Capture the flag (CTF) is a traditional outdoor sport often played by children or sometimes adults where two teams each have a flag (or other marker) and the objective is to capture the other team's flag, located at the team's "base", and bring it safely back to their own base. Enemy players can be "tagged" by players in their home territory; these players are then, depending on the agreed rules, out of the game, members of the opposite team, or "in jail". (One variation of the game includes a "jail" area in addition to the flag on each team's territory.)
In this version, if a member of one team gets tagged by a member of the second team in the second team's territory, the tagged person must sit in jail either for a pre-determined time limit, or until an untagged member runs through the jail, often requiring tagging a member of his team in jail. When that team member is freed from jail he is allowed to return back to his territory without getting tagged. However, the team member who freed him is not safe, therefore they can retreive the flag and/or run back to their side. Because of this it is a good idea to determine that while on the opposing teams' side (excluding jail) an opposing team member can go wherever they like and do whatever they want (get the flag, free a team member, run around the territory, a combination, or nothing). However, it is in illegal move to put a flag in another place, create obstacles, or run out of bounds in hopes of not getting tagged. Also, when playing with many people it is possible to blend in with the opposing team and pretend to be in jail (without getting tagged) there, that team member may free team members who come into the jail - without getting noticed. In some cases, particularly if the jail is far from the boundary line between territories, players may be allowed to form a "human chain" from the jail towards the boundary. This makes it easier to be "rescued", the more players are in jail. The purpose of this rule may be to reduce the possibility of games ending in a virtual stalemate: if one team has nearly all its players in jail, allowing the opposing team to focus exclusively on the remaining members, it can prevent them from effecting either the release of prisoners or the capture of the flag. With this variation, with mutual consent from both teams, "Jail Break!" may be called, and all players in jail have a chance to run to their respective sides to freedom.
A common gameplay mode called "Capture the Flag" is found in many first-person shooters such as Team Fortress 2, Quake, Urban Terror, Unreal Tournament, Tribes, the Halo series, the Call of Duty series, the TimeSplitters series (renamed "Capture The Bag"), and Metroid Prime Hunters. CTF is even in some sports games like the Tony Hawk Pro Skater series. Each team has a flag and the players attempt to take the enemy's flag from their base and bring it back to their own flag to score. CTF is most commonly played in multiplayer games.
Possibly the first first-person shooter to feature CTF was Rise of the Triad, released in 1994, while the first real-time strategy to feature CTF was Command & Conquer in 1995. One of the multiplayer modes was called Capture the Triad, and conforms to the objectives stated above for CTF games in first person shooters, with the exception that the items to be captured/defended were triad symbols. Note that in FPSes, unlike the children's game, players can be harmed irrespective of whether they are in their own base.
CTF was popularized when it was first introduced as a modification to Quake by the company Threewave. CTF is also a popular mode in the Team Fortress and Team Fortress Classic mods for Quake and Half-Life respectively.
CTF mods are available for multiple first person shooters, including Wolfenstein: Enemy Territory, which is a free download using the game engine from the popular Return to Castle Wolfenstein.
Compared to a deathmatch game, CTF scenarios often feature some sort of transportation tool that can be used to travel faster and to reach areas which the player wouldn't normally be able to reach without this extra aid. Such tools might be a grappling hook or a portable teleporter. In Battlefield 1942 CTF the many vehicles available in the game serve this role, though in ETF the vehicles move slower than the players, and are vulnerable objectives in most missions. The usual reason for including such equipment is because it allows players to outmaneuver the flag carrier on his way home, as the flag carrier is often not able to use transportation tools. In Unreal Tournament 2004, for example, only players in ground vehicles can hold and thus capture the flag, whereas using air vehicles or the Translocator (a personal teleporter) will cause the player to drop the flag. The Halo series takes this concept a step further, preventing the flag carrier from not only driving a vehicle or boarding a vehicle as a passenger, but using weapons as well, unless the flag carrier willfully drops the flag. This feature gives the defenders an edge, thus making the game sessions last a bit longer. Unreal Tournament III introduces a Vehicle CTF mode, differentiated from normal CTF maps by the presence of vehicles and the replacement of the Translocator with a Hoverboard.
In the MMORPG Silkroad Online, players can play capture the flag free every 2 hours in the game. It is the same as capture the flag except the players attack the other players on the opposing team with their obtained skills. Also, to get the flag, players must kill monsters on their side of the field until they obtain a key that one of the monsters is holding.
In the MMORPG Runescape, paying members can play a mini-game called Castle Wars, which includes the basic principles of capture the flag. In another MMORPG, World of Warcraft, the Warsong Gulch battleground implements CTF-style gameplay.
There are also CTF variants for more than 2 teams (4 teams most commonly). In that case, the scoring system can vary greatly.
Contests are generally executed in a hotel ballroom or meeting room. A typical contest will have an area for each team playing, arranged around a central area reserved for the contest administrators. Projectors will display a scoreboard on the wall, which will be intermittently interrupted by witty or humorous video clips. Music is usually provided by a PA system during the contest.
CTF contests are usually designed to serve as an educational exercise to give participants experience in securing a machine, as well as conducting and reacting to the sort of attacks found in the real world. Reverse-engineering, network sniffing, protocol analysis, system administration, programming, and cryptanalysis are all skills which have been required by prior CTF contests at DEF CON.
CTF games often touch on many other aspects of information security, such as physical security, regulatory compliance, and software licensing. Successful teams generally have extensive industry experience and are capable of addressing these issues, even when raised by surprise in the middle of the contest.
An international, academic CTF was created by University of California, Santa Barbara in 2004. There have been 5 iCTF exercises since then. The 2007 edition occurred on December 7th, 2007 and involved 35 teams from across the world.