AES Encrypt and Decrypt

About AES encrypt and decrypt

This tool encrypts a piece of text with AES in GCM mode using a passphrase you choose, and decrypts it again later. It derives the key with PBKDF2 and produces one Base64 string that carries everything except the passphrase, so it suits sending a short secret through a channel you do not trust.

How to use it

1. Choose Encrypt or Decrypt at the top.
2. Paste your text into Plaintext, or the Base64 payload into Encrypted payload (Base64).
3. Enter the Passphrase, then set AES key size and, when encrypting, PBKDF2 iterations.
4. Select the Encrypt or Decrypt button, then copy the result with Copy result. Clear empties both boxes.

A real round trip at 100,000 iterations

Plaintext: Meet at noon, passphrase: correct horse, AES-256-GCM

AQABhqCNM+d8N0FlU9gHcGeIQaiJE7PZkZ57SnHgyOdY1D0SgKXAvbvNf16lXYh9aHhOJOICo4F9PfZjbQ== (your output will differ because salt and IV are random)

When to use it

• Passing a database password or recovery code to a colleague through chat, with the passphrase sent separately.
• Storing a short note in a shared document so only people who know the passphrase can read it.
• Learning how a versioned, self-describing encrypted blob is put together.
• Checking that your own AES-GCM and PBKDF2 code interoperates with the payload layout described in the first answer below.

Questions about AES encrypt and decrypt

What exactly is inside the Base64 payload?

One version byte, the iteration count as a 4-byte number, a 16-byte random salt, a 12-byte random IV, then the ciphertext followed by GCM's 16-byte authentication tag. Nothing but the passphrase needs to be kept.

Why does decryption say the passphrase is wrong or the payload was modified?

GCM authenticates the data, and a wrong key, a changed byte, or a different AES key size all fail the same check. The design intentionally does not reveal which one it was.

Do I need to remember the key size?

Yes. The iteration count is read from the payload, but the AES key size is not stored, so decryption must use the same AES-128, AES-192 or AES-256 setting as encryption.

Is a reused IV a problem?

Repeating an IV with the same key breaks GCM's security. Every encryption here draws a new random salt and IV, so the derived key and IV combination is unique each time.

How strong is the result?

The cipher is AES-GCM, which is sound, but the passphrase is the weak point. Choose a long, random passphrase and higher iterations, since an attacker can guess offline without ever touching this page.

Related tools

• PBKDF2 key generatorDerive a cryptographic key from a password using PBKDF2 with a configurable salt, iteration count, hash and key length.
• Passphrase generatorGenerate memorable Diceware-style passphrases with a live strength estimate.
• MD5 GeneratorGenerate an MD5 hash from text
• SHA GeneratorGenerate SHA-1, SHA-256, SHA-384, and SHA-512 hashes
• Bcrypt GeneratorGenerate a bcrypt hash from text
• JWT DecoderDecode and inspect JWT tokens — view header, payload claims, expiry, and signature.