**Asymmetric Key Cryptography**

**Asymmetric key cryptography**is also called a public key cryptography.- In
**Asymmetric key cryptography**two keys are used, one for encryption and other for decryption. **Asymmetric key cryptography**involves the use of two keys one is a public key that may know to everyone and can be used to encrypt messages and verify signatures. Other is private key known only to the receiver of the message or verifier, used to decrypt messages, and sign (create) signatures.- It is also called as asymmetric key cryptography because one key is used for encryption only its corresponding key must be used for decryption. No other key can decrypt the message.
- The sender and receiver can encrypt messages using encryption key (public) or verify signatures, he cannot decrypt messages or create signatures because he required decryption key (private) which is known only to the receiver of the message. Public key cryptosystem /asymmetric key cryptography is shown in Fig.

- Mathematically it is represented as
**P=D(Kd, E(ke, P))** **For Example**, Sender Ramesh wants to communicate with the receiver Suresh then they must have each one of this i.e private key and public key then and then Communication will be successful Table shows the possible pair of keys that Ramesh and Suresh must know while communicating with each other.

Key Details | Ramesh (A) Should know | Suresh(B) Should know |
---|---|---|

Ramesh Private Key (A) | Yes A mast know. | Not known to B |

Ramesh Public Key (A) | Yes A must know | Yes it is known to Suresh also |

Suresh private key (B) | Not known to Ramesh (A) | es Suresh (B) must know |

Suresh public key (B) | Yes known to Ramesh (A) | Yes Suresh (B) also known it |

- Following are the possible cases of public key cryptography as per the table mentioned

above.

**Case 1 **

- When Ramesh wants to send a message to Suresh. Ramesh can encrypt the message using Suresh public key. This is possible because Ramesh and Suresh know the public key.
- Ramesh can send this message to Suresh (Keep in mind this it is encrypted using Suresh public key).
- Suresh can decrypt the Ramesh message by using Suresh own private key. Because only Suresh knows his private key Ramesh is not aware of Suresh private key.
- It is important to note that the message only decrypted using Suresh private key and nothing else.

**Case 2**

- If Suresh wants to send the message to Ramesh, then reverse the above case I. Suresh can encrypt the message only with Ramesh public key. The reason only Ramesh can decrypt the message to obtain its original plain text format using his private key.
- Public key cryptography achieves authentication (authentication helps to identify the claimed identity of an entity, such as username password or any other important information such as encryption or decryption keys stolen during transmission between sender and receiver) and non-repudiation (it prevents either sender or receiver from denying a transmitted message).
- Principles of public key cryptography also include mathematical background to understand the use of key pairs in algorithms like Rivest Shamir Adlman (RSA)and Diffie Hellman Algorithm.
- For Example: Rivest Shamir Adlm. (RSA) and Diffie Hellman key exchange algorithm.

**Advantages of Asymmetric Key Cryptography**

- In Asymmetric key cryptography, key cannot be distributing among sender and receiver as both have their own key, so there is no problem of key distribution while transmitting the data over insecure channel.
- The main advantage of asymmetric key cryptography is that two separate keys are used for used encryption and decryption; even if encryption key is stolen by attacker he/ she cannot decrypt the message as decryption key is only available with receiver only.
- RSA algorithm and Diffie Hellman key exchange are implemented using asymmetric key cryptography.
- Easy to use for user and scalable does not require much administrative work.

**Disadvantages of Asymmetric Key Cryptography**

- Because of a different key used between sender and receiver require more time to get the transmission done as compared to symmetric key cryptography. (Slower that symmetric key cryptography very few asymmetric encryption methods achieve the fast transmission of data).
- Asymmetric key cryptography utilizes more resource as compare to symmetric key cryptography.

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