Asymmetric Public‐Key Cryptosystems

Public-key cryptography became public soon after Whitefield Diffie and Martin Hellman (1976) proposed the innovative concept of an exponential key exchange scheme. Only a few public-key algorithms are both secure and practical. Of these, only some are suitable for encryption. Others are only suitable for digital signatures. Among these numerous public-key cryptography algorithms, only four algorithms, RSA (1978), ElGamal (1985), Schnorr (1990), and elliptic curve cryptosystem (ECC) (1985), are considered to be suitable for both encryption and digital signatures. Another public-key algorithm that is designed to only be suitable for secure digital signatures is Digital Signature Algorithm (DSA). The designer should bear in mind that the security of any encryption scheme depends on the length of the key and the computational work involved in breaking a cipher.