Public vs. Private Key Encryption: A Detailed Explanation

According to the 2023 Hybrid Security Trends Report, only 67% of organizations use encryption to protect their data in the cloud. Encryption is the process of encoding information in such a way that only authorized parties can read it. It is a critical tool in ensuring the confidentiality and integrity of sensitive information. Public key encryption and private key encryption are two types of encryption and each has its strengths and weaknesses. It’s important therefore to understand them, particularly if your organization is, or is considering, storing sensitive information. In this blog post, we will compare public and private key encryption and the role encryption keys play in safeguarding your most sensitive content.

Why Is Encryption Important?

The internet and cloud computing have created an exponential increase in content and much of it is sensitive. Customer records, contracts, financial information, research, clinical trials, and other information is digitized and stored in servers, rather than untethered PCs and file cabinets. Also, businesses use partners, vendors, contractors, and consultants to scale efficiently. With all this, cyber risks are mounting, and sharing this sensitive information with service providers is critical for success. Content encryption is an absolute necessity in email, file sharing, file transfer, and other communication channels to ensure confidentiality and integrity. Encryption helps protect against unauthorized access, theft, and tampering, making encrypted content more secure and less susceptible to data breaches, hacking, and cyberattacks. It is also essential for certain industries to demonstrate compliance with industry regulations and legal requirements.

Principles of Encryption

Encryption uses complex mathematical algorithms and principles to ensure the security of the encrypted content. To encrypt content, algorithms convert plaintext into ciphertext and protect it with an encryption key. To decrypt content, ciphertext is converted back into plaintext and requires a decryption key.

Here are some of the main mathematical principles behind encryption:

• Modular Arithmetic: A type of arithmetic that deals with positive integers and their remainders after division by a given modulus.
• Prime Numbers: A number that is divisible only by itself and 1.
• Number Theory: The branch of mathematics that deals with properties of numbers.
• Group Theory: The branch of mathematics that deals with symmetries and transformations of objects.

RSA Algorithm

The RSA algorithm is a widely used public key encryption algorithm. It is based on the principle that it is easy to multiply two large prime numbers, but hard to factorize the product of two large prime numbers into its factors. The RSA algorithm uses this principle to generate a public-private key pair, which can be used for encryption and decryption.

Diffie-Hellman Key Exchange Algorithm

The Diffie-Hellman key exchange algorithm is a method for securely exchanging cryptographic keys over an insecure channel. It is based on the principle of modular exponentiation, which makes it difficult for an attacker to calculate the secret key used for encryption and decryption.

Elliptic Curve Cryptography

Elliptic curve cryptography is a type of public key encryption that uses elliptic curves over finite fields to generate a key pair. It is more efficient than RSA and other public key algorithms, making it a popular choice for mobile devices and other resource-constrained environments.

Types of Encryption

There are two main types of encryption: symmetric encryption and asymmetric encryption (also known as public key encryption).

Symmetric Encryption

Symmetric encryption uses the same key for both encryption and decryption. The key must be kept secret to ensure the security of the encrypted data. Symmetric encryption is used extensively in protecting content at rest, such as hard drives and memory cards.

Asymmetric Encryption

Asymmetric encryption uses two keys, one for encryption and one for decryption. The encryption key (known as the public key) can be shared widely, while the decryption key (known as the private key) is kept confidential. Asymmetric encryption is used extensively in securing content over the internet.

Key Differences Between Public and Private Keys

Understanding the fundamental differences between public and private keys is crucial when evaluating public vs private key encryption strategies.

Technically, a private key is typically a large random number kept strictly secret by its owner. In contrast, a public key is mathematically derived from the corresponding private key using a one-way function; it’s computationally infeasible to determine the private key from the public key.

This mathematical relationship is the cornerstone of asymmetric cryptography. Key length and complexity also differ significantly: private keys for symmetric encryption (like AES-256) are relatively short (e.g., 256 bits), while public/private key pairs in asymmetric systems (like RSA or ECC) require much longer keys (e.g., 2048 bits for RSA or 256 bits for ECC) to achieve comparable security due to their mathematical structure.

Ownership and distribution mark another key difference between public key and private key systems. A private key must remain confidential and is never shared. A public key, however, is designed to be shared widely without compromising security. This simplifies key distribution for secure communication initiation but necessitates robust mechanisms (like Public Key Infrastructure, PKI) to verify the authenticity of public keys.

Security properties also diverge: private key encryption excels at confidentiality and speed, making it ideal for encrypting large volumes of data. Public key encryption primarily provides confidentiality, authentication (through digital signatures), and non-repudiation, essential for secure key exchange and verifying identities over untrusted networks.

Ultimately, the choice between public key encryption vs private key encryption often involves using both strategically: public key methods for secure key exchange and signatures, and private key methods for efficient bulk data encryption.

