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AES GCM Encryptor

This tool lets you encrypt and decrypt in AES-GCM.

AES GCM Encryption Tool​

🔐 AES GCM Encryptor

How to Use AES-GCM Encryption Tool to Send Secret Messages​

1. Agree on a Shared Key (Offline)​

Meet your friend offline and generate a random 32-byte key (256-bit). Don't use wechat, QQ, 163 mail or other unsafe APP to send your key.

Both of you store this securely (e.g., password manager, paper copy).

Example AES key in Base64:

# 16 byte 
MTIzNDU2Nzg5MGFiY2RlZg==

# 32 byte 
YWJjZGVmMTIzNDU2Nzg5MEFCQ0RFRistKi88PiwuPy8=

2. Encrypt the Message (Sender)​

The sender use this AES-GCM encryption tool to encrypt your message.

Input:

  • Shared Key (base64 format, 16 or 32 byte)

  • Message text

Output:

Encrypted ciphertext (Base64 encoded)

Send this ciphertext to your friend via email, chat, or any channel (safe even if intercepted). Don't send the key, your friend has already known the key offline.

3. Decrypt the Message (Receiver)​

The receiver use this AES-GCM encryption tool to encrypt your message.

Receiver inputs:

  • The same Shared Key (base64 format, 16 or 32 byte)

The key must be the same key that used to encrypt message.

  • The Ciphertext received

AES-GCM decrypts it and shows the original message.

Example​

Alice and Bob are two friends who want to chat securely. They don’t trust the internet and APPs.

So, they decide to use AES-GCM Encryption Tool to keep their messages safe.

Step 1: Agree on a Secret Key (Offline)

Before using the tool:

Alice and Bob meet in person at a park.

They generate a random 16-byte Base64 key :

MTIzNDU2Nzg5MGFiY2RlZg==

They both write it down safely and promise to keep it secret.

They never send this key online.

This is like agreeing on a shared lock and key before sending letters.

Step 2: Alice Encrypts a Message

Later, Alice wants to send Bob:

Hello, Bob. 近排點呀？

But she doesn’t want anyone else to read it.

She opens the AES-GCM Encryption tool:

She enters the shared key in the "Shared Key" field.

She types her message in "Message to Encrypt".

She clicks Encrypt.

The tool scrambles the message into something unreadable, like:

Sw7+XDDPrzDe1FLtK7nSpcjOU3Xlv1fbRIuRwf5Y21s96/vRJyMsKSV106/t/XE118FgCjy68A==

(If you try to use their key to encrypt the same text, the output may be different, because AES-GCM use a random iv to encrypt, each time you will get an different output.)

This ciphertext is safe to send over email, chat, or even post online. Nobody can read it without the secret key. Alice sends the ciphertext to Bob.

Step 3: Bob Decrypts the Message

Bob receives the ciphertext:

Sw7+XDDPrzDe1FLtK7nSpcjOU3Xlv1fbRIuRwf5Y21s96/vRJyMsKSV106/t/XE118FgCjy68A==

He opens his AES-GCM Encrytion Tool:

He enters the same shared key that Alice gave him offline.

He pastes the ciphertext into "Ciphertext to Decrypt".

He clicks Decrypt.

The tool instantly turns it back into:

Hello, Bob. 近排點呀？

Now Bob knows what Alice said, and Eve (the hacker) learns nothing.

About AES-GCM​

AES (Advanced Encryption Standard) is a widely trusted algorithm used worldwide to encrypt data. It converts readable information (plaintext) into scrambled data (ciphertext), which cannot be understood without the correct secret key.

GCM (Galois/Counter Mode) is a mode of operation for AES that provides:

  • Confidentiality: Your message content is hidden from unauthorized viewers.
  • Integrity & Authentication: Ensures the ciphertext hasn’t been altered or tampered with.
  • Efficiency: Fast and suitable for encrypting short or long messages.

How AES-GCM Works?

  1. Shared Key: Both sender and receiver must agree on the same secret key (usually 256 bits = 32 random bytes).
  2. IV (Initialization Vector): A unique, random value is generated for every message. It ensures that even if you encrypt the same message twice, the ciphertext will look different.
  3. Encryption:
  • The sender combines the plaintext, key, and IV using AES-GCM.
  • The result is ciphertext that cannot be understood without the key.
  • The IV is usually sent alongside the ciphertext (not secret).
  1. Decryption:
  • The receiver uses the same key and extracts the IV from the message.
  • AES-GCM converts the ciphertext back into readable text (plaintext).
  • If the ciphertext was modified, decryption will fail.