Suppose that there is a sender of a message that is broadcasted, where the receivers of the message would need to be sure that the message is really coming from that sender and not from somebody else.
Are there encryption algorithms that allow this, assuming that only unidirectional (from sender to receiver) communication is possible?
With symmetric encryption, the receivers normally can also encrypt so any receiver with a key could pretend to be the sender. With asymmetric encryption, I understand from this and this questions that it is (usually) trivial to find the public key based when you have the private key, so again a receiver who has the private key could pretend to be a sender. However, in those questions, I seem to understand from some of the answers that this should be possible. What algorithms would allow this?
If I search for this, I came across identity-based encryption, but it seems that it requires bi-directional communication with, in this case, a trusted third party, which would not be possible in my use case (receivers are only able to receive communication, not send anything themselves).