SOURCE_URL: https://majikah.solutions/products/majik-message/docs/wiki-aes-256-gcm

---
title: "AES-256-GCM"
id: "wiki-aes-256-gcm"
group: "majik-message"
type: "products"
version: "1.1.0"
lastUpdated: "2026-02-19T00:00:00.000Z"
difficulty: "Beginner"
time: "3-4 minutes"
tags: [aes, aes-256, aes-256-gcm, symmetric-encryption, authenticated-encryption, gcm, cryptography]
---

# AES-256-GCM

> The symmetric cipher that encrypts your actual message content — providing both confidentiality and built-in tamper detection

## Overview
AES-256-GCM is the algorithm that encrypts the content of every message in Majik Message. While ML-KEM-768 handles securely sharing the encryption key between sender and recipient, AES-256-GCM is what actually scrambles the message so no one else can read it — and it includes a built-in mechanism to detect if the ciphertext has been tampered with.

### What is AES-256-GCM?

AES stands for Advanced Encryption Standard. It is the symmetric cipher used by the US government, banks, healthcare systems, and virtually all secure software worldwide. The 256 refers to the key length — 256 bits — providing the highest standard security level. GCM stands for Galois/Counter Mode, which is the mode of operation that adds two critical properties to basic AES: it produces a unique encrypted output for every message (via a random initialization vector), and it generates an authentication tag that detects any tampering with the ciphertext.

### AES-256-GCM vs. ML-KEM-768: What's the Difference?

These two algorithms serve different roles and work together. ML-KEM-768 is an asymmetric (public-key) algorithm — it uses a public key to encrypt and a private key to decrypt. It is used to securely deliver the encryption key to the recipient. AES-256-GCM is a symmetric algorithm — both encryption and decryption use the same secret key. It is fast, efficient, and used to encrypt the actual message content. The hybrid approach works like this: ML-KEM-768 securely delivers a shared secret to the recipient; that shared secret becomes the AES-256-GCM key; AES-256-GCM encrypts the message. Neither algorithm alone is sufficient — together they provide both quantum resistance and high-performance encryption.

### GCM Mode: Encryption Plus Integrity

A critical feature of GCM mode is authenticated encryption. In addition to encrypting the message, AES-256-GCM produces a 16-byte authentication tag — a mathematical fingerprint of the ciphertext. When you decrypt a message, the authentication tag is verified before decryption. If the ciphertext has been altered in any way — even a single bit — the authentication tag fails verification and decryption is rejected. This means AES-256-GCM protects against both eavesdropping (confidentiality) and tampering (integrity). This is why you cannot silently corrupt an encrypted message — any modification is immediately detected.

### Initialization Vector (IV): Why Every Encryption is Unique

AES-256-GCM uses a random 12-byte initialization vector (IV) for every message. Even if you encrypt the same plaintext twice with the same key, the IV ensures the resulting ciphertexts are completely different. This prevents pattern analysis attacks where an attacker might try to infer message content by comparing ciphertexts. The IV is not secret — it is stored alongside the ciphertext in the MJKB envelope and is required for decryption.

> **NOTE:** Is AES-256 Quantum-Safe? AES-256 is considered quantum-resistant for the foreseeable future. Grover's Algorithm — the quantum attack relevant to symmetric ciphers — effectively halves the key length, reducing AES-256 to approximately AES-128 equivalent security against a quantum attacker. AES-128 is still considered computationally infeasible to break. This is why Majik Message uses AES-256 specifically — the additional headroom accounts for quantum threats.