Читать книгу Optical Cryptosystems - Naveen K. Nishchal - Страница 15

Asymmetric key cryptography is also known as public key cryptography. It refers to a cryptographic algorithm which requires two separate keys, one of which is private and another is public. The public key is used to encrypt the message and the private one is used to decrypt the message. This method was developed to address the key management issue of symmetric key cryptography. The process of asymmetric cryptography is shown in figure 1.4. It is a very advanced form of cryptography. Officially, it was invented by Whitfield Diffie and Martin Hellman in 1975. The basic technique of public key cryptography was first discovered in 1973 by the British Clifford Cocks of Communications-Electronics Security Group but this was a secret until 1997. The examples of symmetric key cryptography are discussed below [6].

 Digital signature standard (DSS): the DSS is a digital signature algorithm developed by the US National Security Agency to generate a digital signature for the authentication of electronic documents. DSS was put forth by the National Institute of Standards and Technology (NIST) in 1994.

 RSA: (Rivest, Shamir, and Adleman who first publicly described it in 1977) It is an algorithm for public-key cryptography. It is the first algorithm known to be suitable for signing as well as encryption, and one of the first great advances in public key cryptography. RSA is widely used in electronic commerce protocols, and is believed to be secure given sufficiently long keys and the use of up-to-date implementations.

 ElGamal: ElGamal is a public key method. It is used in both encryption and digital signing. The encryption algorithm is similar in nature to the Diffie–Hellman key agreement protocol and is used in many applications and uses discrete logarithms. ElGamal encryption is used in the free GNU Privacy Guard software.

Figure 1.4. Asymmetric key cryptography.