we have a service who has a list of public keys got from clients (for example 1000 public keys. not too many)
service gets an encrypted message from one of clients. this message is encryped with a public key and defenitly service has that key.
can service find out which public key is used to encrype that data?
for more information (you can ignore it): service must broadcast data between all the clients (each one has a pair of RSA keys and service has their public keys). clients must send message to each other with no clue for tracking on service.
for example client A wants to send a message to client B. A encrypts the message with Bs public key and sends it to service. service broadcasts the message to all clients. but only one of the clients (it's B) can decrypt the message.