Avoiding Key Escrow
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Figure 1.1 Symmetric-key cryptography where a single key is adopted for encryption and decryption.
1.2 SETTING OF ASYMMETRIC PKC In 1976, the notion of PKC was initially introduced by Diffie and Hellman  to eliminate the need for secure key distribution channels and supply the counterpart of a handwritten signature in the electronic world . The distinguishing feature of PKC is due to the fact that the key used to encrypt a message is different from the key used to decrypt it. In the environment of PKC, each user owns a pair of cryptographic keys: a public key and a corresponding private key. The public key is widely published, whereas the private key is kept secret by its proprietor. Although the public key and the private key are related mathematically, the system parameters will be chosen such that the private key is either impossible or prohibitively expensive to be obtained from the public key. Meanwhile, the secret channel between the sender and the receiver to share secret information is also eliminated since only public keys are involved in all communication while no private key is ever shared or transmitted. An overview of PKC is shown in Figure 1.2.