Authentication in secure group messaging

Abstract

A receiver user device authenticates a received message in a group messaging protocol by receiving and storing a public token associated with a sender, receiving a private token and an encrypted message, and verifying the private token against the public token using a one-way function, such as a hash, wherein the public token is obtainable by hashing the private token. A server may forward the token and encrypted message to the receiver. The server may receive a message authentication code (MAC) from the sender, wherein the MAC is generated using a MAC key associated with the messaging group. The server may check the MAC using the MAC key and only make the message available to the group of users if the MAC matches the ciphertext. The one-way function may be SHA 256 truncated to sixteen bits. In another aspect, a messaging group uses a system key pair, a local key pair, and a tracer key pair to authenticate a message. The tracer keys are associated with the local group and are used to unlock the system signature of a message to verify that the sender is part of the local group.

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