# Asymmetric Key Encryption

Introduction: – In the earlier tutorial you have learned about the symmetric key encryption and also saw some of the examples and algorithms associated with it. In this tutorial, you will see another type of encryption technique – the asymmetric key cryptography. These techniques are also dependent on the number of keys used and in which form.

Asymmetric Key Cryptography: –
Asymmetric Key Encryption: These are special encryption technique which is having 2 keys, the public and the private key. With the increase in less secured networks and information sharing options from the last decades, there lays a genuine need for large scale security of information. So there comes the role of asymmetric encryption, which is a different kind of encryption with pair of keys. In this pair of keys, one key encrypts while the other decrypts and the keys are interchangeable, which means if key “alpha” can encrypts, then key “beta” will be used to decrypt, and if key “beta” is used to encrypts then key “alpha” can be used to decrypts.

Asymmetric key encryption is also termed as Public key cryptography because users are mainly involved in matching key pair in creating a public key and at the same time keep the other key as secret. Encrypted messages can be signed in and read by encrypting them with their private keys. The technique becomes effective as verification becomes easy to prove that the secret key was used to encrypt it. If the secret key is genuinely secret, then it becomes assured that the actual user have sent the message and not any impostor or unauthorised person.

Here’s a diagram of how asymmetric key cryptography works –

Mathematical representation of Asymmetric ciphers: –
The system of asymmetric encryption consists of three algorithms (K, Enc, Dec):
K ( ) – the nondeterministic algorithm that gives back a pair of keys (s k , p k ),
Enc ( p k, i) – the nondeterministic algorithm that is used for encrypting plain text i (information) and gives output as cipher text c,
Dec (s k , c) – the deterministic algorithm that is used for decrypting cipher text c and outputs the plain text i.

The 3 algorithms must offer reliability because each pair of keys (s k , p k ) formed by algorithm K &amp; for every i, i.e. the plain text message, following situation must be satisfied:

Dec (s k , Enc (p k , i) ) = i

It is possible for intruders to grab any message. Hence asymmetric ciphers are more vulnerable to chosen plain text attacks, where the cryptanalyst arbitrarily chooses a plain text for encryption for receiving the corresponding cipher text. Asymmetric key cryptographic algorithms are slower in comparison to symmetric key cryptographic algorithms.
Examples of Asymmetric key cryptographic algorithms are: –

• Diffie-Hellman’s protocol
• Merkle’s puzzle
• RSA etc.