What is a Public Key - Beginner's Guide

Roland Säde
| Editor:
July 17, 2023
9 min read

In an era where data privacy is paramount, public key encryption has emerged as a remarkable technology that revolutionizes how we interact and secure critical information. Understanding the fundamentals of public key encryption is crucial in today's environment, where data breaches and unauthorized access pose significant threats. This comprehensive article highlights the intricacies of public key encryption, highlighting its importance in modern communication and unveiling the inner workings that make it a reliable and robust security mechanism.

Public key or asymmetric encryption is vital in securing sensitive data and facilitating secure communication over digital networks. Unlike traditional symmetric encryption, where the same key is used for both encryption and decryption, public key encryption employs two mathematically related keys - a public key and a private key. These keys work in tandem to ensure the transmitted information's confidentiality, integrity, and authenticity.

Public key encryption is an incredible technology that has transformed how we interact by providing a dependable way to secure critical data. In today's environment, where data privacy is critical, understanding the basics of public key encryption is vital. This article seeks to provide a thorough explanation of public key encryption, emphasizing its importance in modern communication and providing light on how it functions behind the scenes.

Encryption with a Public Key vs. a Private Key

Before delving into the intricacies of public key encryption, it's critical to understand the distinction between public and private key encryption. A single key is used for encryption and decryption in private key encryption, also known as symmetric encryption. While this method is straightforward and efficient, securely transmitting the encryption key between parties presents considerable obstacles.

Public key encryption, also known as asymmetric encryption, on the other hand, is based on a pair of mathematically related keys: the public key and the private key. The public key is freely distributed, while the private key is kept private and secure by the key owner. In contrast to private key encryption, public key encryption does not require key exchange, making it the preferred technique in many instances.

What is a public key, exactly?

A public key is a one-of-a-kind mathematical value generated with its matching private key. It is critical in public key encryption. Anyone who needs to securely communicate with the key owner can access the public key. However, extracting the private key from the public key alone is extremely difficult due to the computational complexity involved.

Encryption requires the use of a public key. When a sender wants to communicate information to a receiver securely, they encrypt the material with the recipient's public key. While anybody can use the public key to encrypt data, only the corresponding private key can decrypt the encrypted data.

What is a private key, exactly?

Unlike the public key, the key owner keeps the private key private. It is used to decrypt data encrypted using the associated public key. Keeping the private key secure is critical since illegal access to encrypted data is possible if it falls into the wrong hands.

Like the public key, the private key is generated using complicated mathematical processes. This procedure ensures great security by making it nearly impossible for an attacker to determine the private key from the public key and vice versa.

What exactly is Public Key Encryption?

In public key encryption, both the public and private keys are used in mathematical computations. The method has two stages: encryption with the public key and encryption with the private key.

Using a Public Key for Encryption

When a sender wishes to transmit an encrypted message to a recipient, the information is encrypted using the recipient's public key. Complex algorithms are used in this encryption process to convert plain text into unreadable encrypted text. Only the recipient's corresponding private key can decrypt the encrypted data correctly.

Using a Private Key for Encryption

Alternatively, the sender might use their private key to encrypt data. However, rather than preserving message confidentiality, the primary goal of this encryption strategy is to provide a means of validating the sender's identity. The recipient can authenticate the sender's legitimacy by decrypting the encrypted communication with the sender's public key. Decryption success confirms that the private key holder sent the communication.

The Benefits of Public Key Encryption

Because of its multiple advantages, public key encryption is the favored approach in many security-conscious applications. For starters, eliminating the requirement to share a single secret key solves the key exchange difficulty associated with symmetric encryption. This makes it easier for parties to communicate securely and share information.

Furthermore, public key encryption improves security. Because extracting the private key solely from the public key is computationally impossible, the public key can be freely disseminated without jeopardizing communication confidentiality. Even if an attacker intercepts the encrypted data, they can only decrypt it if they can access the accompanying private key.

