End-to-end encryption in chats

What is encrypted

Text, reactions, edits, photos, files, voice messages, locations and contact cards. Each is encrypted on your phone with the Signal Protocol for every phone of the person you are writing to, and for your own other devices. The server stores and delivers the encrypted copies and cannot read them. Each copy is deleted from the server once the phone it was made for has it, or after 30 days.

Photos, files and voice messages are encrypted on the phone with their own key before upload. Storage holds only the encrypted file; the key travels inside the encrypted message.

Group chats

A group is protected the same way as a one-to-one chat. When someone joins or leaves, the keys change. The server stores the group’s name, picture and member list, which it needs to run the group.

Checking who you are talking to

Each chat has a safety number. Compare it with the other person, in person or by scanning a code; if it matches, nobody is in between.

The keys for a new chat come from AiThao’s server. If the other person has not finished setting up their phone, there are no keys to encrypt for, and the app sends nothing rather than falling back to an unencrypted message.

On your phone

Your conversation history on the iPhone is protected by iOS Data Protection and excluded from iCloud and computer backups. AiThao has its own encrypted backup instead, described under “Your data”. You can also require Face ID or your passcode to open the app.

Where the protection ends

• Translation: to translate a message, your phone decrypts it and sends the text to a cloud translation service.
• Older conversations: a chat that began before end-to-end encryption keeps its earlier messages on the server as they were.
• Metadata: who wrote to whom and when, message size and delivery state are visible to the server.