Public Key and Private Key Pairs: What are they and How do they Work?

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What is Public Key and Private Key Pairs

A Beginner’s Guide to Understanding Public Key and Private Key Pair Cryptography

The primary component in public key cryptography is the combination of private and public keys. Both the keys come in pairs. So a public or private key will only function with the associated public or private key. It means that one private key can only have one public key and vice versa.

Before we get into the part where we explain how the combination works, let us first discuss each of the keys individually. Let’s start with the private key first.

What is a Private Key?

A private key is a piece of information used to decrypt and encrypt data, forming an integral part of a cryptographic system used to secure communication, protect data, and verify the authenticity of messages.

As a thumb rule, one should share public keys in the open but keep private keys confidential. When someone wants to send encrypted data to the owner of a private key, they use a public key to encrypt the message. So just the owner of the private key has the ability to decipher the message because they possess the private key.

Anyone with a private key can decrypt sensitive information transmitted over an encrypted connection. Therefore, people often store private keys on secure servers or devices and may protect them with additional layers of security, such as passwords or biometric authentication.

Understood what private key encryption is? Let us now discuss what a public key is.

What is a Public Key?

In cryptography, a public key is a piece of information that people use to encrypt data and verify the authenticity of a message or document.

In a cryptographic system that uses a public key, a parallel private key is used to decrypt messages or data encrypted using the public key. People can freely share the public key, but they must keep the private key secret. By using the public key for encryption of the message, a person can send encrypted data to the owner of the private key. This way, just the private key owner can decrypt the message because they are the only ones with access to the private key.

Now that we know what private and public keys mean individually, let us understand what a pair of public and private keys are.

What are Pairs of Public and Private Key?

As discussed already, a public-private key pair is a set of two unique keys used for symmetric and asymmetric encryption and decryption of data. There is a private and parallel public key in a cryptographic system that uses a pair of public and private keys. The private key stays confidential and is used for decrypting messages or encrypted data using the parallel public key. On the other hand, people can freely share the public key and use it to encrypt messages or data intended for the private key owner.

It is important to ensure that the correct public key is used to encrypt a message or document, as only the parallel private key will be able to decrypt the message. Similarly, it is important to keep the private key secure and protect it from unauthorized access, as anyone with access to it would be able to decrypt sensitive information transmitted over an encrypted connection.

So how do they work to establish security? Let us discuss that.

How do a Pair of Public and Private Key Work?

Let me provide an example of how a pair of public and private keys might be used to encrypt messages:

  • The sender generates a pair of public and private keys using the different forms of encryption algorithms such as RSA, DSA, and ECC (Elliptic Curve Cryptography). People keep the private key secret while they share the public key with the intended recipient.
  • For the sender to send an encrypted message, they will employ the recipient’s public key for the encryption of the message.
  • The sender sends the encrypted message to the recipient.
  • With the help of a private key, the recipient can decrypt the message, as the person with the private key is the one who can decrypt the message because it is the only key that can reverse the encryption process performed using the public key.

This is how the combination of a public key and private key encryption works. Now that we know they work, let us see how this combination benefits the security of data on the internet.

What are the Benefits of Public-Private Key Pair?

People use public and private keys in public key cryptography, a method of secure communication that allows them to exchange messages without needing to agree on a shared secret key in advance. The benefits of pair of public and private keys include the following:

● Security

The pair of public and private keys helps to protect communication by allowing people to encrypt messages with a public key and decrypt them only with the parallel private key. This means that only the private key owner can decrypt the message, providing a high level of security.

For example, Mike has some confidential information that he wants to send to Dustin. However, he wants to ensure that only Dustin receives it. For that, he will encrypt the information with the public key of Dustin, and since only Dustin can access the parallel private key, he can read and decrypt the encrypted information and access the information.

In this case, even if someone other than Dustin gets access to the encrypted information, it will still remain unreadable as they would not have access to the private key that only Dustin has.

● Non-Repudiation

 A pair of public and private keys can help to establish non-repudiation, which is the ability to prove that a specific sender sent a particular message and cannot be denied by that sender.

Let’s consider the example above to understand how to use a pair of public and private keys for non-repudiation.

Mike wants to send confidential information to Dustin. But in this case, Dustin wants to make sure either Mike or Dustin himself cannot deny the information. So Dustin can use Mike’s public key to encrypt the information and then send the encrypted message to Mike. So, only Mike, who has the parallel private key, can decrypt the message and read it.

Therefore, someone who had access to Mike’s public key could have only sent the message, allowing only Mike to decrypt it using his private key and providing proof of the message’s origin. If Mike refuses to receive any information, Dustin can show the encrypted message and Mike’s public key to prove the message’s origin and authenticity, serving as evidence that someone sent the information.