Public key encryption also allows for digital signatures, which verify communication's validity and integrity. By encrypting a communication with the sender's private key, recipients can decrypt it and use its public key to verify its origin and integrity.

Usage of Public Key Encryption Examples

Public key encryption has practical uses in various real-world scenarios, emphasizing its significance. One common example is secure internet communication, such as email encryption or encrypted chat apps. Users can ensure that only the intended recipient can access and decode messages by encrypting communication with the recipient's public key.

Another example is digital signatures that use public key encryption. Digital signatures are essential for maintaining data integrity and non-repudiation, mainly when signing legally binding contracts or verifying software upgrades. By encrypting the message with the sender's private key, recipients can verify the message's validity and integrity using the sender's public key.

Making a Public Key

Creating a public key necessitates the use of specialized key-generation software. Complex mathematical procedures are used in these tools to generate mathematically related public and private key pairs. To maintain the security and integrity of the created keys, best practices should be followed during the key creation process.

SSH Public Key

Another common public key encryption application is Secure Shell (SSH) public key, which is used for secure remote server access. SSH enables users to connect to distant servers safely and conduct numerous administrative activities. SSH public keys are generated and used to authenticate and authorize remote users, providing additional security in addition to password-based authentication.

Users produce a public-private key pair on their local machine while using SSH. The public key is safely saved on the user’s local system, while the private key is uploaded to the remote server. This configuration allows for safe server access without sending credentials across the network.

SSH public keys can be generated with SSH key-generating software. These tools generate a public-private key pair using cryptographic algorithms. The public key is commonly stored in a file with the ".pub" extension, whilst the private key is safely stored on the user's machine.

Using a Public Key for Encryption and Decryption

The mathematical features of some algorithms, such as the widely used RSA (Rivest-Shamir-Adleman) algorithm, underpin the concept of public key encryption. As the name implies, the public key is made available to the public and can be freely distributed. On the other hand, the private key is maintained securely by the intended receiver or owner and must never be disclosed.

When Alice wishes to send a secure communication to Bob, she obtains Bob's public key and encrypts the message with it. This encrypted communication can only be deciphered with Bob's private key, which he has. Even if the encrypted message is intercepted during transmission, it remains unreadable without the private key, maintaining the communication's confidentiality.

Public key encryption also allows for digital signatures, ensuring digital documents' integrity and authenticity. When Alice wishes to sign a document digitally, she creates a unique digital signature using her private key. Anyone with access to Alice's public key can verify this signature, indicating that the document was not tampered with and was truly signed by Alice.

The computational complexity of the techniques utilized is the fundamental strength of public key encryption. While encryption is a computationally demanding operation, decryption using the private key is much faster. Because an attacker cannot decrypt intercepted communications without the associated private key, this asymmetry permits safe communication at scale.

Encryption software is required to encrypt and decrypt data using a public key. This software securely encrypts data using the recipient's public key. Similarly, decryption software decrypts encrypted data using the recipient's private key. To ensure the security and integrity of the encryption process, it is critical to employ dependable encryption software and adhere to best practices for key management.

Public Key Management Best Practices

Managing public keys effectively is critical for guaranteeing the security and confidentiality of encrypted communication. Key rotation, which involves regularly rotating public and private key pairs, is recommended to limit the risk of key compromise. Furthermore, revocation processes should be in place to invalidate compromised or outmoded keys as soon as possible.

Implementing backup plans is critical to avoiding data loss in the event of a key loss or hardware malfunction. Regularly backing up public and private keys assures continuity and decreases the risk of losing access to encrypted data.


Public key encryption is an important part of protecting our digital communications and maintaining the confidentiality and integrity of sensitive data. Users may make informed decisions to safeguard their data by understanding the concepts of public and private keys, the encryption and decryption procedures, and the benefits and applications of public key encryption. Following best practices in generating, managing, and using public keys is critical for increasing the security of our digital interactions. For individuals interested in going deeper into this critical topic of information security, more resources such as online tutorials and technical documentation are accessible.

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