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Explain the principle of Public key cryptography
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1.Asymmetric algorithms rely on one key for encryption and a different but related key for decryption.

2.It is computationally infeasible to determine the decryption from encryption key and encryption algorithm.

3.Either of the 2 keys (related) can be used for encryption with the other used for decryption (In case of RSA algorithm)

4.A Public key encryption has following key ingredients:

$$\text{A) Encryption}$$

$$\text{B) Authentication}$$

a) Plaintext: This is a readable message or data that is feed into the algorithm as input.

b) Encryption Algorithm: The encryption algorithm performs various transformations on the plain text.

c) Public and Private Keys: This is a pair of keys that has been selected so that if one is used for encryption then the other is used for decryption.

d) Ciphertext: This is the scrambled message produced as output. It depends on the key and the energy algorithm used for a given message two different keys will produce two different ciphertext.

e) Decryption Algorithm: This algorithm accepts the ciphertxt and the matching key to produce original plaintext.

5.The essential steps are the following:

1. Each user generates a pair of keys to be used for encryption and decryption of the messages.
2. Each user places one of the two keys in a public register or other accessible file. This is the Public key.
3. The companion key is Private As shown in Figure 5.1 that each user maintains a collection of public keys obtained from others.
4. If Bob wishes to send a confidential message to Alice, Bob encrypts the message with Alice’s Public key.
5. When Alice receives message. She decrypts it using private key. No other recipient can decrypt the message because only Alice knows the private key.

6.With this approach, all Participants have access to Public keys and Private keys are generated locally by each participants.

7.Never distributed, as long as users private key remains protected and secure, incoming accumulation is secure.

8.At any time system can change its private key and intimate companion, public key to replace old public key.