and 100,000 iterations. Never reuse passphrases across different messages. A password manager is highly recommended for generating and storing long, unique phrases.

3. Encrypt & Copy

Click "Encrypt Now". Within seconds you receive a single base64 string containing the salt, IV, ciphertext, and GCM authentication tag. Copy this string and store it securely (text file, encrypted drive, etc.). The original text is automatically cleared from the input field for safety.

4. Decrypt Later

On the Decrypt page, paste the exact base64 ciphertext and the same passphrase. Click "Decrypt Now". If everything matches, you see your original text. If the passphrase is wrong, ciphertext is corrupted, or data was tampered with, you receive an immediate authentication failure message — no partial or incorrect output is ever shown.

Key rule: Keep the passphrase secret and separate from the ciphertext. Never send them together over the same channel. Test decryption immediately after encryption to confirm success before relying on the protected data.

Frequently Asked Questions

No. Every operation — key derivation, encryption, decryption — happens exclusively in your browser using the Web Crypto API. There is no backend, no database, no logging, and no data transmission. The site is purely static HTML, CSS, and JavaScript hosted on GitHub Pages.

Nothing can recover the data. AES-256-GCM with proper key derivation is designed to be unbreakable without the exact passphrase. There is no "forgot password" mechanism because we never store or have access to your key material. Choose and store passphrases securely (password manager, physical safe backup, etc.).

Extremely secure when used correctly. AES-256 is a NIST-standard symmetric cipher with no known practical attacks against properly implemented 256-bit keys. GCM mode adds authenticated encryption, protecting against both eavesdropping and tampering. Security ultimately depends on passphrase strength — a long, random passphrase (20+ characters or 5–6 word diceware) makes brute-force infeasible for decades or centuries.

Most common causes: typo/case sensitivity in passphrase, extra spaces, clipboard corruption, truncated ciphertext during copy-paste, or using a different browser/device that handles Web Crypto slightly differently (very rare). Always test decryption right after encryption and double-check the full base64 string.

Yes — after the first load, the site works offline (service worker/cache permitting). All crypto logic is self-contained. For maximum security, download the source and run it locally or self-host.

Yes — the entire project is open-source on GitHub under MIT license. You can review, fork, modify, or self-host the code yourself. No obfuscation or closed components are used.