An Extended Knapsack Public Key Cryptosystem

We analyzed a typical cryptosystem and an easy extended knapsack subset sum problem is proposed. The solution is not chosen from any longer but from. Based on the problem, we construct a public key cryptosystem in which the plaintext is divided into some groups and each group has bits, so that the encryption and decryption can be very fast. The possible attacks are analyzed. Our cryptosystem not only can resist Shamir's attack but also can resist the low density attack, because of its high density. The number of the sequence is also much shorter than before with the same density.