Different from traditional symmetric cryptography,public key cryptography allows each user to own a pair of public/private key pair.Given the public key of one user and the data to be encrypted,a ciphertext can be generated such that only the intended user is able to recover the data using his/her private key associated with public key involved in the encryption process.To really understand the philosophy behind the public key cryptography is not an easy task and sometimes it seems somewhat difficult,if not impossible,for the beginners without the knowledge of the abstract algebra and number theory.In this paper,we introduce briefly the basic definition of public key cryptography as well as the corresponding mathematical hard problems.Besides,we explain why the mathematical backgrounds,especially abstract algebra and number theory,matter in the study of public key cryptography.