Is cloud photo backup encrypted, and who holds the key?

When a service says your photos are “encrypted”, it is telling the truth and leaving something out. The detail that matters is who holds the key.

Three kinds of encryption

1. In transit

Your photos are scrambled while they travel between your phone and the server, so nobody on the network can read them. This is standard everywhere. It protects the journey and nothing else.

2. At rest, with the provider’s key

The server stores your photos in scrambled form. If someone stole a disk from the data center, they couldn’t read it. But the provider holds the key, so the provider’s systems can unscramble your photos whenever they need to.

iCloud’s own security overview describes exactly this for standard settings: the provider keeps the keys in its data centers so it can decrypt your data on your behalf, for example when you sign in on a new device or restore a backup. That is also why it can help if you forget your password. Google Drive’s help pages say files are encrypted in transit and at rest, and describe an optional client-side encryption feature, available through a Workspace administrator, as the one where the provider can’t decrypt your files. That tells you what ordinary accounts get: the provider holds the keys.

This is the default for most cloud photo backup, including your gallery app’s backup.

3. End-to-end

Your devices hold the key, and the provider never has it. The provider stores scrambled data it can’t open, even if it is breached or ordered to hand it over. That is the strongest option, and the cost is that nobody can recover your data for you.

What the major services offer

iCloud. Standard protection is type 2. Photos and backups are encrypted in transit and on the server, with provider-held keys. Some categories, such as saved passwords and health data, are end-to-end encrypted by default. iCloud also has an optional end-to-end encryption setting that extends end-to-end encryption to most of your data, including photos and device backups. The help page lists the conditions:

• You must set up a recovery method first, such as a recovery contact or a recovery key. The provider can’t help you recover otherwise.
• Every device you sign in on has to run a recent enough software version.
• Access on the web is turned off while it is on.
• Shared albums and links to “anyone with the link” aren’t end-to-end encrypted, even with the setting on.

You turn it on in Settings, under your name, then iCloud.

Google Drive. Files are encrypted in transit and at rest. End-to-end style client-side encryption is not something a normal account can switch on.

Your gallery app’s backup. Ask the same question: who holds the key? Look for the word end-to-end in the app’s help. If you can’t find it, assume the provider can read your photos.

Why it matters

• Breaches and requests. If the provider holds the key, your photos can be exposed by a breach of the provider or handed over under legal demand.
• Staff and scanning. Provider-held keys make it possible for the provider to process your files, for example to scan them.
• Recovery. Provider-held keys mean account recovery works. Keys only you hold mean it doesn’t.

None of this means cloud backup is a bad idea. It means that the type of encryption decides how private the backup is.

The do-it-yourself fix

You can get end-to-end protection on any cloud by encrypting before upload. The app on your phone scrambles the files with a key derived from your own secret, then sends them. The cloud, whichever you use, sees only noise. Silo’s backup works this way. It is arriving with launch, and it is a Pro feature. It encrypts on your phone and then uploads to your own cloud storage account, Google Drive on Android first and iCloud on iPhone later. Silo’s developer has no access to it. Your recovery phrase is what restores it, so keep it safe: see what is a recovery phrase. Silo is coming soon.

If you are moving to a new phone, move your vault to a new phone covers how backup fits in.