1 Should Chess Players Learn Computer Security? Gildas Avoine, Cedric´ Lauradoux, Rolando Trujillo-Rasua F Abstract—The main concern of chess referees is to prevent are indeed playing against each other, instead of players from biasing the outcome of the game by either collud- playing against a little girl as one’s would expect. ing or receiving external advice. Preventing third parties from Conway’s work on the chess grandmaster prob- interfering in a game is challenging given that communication lem was pursued and extended to authentication technologies are steadily improved and miniaturized. Chess protocols by Desmedt, Goutier and Bengio [3] in or- actually faces similar threats to those already encountered in der to break the Feige-Fiat-Shamir protocol [4]. The computer security. We describe chess frauds and link them to their analogues in the digital world. Based on these transpo- attack was called mafia fraud, as a reference to the sitions, we advocate for a set of countermeasures to enforce famous Shamir’s claim: “I can go to a mafia-owned fairness in chess. store a million times and they will not be able to misrepresent themselves as me.” Desmedt et al. Index Terms—Security, Chess, Fraud. proved that Shamir was wrong via a simple appli- cation of Conway’s chess grandmaster problem to authentication protocols. Since then, this attack has 1 INTRODUCTION been used in various domains such as contactless Chess still fascinates generations of computer sci- credit cards, electronic passports, vehicle keyless entists. Many great researchers such as John von remote systems, and wireless sensor networks. Neumann, Claude Shannon, and Alan Turing to The origin of this article comes from recent news name a few have spent time studying chess pro- about cheating in top-level chess tournaments. A gramming. John Conway was also attracted by the famous case is the Georgian chess champion and game of chess and, in general, by combinatorial grandmaster Gaioz Nigalidze who was caught in game theory. He introduced a popular chess fraud April 2015. He used a smartphone with a head- known as the chess grandmaster problem, where a set in the restroom during the Dubai Open Chess little girl Anne-Louise, who has never heard of Tournament. He was banned for three years and his chess, wants to face two grandmasters, Bobby Fis- grandmaster title was revoked. cher and Boris Spassky, in correspondence chess. In 2010, several French grandmasters, including Has she lost her mind? Not really, she has a clever the coach of the national team cheated during the strategy which consists in playing Black against chess Olympiad at Khanty-Mansiysk. The grand- Fischer and White against Spassky. Once Fischer master Sebastien´ Feller was helped by his fellows sends his first move, Anne-Louise copies this move Arnaud Hauchard and Cyril Marzolo to win his and sends it to Spassky. Then, she waits Spassky’s games by using a combination of cell phones, com- move and forwards it to Fischer. And so on, until puter, and body language to inform the grandmas- she either wins one of the games or draws both of ter of the best moves to play. them. Anne-Louise only relays the moves between In the same year, Veselin Topalov accused the two grandmasters. So the two grandmasters Vlad´ımir Kramnik´ of cheating during their match for the world chess title at Elista. Topalov’s accusa- G. Avoine is a member of INSA Rennes, IRISA, and the Institut tions against Kramnik´ were motivated by his oppo- Universitaire de France. nent’s suspicious behavior: he visited the restroom C, Lauradoux is a member of Inria Rhˆone-Alpes R. Trujillo-Rasua is with the University of Luxembourg and the with an unusual frequency. Topalov’s supporters Interdisciplinary center of Security, Reliability, and Trust. claimed that Kramnik´ received help in the restroom. 2 An interesting cheating allegation occured at the the earliest documented use of a covert channel can 2006 World Open in Philadelphia. After an impres- be found in the Greek book Histories by Herodotus sive streak of wins, an unknown player was caught written in 440 BC; a slave was used to secretly bearing several electronic devices including a cover transmit a message by shaving the slave’s head, earring device. He was accused of getting help from tattooing the message, letting the hair growing, and an accomplice. sending the slave to the intended recipient who has Certainly, chess fraud has a long history and to shave the slave’s head again in order to retrieve did not wait for the new technologies to be imple- the message. mented. All a cheating player needs is to be aided Practically, any ordinary thing can be used as a by a stronger chess player. The challenge is that covert