# What is AES-GCM encryption?

> AES-GCM is the encryption standard behind iMessage, iCloud and many security apps. What it does, why it matters for your photos, and how PureVault uses it.

URL: https://purevault.hoppedev.app/what-is-aes-gcm-encryption
Updated: 2026-10-20

You see 'AES-256' and 'AES-GCM' mentioned in security apps and privacy policies. Here is what those terms actually mean, in plain language, and why they matter when an app says it encrypts your photos.

## AES: the encryption standard

AES stands for Advanced Encryption Standard. It was standardized by NIST (the U.S. National Institute of Standards and Technology) in 2001 and is used worldwide to protect classified government data, banking transactions, and consumer software. AES-256 means the encryption key is 256 bits long — a number so large that trying every possible key would take longer than the age of the universe with current technology.

AES is a symmetric cipher: the same key encrypts and decrypts the data. That makes it fast and efficient on a phone. Apple uses AES hardware acceleration built into every iPhone's chip.

## GCM: authenticated encryption

GCM stands for Galois/Counter Mode. It is a specific way of using AES that provides two things at once: confidentiality (nobody can read the data without the key) and authenticity (if anyone tampers with the encrypted data, decryption fails instead of producing corrupted content). NIST published GCM as SP 800-38D.

This matters because encryption alone does not prevent someone from flipping bits in your encrypted file. With GCM, any modification is detected automatically. You either get the correct original data or an error — never silent corruption.

## Where you encounter AES-GCM

- **iMessage and FaceTime** use AES in various modes for end-to-end encryption.
- **iCloud with Advanced Data Protection** encrypts your data end-to-end on Apple's servers.
- **HTTPS/TLS** — the lock icon in your browser — often negotiates AES-GCM for the session.
- **iPhone Data Protection** uses AES to encrypt files on your device, with keys tied to the Secure Enclave and your passcode.

## How PureVault uses it

[PureVault](https://purevault.hoppedev.app/) encrypts every vault item — photos, videos, PDFs, notes — with AES-GCM on your device. The encryption key is generated locally and stored in the iPhone's Keychain, protected by the Secure Enclave. No key is sent to a server. When you open a vault item, PureVault decrypts it locally; if the data has been altered, GCM's authentication tag catches it.

[Get it on the App Store](https://apps.apple.com/us/app/purevault-private-photo-vault/id6760844803)