Broadcast encryption not using symmetric keys Is there a common scheme for broadcast encryption that doesn't involve an exchange of a shared key? I'm aware that traditionally a common symmetrical key would be given to all parties and exchanged securely using the recipients' public keys.
I'm building an application on the Ethereum blockchain where I want to use one message to transmit information to all recipients involved securely. Unfortunately, this means revoking keys becomes an expensive process due to Ethereum transaction costs, as I would have to redistribute a new symmetric key to all recipients again.
Is there any way to encrypt a message using a set of public keys that could be decrypted by any of their respective private keys so that revocation is not so expensive? I would not include the revoked public key the next time I send an update. The message is quite a small amount of text, so size should also not be a problem.
Asynchronous Ratcheting Tree (ART) is an n-way Diffie-Hellman key exchange. The group initiator selects members and instantiates the tree, revealing only public information such that each other member may recompute the group shared key. Users may update their key-share as a measure to implement forward secrecy of a later compromise of their long-term static identity key.

As you're interested in at least revocation, you'll want to extend ART with dynamic groups which introduce the operations: join, leave, partition and merge.

Leaving is done willingly, however, partitioning and merging can enable selective revocation, computing partial tree updates without recomputing a whole new tree (which is not too expensive anyway).

With the group key you now use symmetric authenticated encryption.

Edit: You may additionally use the group key to derive a shared asymmetric identity such that anyone may encrypt messages to the group; but only group members (1-of-n) may decrypt the messages. As the group membership changes, the encrypting user is responsible for using the latest identity to encrypt for.