Bit of an old question, How do cd keys work

[thegussbus123]

Back in the day, when purchasing a retail disc for games a key code would come with it. My question is how do makes control the use of the game especially if its an offline game (single payer) if people just rent it to a friend. Do the makers know if you simply use it offline. Or is the set of codes the same for all copies?

 

[USAFRet]

Back in the day, when purchasing a retail disc for games a key code would come with it. My question is how do makes control the use of the game especially if its an offline game (single payer) if people just rent it to a friend. Do the makers know if you simply use it offline. Or is the set of codes the same for all copies?

Older games would make you look up certain info on a certain page in the user manual.
Presumably you and your friend do not have 2 copies of the user manual.

Later, with a "license key"...the letters and numbers in the license key would result, through some algorithm in the game code, to end up at a certain answer.

For instance, of the key were "1234", somewhere in the game code would be the answer "10" (1+2+3+4=10)
Any combination of other numbers would result in an answer other than "10", and be rejected.
Obviously more complex than that, but that is the general idea.

Later, the game would phone home once.
"This game is now registered to "gussbus" "
Another registration attempt would fail.

Later, they would require talking to the game server once in a while.

Today...they talk to the game server all the time.