Glacier users uses a Double Ratchet algorithm to establish secure sessions between every combination of devices for you and your contact(s). The Double Ratchet Algorithm uses Curve25519, AES-256, and HMAC-SHA256. Those sessions are then being used to communicate secure keys to all devices. Glacier will generate a new key for every message. That key is used to encrypt your message with AES-GCM.
The security of these algorithms has been tested over many years of use, in hundreds of different applications. Our messages and calls are end-to-end encrypted, which means that they can only be read or heard by your intended recipients. Glacier does not have access to the contents of any messages or calls sent or received by our users.