What is Public Key Cryptography and How Does it Work?
Public key cryptography is a fundamental component of Public Key Infrastructure (PKI). It enables secure data exchange, authentication, and integrity verification, making it essential for businesses looking to protect their data from malicious attacks.
In this guide, we explain how public key cryptography works so that you can confidently implement this security measure in your business. Nexus Smart ID PKI platform offers comprehensive protection and seamless integration into your business operations.
What is public key cryptography?
Public key cryptography, also known as asymmetric cryptography, uses a pair of keys for encryption and decryption. This pair includes a public key and a private key. The public key, which is openly shared, encrypts the data. The private key, kept secret by the owner, decrypts the data.
For example, imagine you need to send a sensitive business document to a colleague. You use their public key to encrypt the document before sending it. Your colleague receives the encrypted document and uses their private key to decrypt it. This ensures that only they can access the sensitive information.
What is a cryptographic key?
A cryptographic key is a string of bits that transforms readable data (plaintext) into an unreadable format (ciphertext) and back again using an algorithm. Plaintext is the original data or message you want to protect, such as a confidential business report. Ciphertext is the scrambled version of this data, which appears as random-looking data without the key to decrypt it.
Let’s say you need to send a confidential project code “project 123” to a colleague securely.
- Encryption: Using your colleague’s public key, the word “project 123” is transformed into a scrambled version by applying a mathematical operation. The result might be a string of numbers like “34 29 36 21 13 11 38 22 24 25”.
- Transmission: This scrambled version “34 29 36 21 13 11 38 22 24 25” is sent to your colleague. Even if someone intercepts this message, they won’t be able to understand it without the corresponding private key.
- Decryption: Your colleague uses their private key to reverse the scrambling process. The private key decrypts the string of numbers back to the “project 123”.
How does public key cryptography work?
There are five key steps in the process of sending and receiving data with public key cryptography:
Key generation
Key generation is where a pair of keys is created using a cryptographic algorithm. You will generate two keys: a public key and a private key. The public key is meant to be shared openly with anyone who wants to send you encrypted messages. The private key, however, must be kept secret and secure.
Key exchange
You and the recipient exchange public keys to establish a secure communication channel. Sharing public keys enables each of you to encrypt messages intended for the recipient using their public key.
Encryption
When someone wants to send you a secure message, they will use your public key to encrypt the data. For example, if your business partner wants to send you a confidential financial report, they will use your public key to convert the report from readable plaintext into unreadable ciphertext.
Sending encryption
The encrypted message, now in the form of ciphertext, is then sent to you over standard communication channels like email or secure messaging apps. Even if the message is intercepted, it remains unreadable and secure because it is encrypted.
Decryption
Once you receive the encrypted message, you will use your private key to decrypt it. The private key reverses the encryption process, transforming the ciphertext back into its original readable format. This allows you to access the secure information sent to you.
What are the applications of public keys?
Public key cryptography is essential for communication security. Here are a few of the ways it is used:
Encryption
The main use of asymmetric cryptography is to encrypt messages and data, ensuring that only authorised users can access the encrypted data. This is vital for protecting sensitive business information transmitted over the Internet or stored in databases.
Digital signatures
Digital signatures are cryptographic techniques used to verify the authenticity and integrity of digital messages or documents. They involve using a sender’s private key to encrypt a hash of the message, creating a unique digital fingerprint. The recipient uses the sender’s public key to decrypt this fingerprint and verify the message’s origin and integrity.
Imagine you are working on a contract that needs to be digitally signed and sent to a client. First, you calculate a hash of the contract using a cryptographic hash function. Next, you encrypt this hash with your private key to create a digital signature.
When your client receives the contract and signature, they use your public key to decrypt the signature, revealing the hash. By comparing this hash with their own recalculated hash of the contract, your client can verify its integrity and confirm that it originated from you and hasn’t been altered.
Secure Socket Layer
Secure Socket Layer (SSL) is a protocol used to secure communication over the Internet. It uses public key cryptography to establish a secure connection between your web browser and a server. When you access a website using SSL, the server sends its public key to your browser, which encrypts data before sending it. This ensures that only the server that possesses the corresponding private key can decrypt and access the transmitted information.
Transport Layer Security connections
Transport Layer Security (TLS) is the successor to SSL and provides enhanced security features. When your device connects to a server over TLS, the server sends its public key to your device. Your device then uses this key to encrypt data before sending it. This ensures that only the server, with its private key, can decrypt the data, safeguarding sensitive information like web pages, emails, and other data exchanged between user and server.
FAQs about public key cryptography
What are the 5 steps to public key encryption?
Public key encryption involves five steps: key generation, key exchange, encryption, sending encrypted data, and decryption.
How does RSA public key cryptography work?
RSA is a widely used public key cryptographic system that relies on the mathematical properties of large prime numbers. It generates a pair of keys: a public key for encryption and a private key for decryption.
Why can’t you decrypt with a public key?
Public key cryptography is designed to ensure that only the private key can decrypt the data. The public key is used solely for encryption, maintaining the security and confidentiality of the encrypted information.