Complex sentence: The public key is a'hard' knapsack, and the private key is an'easy', or superincreasing, knapsack, combined with two additional numbers, a multiplier and a modulus, which were used to convert the superincreasing knapsack into the hard knapsack.
Split into simpler sentences: The public key is a'hard' knapsack, and the private key is an'easy', or superincreasing, knapsack, combined with two additional numbers, a multiplier and a modulus. The multiplier and modulus can be used to convert the superincreasing knapsack into the hard knapsack.