AES Encryption / Decryption

🔒 AES Encryption / Decryption – Browser-Based AES Tool

The Advanced Encryption Standard (AES) is the most widely adopted symmetric-key block cipher in the world, standardized by NIST in 2001 (FIPS 197). It is used in virtually every secure communication system — from TLS/HTTPS and Wi-Fi (WPA2/WPA3) to full-disk encryption and secure messaging apps. This tool lets you encrypt and decrypt text using AES entirely in your browser, with no data ever sent to a server.

🔑 Key Sizes: 128, 192, and 256 Bits

AES operates on fixed-size 128-bit blocks but supports three key lengths, each offering a different security level:

• AES-128 — 128-bit key (16 bytes), 10 rounds. Excellent performance and strong security; used in many consumer applications and TLS connections.
• AES-192 — 192-bit key (24 bytes), 12 rounds. Rarely used in practice but provides a higher security margin.
• AES-256 — 256-bit key (32 bytes), 14 rounds. The gold standard for high-assurance encryption. Required for protecting classified information at SECRET/TOP SECRET levels (NSA Suite B). Recommended for most new systems.

⚙️ Supported Cipher Modes

AES is a block cipher, meaning it encrypts data in 128-bit (16-byte) chunks. A cipher mode of operation defines how these blocks are processed sequentially:

AES-CBC (Cipher Block Chaining)

CBC is the most widely used AES mode for general-purpose encryption. Before each block is encrypted, it is XORed with the previous ciphertext block — starting with the Initialization Vector (IV) for the first block. This chaining ensures that identical plaintext blocks produce different ciphertext blocks, hiding data patterns. CBC requires PKCS#7 padding to fill the last block to 128 bits. Use AES-256-CBC for file encryption, database field encryption, and most server-side cryptography where GCM is not available.

AES-GCM (Galois/Counter Mode) — Recommended

GCM combines AES in CTR mode with the GHASH authentication function to deliver Authenticated Encryption with Associated Data (AEAD). In addition to the ciphertext, it produces a 128-bit authentication tag that lets the decryptor verify that the data has not been tampered with. GCM is fully parallelizable on both encryption and decryption, making it fast on modern CPUs with hardware AES support. It is the default mode in TLS 1.3, SSH, and most modern cryptographic protocols. Use a 96-bit (12-byte) nonce as recommended by NIST SP 800-38D — never reuse a nonce with the same key.

AES-CTR (Counter Mode)

CTR turns AES into a stream cipher by encrypting successive counter values and XORing the output keystream with the plaintext. It requires no padding, handles arbitrary-length plaintext, and supports full parallel encryption and decryption. CTR is widely used in disk encryption and network protocols. The counter must never be reused with the same key — doing so completely breaks confidentiality.

⚠️ AES-ECB (Electronic Codebook) — Avoid

ECB encrypts each 128-bit block independently with no chaining or randomization. Because identical plaintext blocks always produce identical ciphertext blocks, structural patterns in the data remain visible in the ciphertext. The famous "ECB penguin" — an image of Tux the Linux mascot that remains recognizable after ECB encryption — illustrates this flaw. Do not use ECB for any sensitive data. It is provided here for educational and compatibility purposes only.

🧪 How to Use This Tool

1. Choose Encrypt or Decrypt mode.
2. Select a Cipher Mode (CBC, GCM, or CTR), a Key Size (128/192/256-bit), and the desired Output Format (Base64 or Hex).
3. Enter your Secret Key. You can provide it as plain text (auto-padded), hexadecimal, or Base64-encoded bytes.
4. Enter or generate an IV / Nonce. Click 🎲 Random to generate a cryptographically secure random value.
5. Paste or type your plaintext (for encryption) or ciphertext (for decryption) in the input area and click the action button.
6. For GCM encryption, copy and save the displayed Auth Tag — it is required to verify integrity during decryption.

📐 Key and IV Size Reference

🔐 Security Best Practices

• Prefer AES-GCM over CBC or CTR whenever possible — authenticated encryption prevents ciphertext tampering and padding oracle attacks.
• Never reuse an IV/nonce with the same key. Each encryption operation must use a fresh, randomly generated IV.
• Use AES-256 for long-term data protection and AES-128 where performance is critical.
• Avoid ECB mode entirely for any real data — use it only for academic study.
• This tool uses the browser's built-in Web Crypto API (window.crypto.subtle), which provides hardware-accelerated, standards-compliant AES — the same API used by production applications.

💡 Common Use Cases

• Testing and validating AES implementations in your software projects
• Learning about symmetric encryption, block cipher modes, and IV usage
• Encrypting configuration snippets or small secrets for storage
• Generating and verifying encrypted payloads for API or local storage testing
• Educational exploration of how key size and cipher mode affect ciphertext

All operations run 100% locally in your browser using the Web Crypto API. No data is transmitted to any server. For production applications, use a well-tested cryptography library and follow your platform's security guidelines.