channel. In chess, players who are used to nowadays we all have access to the strongest chess play with pieces they have taken during a game, player ever: the computer. The question therefore is can use this apparently inoffensive behaviour to whether the next world chess champion will be a exchange information with somebody else. human player or a computer. We put our two cents The use of covert channels in chess is actually in this question by analyzing chess fraud from a nicely illustrated through the famous cheating scan- computer security perspective. dal during the 2010 FIDE Olympiad Tournament at Khanty-Mansiysk, where the French coach used 2 OVER-THE-BOARD CHESS movement patterns within the playing venue to communicate with his team. The fraud works as When computers started to be stronger than grand- follows. The coach stops in front of a given chess- masters, some players have seized this opportunity board. If he is by the side of the black or of the white, to cheat. Instead of using their brain on the board, the player understands a different coordinate. The they use it to elaborate strategies to receive com- coach and the player agree on 64 positions in the puter advices during their games. This is strictly playing area before the tournament. The move rep- forbidden by the rules of chess, but dishonest play- resentation associated to the coach position is the ers have been extremely cunning and have devel- long algebraic chess notation: the rows of the board oped different types of covert channels to transmit are identified by a number and the columns by a information without being caught. This section ad- letter. The symbol (letter, number)-(letter, number) dresses this fraud by considering the game of chess indicates the starting square and the destination in its simplest form, that is, in a face-to-face battle. square (see Figure 1). Such a scheme requires twelve We assume that chess games are setted up in bits to communicate a move. The French grand- such a way that the players are convinced of the masters used an inefficient board representation. identity of their opponents. This can be achieved Indeed, by using standard techniques in computer by face recognition, identity document verifica- sciences a chess move can be encoded with less bits, tion, or any other biometrics authentication mech- implying that this type of chess fraud can be quite anism. Thus, cheating strategies such as allowing a hard to prevent. twin brother or sister to play on one’s behalf are To illustrate this, we remark that the com- out of our scope. We do not cover either uneth- pact communication of a chess move is fully an- ical behaviours such as rate manipulation, inten- swered by Shannon’s works on communications tional draws, kicking/insulting a player, or touch- and chess [11]. Entropy or uncertainty is for the ing pieces. The chess fraud we focus on consists in chess player the branching number of the position, the use of external help during a game. Whether i.e., the number of legal moves he can make on the such help is useful to perform better or not is re- board and denoted b . The player and the accom- garded irrelevant; in the same way that many drugs p plice needs to agree on a method to enumerate all in sport competitions are banned even though they the moves, for instance from left (a) to right (h) and do not enhance performance. Given that referees top (8) to bottom (1). So, the accomplice needs to (if any) are considered to be honest, it follows that communicate dlog (b )e bits to the player. Note that any communication channel between a player and 2 p there is no ambiguity with such a coding system: a third party must go through a covert channel. two pieces can reach the same square but these two different moves have different numbers. Shannon 2.1 Covert channels estimated that the maximum number of available A covert channel is a communication channel that moves in a given position is max(bp) ≈ 35. Conse- was not intended for information transfer. One of quently, only six bits instead of twelve are needed in 3 8 the system, detect the attack, react to the attack, rmblkans and mitigate the damage. FIDE already has a 7 opo0Zpop comprehensive set of rules to react to chess fraud and mitigate their impact. Ergo we focus next on 6 0Z0ZpZ0Z protection and detection. 5 Z0ZpZ0Z0 Discarding Any Channel. A fundamental counter- 4 0Z0OPZ0Z measure in computer security to prevent the use 3 Z0Z0Z0Z0 of covert channels consists in isolating the system. For example, tempest shielded rooms are commonly 2 POPZ0OPO used in sensitive areas to circumvent covert chan- 1 SNAQJBMR nels [9]. Isolation is also used in smartcards to make a b c d e f g h them tamper-resistant.