A system described herein may provide for secure group messaging between multiple participant devices, in which two or more of the participant devices support blockchain-based techniques for the secure sharing of keys used to secure the group messaging, and in which one or more of the participant devices (e.g., a third device) do not support such techniques. A key escrow system may maintain keys associated with the third device, and the other devices of the group messaging system may retrieve such keys from the key escrow system. Such other devices may attempt to obtain keys associated with the third device from a blockchain and may retrieve such keys from the key escrow system when the retrieval from the blockchain is unsuccessful. The other devices may additionally share their respective keys to the blockchain and the key escrow system, or the key escrow system may “pull” such keys from the blockchain.