Fog of war refers to the unknown variables in a situation. It has its origins in 19th century warfare, where a general had to maintain knowledge of enemy positions and the status of friendly soldiers. If one of your scouts failed to return with updates from the battlefield, and you didn’t send reinforcements, you could get caught in a surprise attack. Knowing your opponent’s goals and orders ahead of time could save you resources.
Games have been used to simulate war since much earlier, in the 18th century. Players training against each other for the real thing would often get to hide their units until the match began; later additions used multiple boards to maintain fog of war throughout the game. To this day, common household board often let you hide your pieces by keeping them face down or towards you. Card games operate on the same principle.
Fog of war is also familiar to most video gamers. As you explore any game world, the map is typically uncovered in the process, but an area might change while you’re away. In strategy games, knowledge of the map is often crucial to victory over opponents; in games like Starcraft, players use scouts to monitor each other, and build defenses when the opponent builds units.
As a result, some players try to cheat. Older players remember the dreaded “screen looker,” that kid who would focus on your part of the TV and make it impossible to have a realistic game. This became impossible in Starcraft when players were at separate houses, so some would try to use hacking software. Data had to be handled with care to prevent hackers from accessing information that would give them an unfair advantage.
Blockchains are all about data, of course. Most of them are transparent, meaning everyone can see everything. Games such as Huntercoin which rely on such blockchains allow players to see the whole map, which prevents surprise attacks of any kind. You can even see their orders as their transactions pass through your node on the peer-to-peer network.
Of course, most blockchain games still use a central server. Games utilizing “token economics” risk revealing how much cryptocurrency a player has, while games utilizing “true ownership” may reveal their items. This might be desirable for bragging rights, but could be undesirable for the purposes of thwarting thieves and competitors.
A simple solution is to simply not reveal your public key and to make a new one for every game. This should suffice for most users. True lords of the dark web, however, could theoretically use blockchains such as Monero—which obfuscate where money is flowing to and from—to further hide their tracks.
Emerging solutions to allow traditional fog of war in fully decentralized online games have been developed by the XAYA team. In Xayaships, players send a signed timestamp of their chosen locations for their units. At the end of the game, they reveal their tiles, and can use the timestamps to verify each other’s honesty. Cheaters lose whatever they bet.
In another example, Daniel Kraft hypothesized in one paper for a scientific journal that blockchain sharding—where the blockchain is broken up into pieces, each of which are held by only a few players—could be used to scale massive multiplayer online games. Players would only need to see tiles on the map close to them, and would not be granted access to shards for hidden areas. Provable fairness ensures that players are not deceived this way.