Paradigm shift from classical cryptography to quantum cryptography

Cryptography is the technique of masking the message by means of any encryption method so that intended entity can decrypt the contents. Cryptanalysis is the art of retrieving plain text from cipher text with no prior information about technique or key used for encrypting the message. An intruder can attack in many ways to access the communication channel like impersonating, non-repudiation, denial of services, modification of data, threatening confidentiality and breaking availability of services. Thus, the security of any cryptographic schemes lies on the strength of particular hard problem like the integer factorization problem, the discrete logarithm problem in the multiplicative subgroup and on an elliptic curve. Nonetheless, with increased speed and memory of computers and stronger cryptanalytic algorithms, the two problems discrete logarithm problem in the multiplicative subgroup and the integer factorization problem, earlier considered to be strong and hard can be cracked in sub exponential time. Elliptic curve DLP has advantages over the other two: it generates shorter keys and is still an exponentially hard problem for classical and traditional computers. The circumstances will change if stronger attacks are discovered or fast computers are invented. Hence, researchers are predicting, quantum computers could solve Elliptic Curve Discrete Logarithm Problem in polynomial time. Researchers are working in the area to identify hard problems for quantum computers. Thus, the focus of the papers is on various available classical and quantum cryptographic schemes and its hardness with respect to classical and quantum computers respectively.