▁can ▁be ▁two ▁companies ▁with ▁offices ▁and ▁labor ator ies ▁at ▁various ▁locations ▁in ▁the ▁Earth . ▁Alice ’ s ▁offices ▁and ▁labor ator ies ▁work ▁in ▁collaboration ▁and ▁trust ▁each ▁other . ▁Similarly , ▁Bob ’ s ▁offices ▁and ▁labor ator ies ▁work ▁in ▁collaboration ▁and ▁trust ▁each ▁other . ▁But ▁Alice ▁and ▁Bob ▁do ▁not ▁trust ▁each ▁other . ▁ ▁Task s ▁investig ated ▁in ▁relativ istic ▁crypt ography ▁ ▁Bit ▁commit ment ▁ ▁Bit ▁commit ment ▁is ▁an ▁important ▁crypt ographic ▁task ▁that ▁has ▁been ▁widely ▁investig ated ▁in ▁relativ istic ▁crypt ography . ▁In ▁bit ▁commit ment , ▁Alice ▁commits ▁to ▁a ▁bit ▁b ▁at ▁some ▁time ▁t , ▁and ▁at ▁some ▁later ▁time ▁t ’ ▁> ▁t ▁Alice ▁un ve ils ▁her ▁committed ▁bit ▁b ▁to ▁Bob . ▁A ▁bit ▁commit ment ▁is ▁said ▁to ▁be ▁" h iding " ▁if ▁Bob ▁cannot ▁know ▁b ▁before ▁Alice ▁un ve ils . ▁It ▁is ▁said ▁to ▁be ▁" binding " ▁if ▁after ▁the ▁commit ment ▁time ▁t , ▁Alice ▁cannot ▁choose ▁the ▁value ▁of ▁b ▁and ▁successfully ▁un ve il ▁b ▁to ▁Bob . ▁A ▁bit ▁commit ment ▁protocol ▁is ▁" secure " ▁if ▁it ▁is ▁hiding ▁and ▁binding . ▁The ▁May ers - Lo - Ch au ▁no ▁go ▁theorem ▁states ▁that ▁un condition ally ▁secure ▁bit ▁commit ment ▁is ▁impossible ▁based ▁only ▁on ▁the ▁laws ▁of ▁quantum ▁physics . ▁It ▁was ▁shown ▁by ▁Kent ▁that ▁the ▁May ers - Lo - Ch au ▁theorem ▁is ▁not ▁general