What Is Public Key Encryption and How Does It Work?

Public key encryption is an encryption method that uses a pair of keys, a public key and a private key, to encrypt and decrypt data, respectively. The public key is available to anyone who wants to send an encrypted message to the owner of the private key. It is used to encrypt the data and can be shared freely. The private key, conversely, is kept secret and is used to decrypt the encrypted message.

In public key encryption, a user generates a public-private key pair using a cryptographic algorithm. When a user wants to send a message to the owner of the private key, they use the public key to encrypt the message, which can only be decrypted using the private key.

Advantages of Public Key Encryption

Public key, or asymmetric, encryption offers several advantages over traditional symmetric encryption methods, including:

• Secure Communication: Public key encryption ensures that sensitive communication between two parties remains secure, even if intercepted by hackers. The public key is used to encrypt the message, and the recipient’s private key is used for decryption. This ensures that only the intended recipient can read the message.
• Confidentiality: Public key encryption ensures that confidential information is kept confidential and can only be accessed by authorized persons. This is especially important for sensitive information such as financial transactions, trade secrets, and other personal data.
• Scalability: Public key encryption is scalable to large numbers of users and can be used for secure communication among a large number of people. This makes it ideal for use in business environments, government agencies, and other organizations.
• Non-repudiation: Public key encryption provides non-repudiation, which means that the sender of a message cannot deny having sent the message once it has been sent. This is important in legal and financial scenarios where proof of identity and authenticity is required.
• Integrity: Public key encryption ensures the integrity of the message, which means that the message cannot be altered during transmission without being detected by the recipient. This ensures that the message remains intact and has not been tampered with.
• Convenience: Public key encryption is convenient to use. Unlike symmetric encryption, public key encryption does not require the exchange of keys before the communication. It is easy to use in web applications and for secure email communication, etc.

Limitations of Public Key Encryption

While public key encryption is a popular and powerful method of securing data and communications, it has its limitations. One of the main limitations of public key encryption is the potential for security breaches. If a hacker gains access to the private key, they can decrypt all the data that was encrypted with the corresponding public key.

Another limitation is the potential for man-in-the-middle (MITM) attacks, where an attacker intercepts communication and impersonates one of the parties to gain access to the private key. This can be prevented with proper authentication and verification protocols, but it adds complexity to the encryption process.

Additionally, public key encryption can be slower and more resource-intensive than other encryption methods, making it less suitable for large-scale data transfers or real-time communication.

What Is Private Key Encryption and How Does It Work?

Private, or symmetric, key encryption, is a type of encryption where the same key is used to both encrypt and decrypt the message. This means that the sender and recipient must have the same encryption key in order to communicate securely.

Private key encryption involves four steps:

1. Key generation: The sender and recipient each generate their own unique secret key that will be used for encryption and decryption.
2. Encryption: The sender uses the secret key to encrypt the message, transforming it into an unreadable format.
3. Transmission: The encrypted message is transmitted through a communication channel, such as the internet or a phone line.
4. Decryption: The recipient uses their secret key to decrypt the message, converting it back to its original readable format.

Advantages of Private Key Encryption

Private key encryption is a powerful tool that offers a range of benefits for businesses, organizations, and individuals. From enhanced security to improved scalability and flexibility, this encryption technique can provide a wide range of advantages for those who need to protect their sensitive information. Whether you’re sending emails, transferring files, or conducting web transactions, private key encryption can offer the peace of mind you need to know that your data is safe and secure. Let’s take a closer look at these advantages:

• Security: Private key encryption is one of the most secure forms of encryption available. It uses a unique key for encryption and decryption, which ensures that only the intended recipient can access the content.
• Confidentiality: Private key encryption protects the confidentiality of content by ensuring that only the intended recipient(s) can access the information.
• Efficiency: Private key encryption is a relatively fast and efficient way to encrypt content. It can encrypt and decrypt content quickly, making it suitable for use in real-time applications.
• Scalability: Private key encryption can be used to encrypt content on a large scale. It is an effective way to protect content in an enterprise or organization.
• Flexibility: Private key encryption is a flexible encryption technique that can be used in a variety of applications and environments. It is widely used in email, secure file transfer, and web transactions.
• Authenticity: Private key encryption provides authentication of data by ensuring that only the intended recipient can decrypt and read the data. This ensures that the data has not been tampered with or altered.
• Control: With private key encryption, the key owner has complete control over who can access their content. This makes it an ideal choice for individuals and organizations that need to protect sensitive information.

Limitations of Private Key Encryption

Private key encryption has its limitations. The main limitation is the issue of key exchange. As private key encryption uses the same key for encrypting and decrypting the message, the key must be shared between the sender and receiver. This creates a security risk because if the key is compromised, then all messages using that key are also at risk. Additionally, managing and storing keys securely can be a cumbersome task.

