In a one-time pad, if a messagemof length`is is encrypted with a keyk= 0`(i. e.,kconsists of all 0s) thenenck(m) =m. That is why, it issometimes suggested to prohibit this key. In other words, the keyspace isrestricted to strings which are all not zeros. Is the resulting cryptosystemperfectly secure?

the major difference between the two is the objective and the reward of the game. candy crush has a puzzle theme with the objective of meeting a specific quota of points or objects, you are able to gain access to the next level and compete with peers on the process. on duolingo the objective is rather different, you are given sets of questions for you to answer for you to move to the next level and as for the reward, you are able to learn available language as this is an app developed to teach the user about other languages.