Principles of Public Key Cryptography

Principles of Public Key Cryptography

BY SIFS India | March 02, 2022

Principles of Public Key Cryptography

Encryption is the process of scrambling data so that it is unreadable to anyone except those who possess a key that decrypts the data.

Decryption is the process of restoring data from its encrypted form. If a hacker has access to the key, they can decrypt the data they are given.

Encryption can be used to protect sensitive information from people who are not allowed to see the information, but only those who have the key.

Encryption and decryption are the two main methods of achieving confidentiality in an information system.

Encryption is the process of encoding messages to ensure confidentiality, while decryption is the process of decoding messages to ensure confidentiality.

Types of Cryptographic Algorithms

Cryptographic algorithms can be classified in a variety of ways. They will be classified based on the number of keys used for encryption and decryption, as well as their application and use. The three types of algorithms that will be discussed:

SKC (Secret Key Cryptography)

It is a type of symmetric encryption that uses a single key for both encryption and decryption. Mostly for the sake of privacy and secrecy.

The sender encrypts the plaintext with the key and sends the ciphertext to the recipient, as shown in Figure 1A. To decode the message and recover the plaintext, the recipient uses the same key. Secret key cryptography is also known as symmetric encryption since it uses the same key for both tasks.

The key must be known by both the sender and the recipient in this type of encryption; this is, after all, the secret. The distribution of the key is, of course, the most difficult aspect of this strategy

PKC (Public Key Cryptography)

It is also known as asymmetric encryption since it uses one key for encryption and another for decryption. Authentication, non-repudiation, and key exchange are the most common uses.

Generic PKC uses two keys that are mathematically connected, but knowing one key does not make determining the other key simple.

The plaintext is encrypted with one key, while the ciphertext is decrypted with the other.

The critical element to remember here is that it makes no difference whether the key is used first; both keys are required for the process to work, as shown in Figure 1B. This method is known as asymmetric cryptography since it requires a pair of keys.

One of the keys in PKC is designated as the public key, which can be distributed as widely as the owner desires.

The other key is known as the private key, and it is never shared with anybody else.  The sending of messages is simple under this method.

Let's say Rashmi wishes to convey a message to Dev. Dev decrypts the ciphertext with his private key after Rashmi encrypts some information with his public key.

This method might also be used to prove who delivered a message; Rashmi, for example, could encrypt some plaintext with her private key; when Dev decrypts the message using Rashmi's public key, he knows that Rashmi sent it (authentication), and Rashmi cannot deny it (non-repudiation).

Hash Functions

Uses a mathematical transformation to "encrypt" information in an irreversible way, resulting in a digital fingerprint. Message integrity is the primary purpose of this protocol.

Hash functions, also known as message digests or one-way encryption, are algorithms that don't require a key, as shown in Figure 1C.

Instead, a fixed-length hash value is calculated based on the plaintext, making it impossible to reconstruct the plaintext's contents or length.

Hash algorithms are commonly used to generate a digital fingerprint of a file's contents, which is frequently used to confirm that the file has not been tampered with by an intruder or virus.

Many operating systems also make use of hash functions to secure passwords. As a result, hash functions provide a means for ensuring a file's integrity.

Figure 1 - Type of Cryptography

Public and Private Key Encryption

One of the most important types of cryptography is public-key encryption.

Public-key encryption is an asymmetric key algorithm that consists of two keys. The public key is meant for encrypting data, while the private key decrypts data.

The keys are created in pairs, meaning that the public key can only decrypt messages encrypted by its corresponding private key. This type of encryption is also called asymmetric encryption because the keys are different lengths and one cannot be derived from the other.

The first step in this process is to find a number that satisfies some mathematical criteria (a prime number greater than 1, for example). This becomes your private key.

Next, you find another number that satisfies these same criteria but has a different value than your private key (e.g., 2). This becomes your public key.

You can then use your private key to encrypt any message and send it to anyone with access to your public key, and they will be able to decrypt it using their private key because they have both halves of the equation necessary for decryption.

What are The Benefits of Cryptography?

Cryptography is the practice and study of protecting information in order to make it unreadable to those who are not meant to see it.

Cryptography can be used to hide the contents of private conversations and emails, prevent identity theft, and prevent the identity of a document from being traced back to its creator.

It's a means of communication that is meant to be unreadable and indecipherable to anyone unless they have the key.

The benefits of cryptography include the ability to send private information in a way that's not open to the public, and to protect sensitive information.

There are many benefits of cryptography, one of which is that it can help protect information being sent and received. 

How Public-Key Encryption Works

Public-key encryption is a type of cryptography that uses two keys: a public key and a private key.

The public key encrypts the data, but it can only be decrypted by the corresponding private key.

This means that if someone wanted to decrypt the message, they would need your private key. The two keys can be thought of as one with two parts: one for encoding and one for decoding.

The encoding part is called the public key, and the decoding part is called the private key.

The benefit of this system is that anyone with access to your public key can encode information in such a way that only you can decode it with your private key.

And vice versa: anyone in possession of your private key will be able to encode information in such a way that only another person with access to their public key will be able to decode it.


Cryptography is an important part of modern life. It is used in the banking industry, to protect data on your computer, to encrypt messages sent via email, and is used in many other ways.

But not many people know how it all works. Now you know the basics of cryptography, and will be able to better understand how it works with the various applications that use it.

So, why are there so many different cryptographic systems to choose from? Why can't we just use one to do everything?

The explanation is that each method is tailored to a certain cryptographic task (s).

Hash functions, for example, are ideal for verifying data integrity since any change to the contents of a message will lead the receiver to calculate a different hash value than the one sent by the sender.

Data integrity is assured to a high degree of confidence because it is exceedingly rare that two separate messages will give the same hash value.

Secret key cryptography, on the other hand, is great for encrypting messages and ensuring privacy and confidentiality.

To encrypt the communication, the sender can produce a session key per message; the recipient, of course, requires the same session key to decrypt the message.

Of course, one of the most important applications of public-key cryptography is a key exchange (no pun intended).

Non-repudiation and user authentication can also be achieved via asymmetric techniques; if the receiver obtains the session key encrypted with the sender's private key, then only this sender could have sent the message.

Theoretically, public-key cryptography might be used to encrypt messages, but this is rarely done because secret key cryptography values can be computed 1000 times faster than public-key cryptography values.

So, How's your experience with learning a brief about cryptography? if you liked it and want to read more such blogs then click here to access more of our educational articles and blogs and enhance your knowledge on various topics of your interest.

Disclaimer- The images and information used in this article are for educational purposes only. 

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