AES-256-GCM Utility

A professional, client-side tool for high-security encryption and decryption.

Security First: All operations run locally in your browser.
Generate Key
Encrypt Data
Decrypt Data

About This AES-256-GCM Utility

A simple, powerful, fully client-side AES-256-GCM authenticated encryption tool built for privacy-conscious users.

This utility lets you encrypt and decrypt text messages using AES-256 in Galois/Counter Mode (GCM) — the same authenticated encryption algorithm trusted by TLS 1.3, secure messaging protocols, and modern file encryption standards. All operations run exclusively in your browser via the Web Crypto API — no data ever leaves your device, no servers are involved, and no tracking occurs.

AES-256-GCM provides two essential protections in one efficient pass:

  • Confidentiality — your plaintext is transformed into unreadable ciphertext using a 256-bit key and a unique nonce.
  • Integrity & authenticity — an authentication tag verifies that the message has not been tampered with. If even one bit is changed, decryption fails with an error.

Key features include:

  • Client-side PBKDF2 key & nonce derivation from any passphrase you choose (for convenience/testing only — not recommended for high-security use)
  • Realtime input validation (key = 64 hex chars, nonce = 24 hex chars)
  • Support for messages up to 1,000,000 characters (~1 MB)
  • Clear warnings about nonce reuse, weak keys, and deterministic derivation risks
  • Responsive Bootstrap interface with dark mode support
  • Copy-to-clipboard buttons for easy transfer of keys, nonces, and ciphertext

This tool is ideal for developers, security enthusiasts, privacy advocates, or anyone who wants to experiment with strong authenticated encryption without trusting third-party servers. It is not a replacement for dedicated password managers or production-grade cryptographic libraries — always follow best practices (random keys, never reuse nonces) when protecting real sensitive data.

Open-source · No analytics · No tracking · Runs 100% in your browser

How to Use This Tool

1
Generate Key & Nonce (Optional)

Go to the Generate tab. Enter any memorable phrase or long text. The tool uses PBKDF2 (SHA-256, 100,000 iterations) to deterministically derive a 64-character hex key (256 bits) and 24-character hex nonce (96 bits). Copy both values. Remember: same phrase → same output every time.

2
Encrypt Your Message

Switch to the Encrypt tab. Paste or type your plaintext (up to 1 MB). Enter your 64-hex key and 24-hex nonce. Click Encrypt. The output is base64-encoded ciphertext + authentication tag. Copy the full string and store it securely.

3
Decrypt When Needed

Go to the Decrypt tab. Paste the full base64 output from step 2. Enter the exact same key and nonce used for encryption. Click Decrypt. If the tag verifies, you’ll see your original plaintext. If anything is wrong, you’ll get a clear error.

4
Security Reminders

Never reuse the same nonce with the same key. Use truly random keys for important data (not derived phrases). Test decryption immediately after encryption. Keep backups of important ciphertext + key/nonce pairs.

Important: This is an educational / personal-use tool. For production-grade security, use audited libraries and follow strict key management practices.

Frequently Asked Questions

No. Every operation — encryption, decryption, key derivation — happens entirely in your browser using the Web Crypto API. Nothing is transmitted, logged, or stored remotely.

Your encrypted data becomes permanently unrecoverable. There is no backdoor, recovery service, or server-side storage. Always keep secure backups of your key/nonce + ciphertext together.

Never. Reusing a nonce with the same key catastrophically breaks security — plaintext can be recovered and forged messages created. Always use a fresh nonce for every encryption.

It is convenient and uses PBKDF2 with 100,000 iterations, but it is deterministic — same phrase always produces the same key/nonce. For serious security, use truly random keys generated by your operating system, not passphrase derivation.

Browser memory constraints and performance. Encrypting/decrypting 1 MB usually takes under 1 second; larger inputs risk slowdowns or tab crashes. For very large files, use dedicated desktop tools.

Yes — after the initial page load. All JavaScript and Bootstrap assets are cached by your browser. You can disconnect from the internet and continue using the tool normally.