What is Public Key Cryptography?

What is Public Key Cryptography?

You have most likely been exposed to cryptography in some form or another. Signing messages, encrypting payloads, validating signatures, and employing certificates are all functionalities we use daily without realizing it.

Public-key cryptography, also known as asymmetric cryptography, has been the subject of extensive scientific investigation since the mid-1970s. It continues to be the subject of several books and research articles to this day.

This article will explain the essential functional principles behind Public-key cryptography and offer examples of applying them.

History of Public Key Encryption

During the early days of cryptography, parties involved would rely on a key to communicate through a safe non-cryptographic mechanism such as a face-to-face encounter or a trusted courier. This key, which both parties must keep strictly confidential, might then send encrypted messages. With this technique of key distribution, a number of severe practical challenges occur.

Public Key Encryption

When two parties interact, the comprehensible or intelligible communication, known as plaintext, is turned into random garbage (referred to as ciphertext) for security concerns.


The process of converting plain text into cipher text is called encryption. An algorithm and a key are used in the encryption process. The key is a value that is distinct from the plaintext.

Two fundamental factors determine the security of traditional encryption:

  1. The Encryption algorithm
  2. Secrecy of the key

Once the ciphertext has been generated, it may be transferred. Depending on the key used at the moment, the encryption technique will yield a different result. Changing the key alters the algorithm’s output.

When the ciphertext is received, it may be converted back to plaintext using a decryption technique and the same key used for encryption.


Decryption is the opposite process of encryption.  It is the process of converting the ciphertext to plaintext.

Public Key Encryption:  

Asymmetric or public-key encryption is a type of cryptosystem in which encryption and decryption are conducted using different keys: public-key (known to everyone) and private-key (Secret key). This is referred to as Public Key Encryption.

Difference between Encryption and Public-key Encryption:

Basis Encryption Public-key Encryption
Needed for Work:
  • The same algorithm and key are used for the dual purpose of encryption and decryption.
  • It is essential that the sender and the receiver share the key.
  • The pair of algorithm keys are used for encryption and decryption.
  • Both the parties need to have a set of matching keys. 
Needed for Security:
  • The key must be kept hidden.
  • If the key is kept hidden, it is nearly hard to decode the message.
  • It must be challenging to identify the key without knowledge of the method and samples of ciphertext.
  • One of the two keys must remain hidden.
  • It is nearly hard to read the message if one of the keys is kept hidden.
  • It must be impracticable to identify the other key without knowing the method, one of the keys, and samples of ciphertext.

Characteristics of Public Key Encryption: 

  • The public key is critical as it is challenging to determine the decryption key using just the cryptographic technology and encryption key.
  • Both keys (public or private) can be used for encryption, while the other is used for decryption.
  • The public key cryptosystem allows public keys to be widely disseminated, giving users a quick and convenient way to encrypt material and verify digital signatures. In contrast, private keys may be kept hidden, guaranteeing that only the owners of the private keys can decode the content and establish digital signatures.
  • RSA (Rivest–Shamir–Adleman) is the most extensively used public-key cryptosystem. The difficulty of determining the prime components of a composite number is the foundation of RSA.

Components of Public Key Encryption: 

  • Plain Text: 

This is a legible or intelligible message. As an input, this message is passed to the Encryption algorithm.

  • Cipher Text: 

The ciphertext is generated as a result of the Encryption algorithm. We can’t easily comprehend this message.

  • Encryption Algorithm: 

The encryption algorithm is used to transform plain text into ciphertext.

  • Decryption Algorithm: 

It takes the ciphertext and the matching key (Private Key or Public Key) as input and outputs the original plain text.

  • Public and Private Key: 

Either a private key (Secret key) or a public key (known to everyone), is used for encryption and decryption.

Weaknesses of the Public Key Encryption: 

  • Brute-force attacks are possible with public-key encryption.
  • This technique also fails when the user’s private key is lost, making public-key encryption the most susceptible.
  • Public Key Encryption is also vulnerable to a man-in-the-middle attack. A third party can disrupt public-key transmission and subsequently alter the public keys in this attack.
  • Suppose the user private key used for certificate production higher up in the PKI (Public Key Infrastructure) server hierarchy is compromised or mistakenly leaked. In that case, a “man-in-the-middle” attack is also conceivable, rendering any subordinate certificate unsafe. This is also a flaw with public-key encryption.

Applications of the Public Key Encryption: 

A public-key encryption system’s most apparent application is for encrypting communication to guarantee secrecy – a text that a sender encodes using the recipient’s public key and can only be decoded by the recipient’s matched private key.

  • Encryption/Decryption:

You may achieve secrecy by using Public Key Encryption. In this instance, the plain text is encoded with the receiver’s public key. This assures that the ciphertext cannot be deciphered by anybody other than the receiver’s private key.

  • Digital signature: 

To identify the authority of the sender a digital signature is used. In this situation, the sender encrypts the plain text using his private key. Since the receiver may only decode the ciphertext with the sender’s public key, this stage secures the sender’s authentication.

  • Key exchange: 

This method is used for key management as well as secure data transfer.


The Public Key Register contains the public keys of all users. If Y wishes to transmit a secret communication to Z, he must encrypt the message with Z’s public key. When Z receives the message from Y, it may use its Private key to decode it. Because only Z knows Z’s private key, no other person can decrypt the message. To learn more about Public-key cryptography, browse the best cyber security course in India and master several essential concepts of this cutting-edge technology.


Public-key or Asymmetric encryption is a cryptographic technique based on two keys, one public and one private. Asymmetric encryption is most commonly used for encrypting communications, message validation, and authentication.

Cryptography is a fascinating field still being researched today, providing a wealth of knowledge for curious minds. This article has attempted to convey the fundamental ideas underlying asymmetric encryption, albeit merely touching the surface of such a vast subject. Nevertheless, if your project requires encryption, remember the golden encryption rule: don’t roll your crypto.

There are several libraries and pre-implemented robust, secure, battle-tested algorithms available. Do a complete study and select those that already meet the requirements of your project. Before you depart, check out the Stanford advanced computer security program to better understand public-key cryptography. Great Learning offers online courses in association with Stanford University and other top-notch universities that you can attend within the comfort of your homes.

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