Another limitation is the scalability of private key encryption. As the number of users increases, the number of keys required also increases rapidly. Creating and managing keys for a large number of users can be challenging. Finally, private key encryption is vulnerable to brute-force attacks. As computing capabilities continue to increase, it becomes easier for attackers to guess keys and gain access to encrypted information.

Comparison Between Public Key and Private Key Encryption

There are several notable differences between public key encryption and private key encryption. The following table provides a comparative look at their main differentiators:

How Public and Private Keys Work Together

Public and private keys form the foundation of asymmetric cryptography, operating as a mathematically linked pair designed for distinct but complementary functions within the public private key encryption system.

The core principle lies in their generation: a complex algorithm creates a private key, and its corresponding public key is derived from it. While related, reversing the process—calculating the private key from the public key—is computationally infeasible with current technology. This one-way relationship allows the public key to be shared openly without risking the secrecy of the private key. In practice, they work in tandem.

For confidentiality, a sender encrypts a message using the recipient’s public key. Only the recipient, possessing the unique, corresponding private key, can decrypt and read the message.

Conversely, for authentication and integrity via digital signatures, the sender encrypts a hash (a unique fingerprint) of the message using their own private key. Anyone can then use the sender’s public key to decrypt the hash and verify that the message originated from the sender and hasn’t been altered.

Key exchange protocols like Diffie-Hellman or the initial handshake in TLS/SSL also leverage this pairing, allowing two parties to securely establish a shared secret key (often for faster symmetric encryption) over an insecure channel using public key cryptography.

Real-world examples abound: secure email (S/MIME or PGP) uses public keys to encrypt messages and private keys to decrypt or sign them; SSL/TLS certificates validate a website’s identity using its public key, enabling secure HTTPS connections through this coordinated use of public key encryption and private key operations.

Which Encryption Key Type Is Best for Your Business?

The choice between public key and private key encryption depends on your specific use case. If you need to secure communication between two parties who have never communicated before, or if you need to add new users to a secure communication network, public key encryption is the best choice. Alternatively, if you need to protect content at rest, such as sensitive emails and files, private key encryption is the best choice.

Which Encryption Key Type Is More Secure?

Both public key and private key encryption are secure in their own right. However, public key encryption is more vulnerable to attacks such as man-in-the-middle attacks and brute-force attacks. Private key encryption, on the other hand, is more vulnerable to attacks such as key distribution and insider attacks.

Threats to Public and Private Key Encryption

Public and private key encryption are not immune to compromise or cyber threats. Here are some of the main risks:

Man-in-the-Middle Attacks

In a man-in-the-middle attack, an attacker intercepts and alters communication between two parties, allowing them to eavesdrop on the conversation or manipulate the data.

Brute-force Attacks

A brute-force attack is an attack that tries every possible key until the correct one is found. It is an effective attack against weak keys and short key lengths.

Cryptanalytic Attacks

Cryptanalytic attacks are attacks that exploit weaknesses in the encryption algorithm to recover the plaintext from the ciphertext. They are typically more sophisticated than brute-force attacks and require knowledge of the algorithm.

Quantum Computing Threats

Quantum computers have the potential to break many of the public key cryptography algorithms in use today. They can solve complex mathematical problems, such as factoring large primes, much faster than classical computers.

Key Management Challenges and Best Practices

Effective encryption relies heavily on robust key management, but organizations face significant challenges in this area, particularly with private key encryption.

Secure key storage is paramount; storing keys alongside encrypted data or in easily accessible locations undermines the entire security posture. Best practice dictates using dedicated Hardware Security Modules (HSMs) or secure key vaults with strict access controls.

Key rotation—periodically changing encryption keys—is critical to limit the impact of a compromised key, yet implementing seamless rotation policies without disrupting operations can be complex.

Access control must follow the principle of least privilege, ensuring only authorized personnel and systems can manage or use keys, often enforced through Role-Based Access Control (RBAC).

Comprehensive backup and recovery procedures are essential to prevent data loss if keys are lost or corrupted, but backups must be as securely protected as the primary keys.

Managing the entire key lifecycle, from generation and distribution to eventual revocation and destruction, requires defined processes and automation to avoid errors.

Regulatory compliance mandates (like GDPR, HIPAA, PCI DSS) often impose specific requirements for key management, adding another layer of complexity.

Common mistakes include hardcoding keys in applications, using weak or default keys, and inadequate logging or auditing of key usage. Enterprise-level solutions like Key Management Systems (KMS) provide centralized control, automation, and auditing capabilities, addressing these challenges by enforcing policies and simplifying the secure administration of encryption keys throughout their lifecycle.

Applications of Public and Private Key Encryption

Encryption has become an integral part of digital communications. With the increase in online communication and transactions, keeping sensitive data secure has become more important than ever. Public and private key encryption are powerful tools that offer a secure way to transmit data over the internet. Some of the applications of public and private key encryption include:

Secure Communications

Public key encryption is used extensively in securing communication over the internet. It is used in protocols such as SSL/TLS, SSH, and PGP.

