▁was ▁secure . ▁ ▁Information - the oret ically ▁secure ▁crypt os ystem s ▁have ▁been ▁used ▁for ▁the ▁most ▁sensitive ▁government al ▁communic ations , ▁such ▁as ▁diplom atic ▁c ables ▁and ▁high - level ▁military ▁communic ations , ▁because ▁of ▁the ▁great ▁efforts ▁enemy ▁govern ments ▁exp end ▁toward ▁breaking ▁them . ▁ ▁There ▁are ▁a ▁variety ▁of ▁crypt ographic ▁tasks ▁for ▁which ▁information - the or etic ▁security ▁is ▁a ▁meaning ful ▁and ▁useful ▁requirement . ▁A ▁few ▁of ▁these ▁are : ▁ ▁Secret ▁sharing ▁schemes ▁such ▁as ▁Sh am ir ' s ▁are ▁information - the oret ically ▁secure ▁( and ▁also ▁perfectly ▁secure ) ▁in ▁that ▁having ▁less ▁than ▁the ▁requ is ite ▁number ▁of ▁shares ▁of ▁the ▁secret ▁provides ▁no ▁information ▁about ▁the ▁secret . ▁ ▁More ▁generally , ▁secure ▁multip art y ▁computation ▁protocol s ▁often ▁have ▁information - the or etic ▁security . ▁ ▁Private ▁information ▁retr ieval ▁with ▁multiple ▁databases ▁can ▁be ▁achieved ▁with ▁information - the or etic ▁priv acy ▁for ▁the ▁user ' s ▁query . ▁ ▁Red u ctions ▁between ▁crypt ographic ▁primit ives ▁or ▁tasks ▁can ▁often ▁be ▁achieved ▁information - the oret ically . ▁Such ▁redu ctions ▁are ▁important ▁from ▁a ▁theoretical ▁perspective ▁because ▁they ▁establish ▁that ▁primitive ▁ ▁can ▁be ▁realized ▁if ▁primitive ▁ ▁can ▁be ▁realized . ▁ ▁Sym metric ▁encryption ▁can ▁be ▁constructed ▁under ▁an ▁information - the or etic ▁notion ▁of ▁security ▁called ▁ent rop ic ▁security , ▁which ▁assumes ▁that ▁the ▁advers ary ▁knows