New answers tagged protocol-design
You're confused about a few different things here. Assume that you have some cryptographic concept and you need to write down a definition of security. Such a definition can typically be written down as a game. When you write down your definition, you consider what the adversary should be able to do, i.e. it's while writing down the game that you assume ...
If you aren't worried about collusion or dynamic group membership, then a very simple solution is to simply have one key for encrypting the messages and another for signing them. The encryption key gives someone read access and the signing key gives them write access. Only nodes with the encryption key will be able to successfully decrypt the messages and ...
In distributed systems it is often bad practice to have "Shared Master Key". If a bad guy breaks in one of your devices he has the most important crypto piece of the system, and you're pretty much done. Rather have one key per device, and these keys are signed by an Authority I would say.
Some observations, though I would recommend against inventing your own protocol, at least for real world use: When a new Chat group is formed, a random AES Key is generated and encrypted using each users public key. This means the protocol lacks forward secrecy. Anyone who compromises the private key of a chat participant can decrypt any previous chats ...
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