In this way, using a pair of public and private keys enables establishing non-repudiation by providing evidence that a specific sender sent a message, and the sender cannot deny it. This can be useful in cases where it is important to establish the authenticity of a message.

● Convenience of Application

 A pair of public and private keys can make secure communication easier to use because they allow users to exchange messages without needing to agree on a shared secret key in advance. This can be particularly useful in cases where it is difficult to securely exchange a secret key, such as when the users are located in different countries or when the users do not have a secure way to communicate.

Let’s take the same example of Dustin and Mike. The scenario remains the same. But in this case, Mike and Dustin need not exchange a secret key in advance or look for a secure way of communicating the key. Rather, they can use the public-private key for securely exchanging messages. This process can reduce the risk of key management problems and make it easier for users to use secure communication.

● Scalability

A pair of public and private keys can help make secure communication scalable because they allow many users to exchange messages without the need to agree on a shared secret key for each pair of users.

Traditional symmetric key cryptography uses a shared secret key for encrypting and decrypting messages. This means that each pair of users who want to communicate securely with each other must exchange and agree upon a separate secret. However, cases where a large number of people were involved in communicating securely, proved to be time-taking and impractical with this process.

In contrast, public key cryptography facilitates users to exchange messages using a public-private key pair. The public key encrypts the message, and the private key decrypts it. This means that each user only needs to share their public key with others instead of agreeing on a separate secret key for each pair of users.

For example, suppose a group of 1000 users wants to communicate securely. With traditional symmetric key cryptography, this would require the exchange and agreement of 99000 secret keys (one for each pair of users). However, with public key cryptography, each user would only need to share their public key with the other 990 users, making it much more scalable.

This can make it more practical and efficient to use secure communication in large systems.

Where is Public-Private Key Pair Used?

Many cryptographic protocols use public and private keys to transmit data between two parties securely. In these protocols, one party (typically called the sender) has a private key to encrypt data, and the other party (typically called the receiver) has a parallel public key to decrypt the data.

Many other applications use a pair of public and private keys, including:

● Secure Socket Layer (SSL)

Secure Sockets Layer (SSL) protocol is a common application of a pair of private, public keys for securing communications over the web. These protocols use public and private keys to launch a secure connection between the central server and the client-server.

● Digital Signatures

A digital signature is responsible for verifying the authenticity and integrity of software or digital file. It works by using a private key to develop a distinct signature for the file, which can then be verified using the parallel public key. The basic idea is to use a private key to create a unique signature for a piece of information and a corresponding public key to validate the information’s authenticity and integrity.

● Encrypting and Signing Emails

Email encryption, a process to securely send and receive emails, can use a pair of public and private keys. Email encryption works by using a private key to encrypt the content of an email message and a public key to decrypt it. In addition to encrypting the content of the data, the sender can also create a digital signature of the data by using their private key. Thus, the recipient can validate the information’s authenticity and integrity as well as the sender’s identity.

● Authenticating SSH connections

The Secure Shell (SSH) protocol is a secure network protocol that launches secure connections between servers. With the help of public-key cryptography, SSH authenticates the remote computer and paves the way for remote computers to authenticate the user. In this process, the user generates a pair of public and private keys and then installs their public key on the remote computer. After this process, the user begins an SSH connection to the remote computer. Later, by using their public key, the remote computer validates the user.

Implementing public-key authentication for SSH involves many technical details in practice, but the basic idea is to use the user’s private key to authenticate them to the remote computer, and the remote computer uses the corresponding public key to verify the user’s authenticity.

● Ethereum and other Blockchain Platforms

Ethereum and other blockchain platforms widely use a pair of public and private keys to sign transactions and prove ownership of a blockchain account securely.

In these platforms, users generate a pair of public and private keys and install their public keys on the blockchain. Then, when the user wants to send a transaction on the blockchain, they use their private key to sign the transaction. After broadcasting, the network verifies the signed transaction using the user’s public key. The network processes the transaction if the signature is valid.

The user signs the transaction with their private key to prove the ownership of their blockchain account. The network uses the parallel public key to establish the authenticity and integrity of the transaction. These platforms use a pair of public and private keys to sign transactions securely.

These are some of the places where public-private keys are used.

Stay Encrypted, Stay Safe!

A private and public key pair is a set of two keys you use to encrypt and decrypt confidential information on the web. Thus, they make for robust encryption and data security. Leveraging this pair of keys, you can enjoy seamless, enhanced security. We hope the blog gives you an idea about private and public keys and how it is instrumental in keeping the data safe and secure.

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Janki Mehta

Janki Mehta

Janki Mehta is a Cyber-Security Enthusiast who constantly updates herself with new advancements in the Web/Cyber Security niche. Along with theoretical knowledge, she also implements her practical expertise in day-to-day tasks and helps others to protect themselves from threats.