**Introduction**

Different
keys are used for encryption and decryption, it is called **asymmetric key
cryptography. **Public key used for encryption, private key used for decryption
and vice versa. It is also known as **public key cryptography**.

**Requirement of Public Key
Cryptography**

It is ** computationally
easy for party B** to generate the key pair

*(PU*_{b}and PR_{b})It is ** computationally
easy for a sender A**, knowing the public key and the message to be
encrypted, M, to generate the corresponding ciphertext.

*C = E (PU*_{b}, M)It is ** computationally
easy for the receiver B** to decrypt the resulting ciphertext using
private key to recover the original message.

*M = D (PR*_{b}, C) = D (PR_{b}, E (PU_{b}, M))It is ** computationally
infeasible for an attacker**, to determine private key from known public
key.

It is ** computationally
infeasible for an attacker**, to recover original message from known
public key and cipher text.

**Cryptanalysis of Public Key
Cryptography**

Public
key encryption method is accessible to the brute force attack.

Public
key method depends on the use of mathematic equation or some function.

** Key size
is larger** enough to avoid brute force attack.

When key
size is large ** then speed of encryption/decryption are too slow**.
This key is generating for to make brute force attack impractical.

Public
key encryption is bound to ** signature application and management**.

If
attacker have public key of receiver and he/she try to calculate private key,
but it is not confirmed that this type of attack is feasible for a particular
public key algorithm.

**To learn more about Requirement and Cryptanalysis of PKC, Click here**

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