D.net will make it public. Taken from d.net faq:
'What happens when the key is found?
When a client finds a key that correctly deciphers the first few bytes of the message (the first part of the message is known to be the text "The unknown message is:"😉 it sends an alert back to the Bovine organizers. Using separate software we attempt to decrypt the entire message. If successful RSA is notified. After RSA verifies that the correct key has indeed been found press releases are issued by us and RSA and the check for the prize amount ($10,000 U.S.) is mailed to Bovine. Bovine then distributes the money as described earlier.
How will I know if my computer found the key?
Initially you won't. We've set the clients up intentionally so as not to alert the user if a candidate key is found. There are several reasons for this. First, we have gone to a lot of effort to make this project successful. We want to make sure that we maintain control over the winning key until RSA has been notified. Secondly, a lot of people running the clients don't want the client playing Yankee Doodle Dandy if it finds the key. They run the clients in their office, on there secretary's machines, etc. and aren't looking for a lot of attention. Finally, the clients only perform a partial message decryption and it is possible (although unlikely) for them to generate false positives. There is no need to get excited until the key has been verified.'