github.com/oxzi/xochimilco (go): Package xochimilco provides an usable API for end-to-end encrypted communication based on the "Signal Protocol".  The "Signal Protocol" refers to the Extended Triple Diffie-Hellman (X3DH) key agreement protocol paired with the Double Ratchet algorithm. Both are implemented and exposed in this repository's subdirectories. For implementation details please refer there.
Keywords: double-ratchet|signal-protocol|x3dh