, ▁in ▁practice , ▁the ▁term ▁relativ istic ▁quantum ▁crypt ography ▁is ▁used ▁for ▁relativ istic ▁crypt ography ▁too . ▁ ▁History ▁In ▁ 1 9 9 7 ▁and ▁ 1 9 9 8 , ▁some ▁important ▁tasks ▁in ▁m istr ust ful ▁crypt ography ▁were ▁shown ▁to ▁be ▁impossible ▁to ▁achieve ▁with ▁un cond itional ▁security . ▁May ers ▁and ▁Lo ▁and ▁Ch au ▁showed ▁that ▁un condition ally ▁secure ▁quantum ▁bit ▁commit ment ▁was ▁impossible . ▁Lo ▁showed ▁that ▁ob liv ious ▁transfer ▁and ▁a ▁broad ▁class ▁of ▁secure ▁comput ations ▁were ▁also ▁impossible ▁to ▁achieve ▁with ▁un cond itional ▁security ▁in ▁quantum ▁crypt ography . ▁Moreover , ▁Lo ▁and ▁Ch au ▁showed ▁that ▁un condition ally ▁secure ▁ideal ▁quantum ▁coin ▁toss ing ▁was ▁impossible ▁too . ▁In ▁this ▁context , ▁Kent ▁provided ▁in ▁ 1 9 9 9 ▁the ▁first ▁relativ istic ▁crypt ographic ▁protocol s , ▁for ▁bit ▁commit ment ▁and ▁ideal ▁coin ▁toss ing , ▁which ▁overcome ▁the ▁assumptions ▁made ▁by ▁May ers , ▁Lo ▁and ▁Ch au , ▁and ▁achieve ▁un cond itional ▁security . ▁Since ▁then , ▁other ▁un condition ally ▁secure ▁relativ istic ▁protocol s ▁for ▁bit ▁commit ment ▁have ▁been ▁found ▁by ▁Kent ▁and ▁others , ▁and ▁other ▁crypt ographic ▁tasks ▁have ▁been ▁investig ated ▁in ▁the ▁setting ▁of ▁relativ istic ▁quantum ▁crypt ography . ▁ ▁Bas ics ▁ ▁No - sign alling ▁and ▁no - super l um inal ▁sign alling ▁The ▁no - sign alling ▁principle ▁of ▁quantum ▁theory ▁states ▁that ▁information