Digital Signatures

Digital signatures are used to verify the authenticity of messages and documents. They use public key encryption to ensure that the signature can only be created by the owner of the private key.

SSL/TLS Certificates

SSL/TLS certificates are used to secure web traffic. They use public key encryption to ensure that the certificate can only be issued by the owner of the private key.

Secure File Sharing

Public key encryption is used in secure file sharing applications such as Dropbox, Google Drive, OneDrive, and Kiteworks.

Virtual Private Networks

Virtual private networks (VPNs) use encryption to create a secure tunnel through an insecure network, such as the internet. They use public key encryption to negotiate the encryption keys.

Real-World Examples of Encryption Implementation

Public and private key encryption are ubiquitous in the digital world, securing sensitive information across various sectors.

In Banking and Finance, online transactions and mobile banking apps rely heavily on TLS/SSL protocols, which use public key encryption (like RSA or ECC) for the initial secure handshake and authentication, followed by faster private key encryption (like AES) for securing the actual session data. Payment processing often employs tokenization and end-to-end encryption.

The Healthcare industry uses encryption to comply with regulations like HIPAA. Electronic Health Records (EHR) systems frequently use AES-256 private key encryption to protect patient data at rest, while secure patient portals utilize TLS (employing both public and private key techniques) for confidential communication.

Government and Military applications often involve highly sensitive data, protected by robust, often classified, encryption algorithms, sometimes including custom implementations alongside standards like AES and public key infrastructure for secure identification and communication.

Consumer applications like secure messaging apps (e.g., Signal, WhatsApp) implement end-to-end encryption, typically using protocols that leverage public key cryptography (like the Signal Protocol) for key exchange and symmetric encryption for message confidentiality.

Password managers often use strong symmetric encryption (AES-256) to protect the stored vault, secured by a master password.

Enterprise implementations include corporate VPNs (using IPsec or SSL/TLS) which establish secure tunnels using a combination of public and private key techniques, and secure email systems like PGP or S/MIME which use public keys for encryption/verification and private keys for decryption/signing.

Cloud Service Providers (AWS, Azure, Google Cloud) offer extensive encryption options, including encryption at rest (often AES-256) and in transit (TLS), allowing customers to choose between provider-managed or customer-managed keys, integrating both public private key encryption principles for comprehensive data protection.

Kiteworks Helps Organizations Protect Their Most Sensitive Content With Automated, Double Encryption

Kiteworks provides a secure, encrypted Private Content Network for secure file sharing, collaboration, and communication. One of the key features of Kiteworks is its double encryption.

Kiteworks’ first encryption layer is done on the end-user’s device. Files are encrypted using AES-256 encryption before they even leave the device. This ensures that files are secure from the outset and cannot be accessed by unauthorized users. The second layer of encryption is done on the Kiteworks hardened virtual appliance. This layer of encryption adds an extra level of protection to files that are already encrypted. This double encryption system provides an extremely high level of security and ensures that files are protected at all times.

Kiteworks’ deployment flexibility allows organizations to choose between on-premises, cloud, hybrid, or FedRAMP virtual private cloud deployment options. This gives organizations the ability to customize their deployment to meet their specific security and regulatory compliance requirements. Customers own their own encryption keys, ensuring that nobody, not even Kiteworks, can access their sensitive content. This added layer of security provides peace of mind and full control over content protection.

In addition to file sharing and collaboration, Kiteworks also encrypts emails via an Email Protection Gateway. Emails containing sensitive information can be securely sent and received within the Kiteworks platform. The Email Protection Gateway encrypts emails using PGP encryption, ensuring that only the intended recipient can access the email. This feature is particularly useful for businesses that need to send sensitive information via email.

Kiteworks’ automated encryption makes it easy to use for both end-users and IT administrators. The encryption process is seamless and transparent, with users not even noticing that their files and emails are being double-encrypted. This ensures that sensitive content is always protected without any extra effort required from users. Additionally, IT administrators can easily manage and monitor the encryption process from a centralized dashboard, giving them full visibility and control over content protection.

For organizations seeking to see the Kiteworks Private Content Network and its encryption capabilities in action, book a custom demo today.

Additional Resources

• Brief Kiteworks Hardened Virtual Appliance Provides Multiple Security Layers to Dramatically Reduce Vulnerability Exploit and Impact Severity
• Webinar How Automated Encryption Delivers Improved Privacy Protection and Compliance
• Brief Expand Visibility and Automate Protection of All Sensitive Email
• Blog Post Secure File Sharing Encryption: How to Keep Your Data Safe and Secure
• Video Kiteworks Email Protection Gateway (EPG) Automates Email Encryption and Decryption