Public-Key Cryptography

May 20, 2023

Public-key cryptography, also known as asymmetric cryptography, is a type of encryption that uses a pair of keys, a public key and a private key, to secure communication and data transfer over the internet. Public-key cryptography is widely used in various web-related applications such as online banking, secure email, and secure browsing.

The purpose of public-key cryptography is to enable secure communication between two parties without the need for them to share a secret key. In traditional symmetric cryptography, both parties have to share a secret key that is used to encrypt and decrypt the message. However, this approach has some limitations such as the need for a secure channel to exchange the secret key, difficulty in managing and updating the shared key, and the risk of key compromise if the shared key is stolen or intercepted.

Public-key cryptography overcomes these limitations by using two mathematically related keys, a public key and a private key, to encrypt and decrypt the message. The public key can be freely distributed and used by anyone to encrypt the message while the private key is kept secret and used only by the intended recipient to decrypt the message. This approach provides a higher level of security and eliminates the need for a secure channel to exchange the key.

How does Public-key Cryptography work?

Public-key cryptography is based on the principles of number theory and mathematical algorithms. The two keys, public and private, are mathematically related such that the message encrypted with one key can only be decrypted with the other key. The public key is generated by the recipient and made available to anyone who wants to send a message securely. The private key is kept secret and securely stored by the recipient.

When a sender wants to send a message to the recipient, they use the recipient’s public key to encrypt the message. The encrypted message can only be decrypted by the recipient using their private key. This ensures that only the intended recipient can read the message and that the message cannot be intercepted by an attacker.

Public-key cryptography also allows for digital signatures, which provide a way to verify the identity of the sender and the integrity of the message. To create a digital signature, the sender uses their private key to encrypt a message digest, which is a fixed-length representation of the original message. The recipient can then use the sender’s public key to decrypt the signature and verify the message’s authenticity.

Applications of Public-key Cryptography

Public-key cryptography is widely used in various web-related applications to provide secure communication and data transfer. Some of the most common applications of public-key cryptography are:

Secure Browsing

Secure browsing is a technique used to protect online transactions and sensitive data from unauthorized access. Public-key cryptography is used to establish a secure connection between the client and server, which encrypts all the data transferred between them. The most common protocol used for secure browsing is HTTPS (Hypertext Transfer Protocol Secure), which uses public-key cryptography to encrypt the communication between the client and server.

Email Encryption

Email encryption is a technique used to protect the privacy of email messages by encrypting them before they are sent over the internet. Public-key cryptography is used to encrypt the email message, and the recipient’s private key is used to decrypt the message. The most common standard for email encryption is Pretty Good Privacy (PGP), which uses public-key cryptography to encrypt the email message and digital signatures to verify the sender’s identity.

Digital Signatures

Digital signatures are used to verify the authenticity of a digital document or message. Public-key cryptography is used to generate a digital signature, which is a mathematical representation of the document or message that can be used to verify its authenticity. Digital signatures are widely used in online transactions, electronic contracts, and other applications where it is essential to verify the authenticity of the document or message.

Online Banking

Online banking is a popular application of public-key cryptography, where it is used to secure online transactions and protect sensitive data such as login credentials, account information, and transaction details. Public-key cryptography is used to encrypt the communication between the client and server, which ensures that the data transferred over the internet cannot be intercepted or modified by an attacker.

Virtual Private Networks

Virtual Private Networks (VPNs) are used to provide secure access to a private network over the internet. Public-key cryptography is used to establish a secure connection between the client and server, which encrypts all the data transferred between them. This ensures that the data transferred over the internet cannot be intercepted or modified by an attacker.

No need to share a secret key

In traditional symmetric cryptography, both parties have to share a secret key that is used to encrypt and decrypt the message. However, in public-key cryptography, each party has their own key pair, and there is no need to share a secret key. This eliminates the need for a secure channel to exchange the key and reduces the risk of key compromise.

Digital signatures

Public-key cryptography allows for digital signatures, which provide a way to verify the identity of the sender and the integrity of the message. This ensures that the message has not been modified during transmission and that the sender is who they claim to be.

Scalability

Public-key cryptography allows for secure communication between multiple parties, making it ideal for large-scale applications such as online banking, e-commerce, and virtual private networks. Public-key cryptography also allows for secure communication between parties who have never communicated before, as there is no need to exchange a secret key beforehand.