Capillary is a library to simplify the sending of end-to-end encrypted push messages from Java-based application servers to Android clients. - google/capillary

Developers already use HTTPS to communicate with Firebase Cloud Messaging (FCM). The channel between FCM server endpoint and the device is encrypted with SSL over TCP. However, messages are not encrypted end-to-end (E2E) between the developer server and the user device unless developers take special measures.

To this end, we advise developers to use keys generated on the user device to encrypt push messages end-to-end. But implementing such E2E encryption has historically required significant technical knowledge and effort. That is why we are excited to announce the Capillary open source library which greatly simplifies the implementation of E2E-encryption for push messages between developer servers and users' Android devices.

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