Understanding Public Keys: Function and Operation Explained

In cryptography, a public key is a big number used for encrypting data. You can create it using software, but usually, a trusted authority generates it and shares it via a public directory.

Public key encryption uses two types of algorithms: symmetric and asymmetric. Symmetric encryption relies on a single key for both encrypting and decrypting data. In contrast, asymmetric encryption uses two keys: a public key for encrypting messages and a private key for decrypting them. The public key is often paired with a private key, generated through algorithms like RSA, elliptic curve cryptography, or the Digital Signature Algorithm. You can obtain public keys from a certificate authority, which issues digital certificates that authenticate the owner’s identity.

Let’s break down the four main components of public key infrastructure.

Now, how does public key encryption actually work? It involves using a key that acts as a mathematical algorithm, either in software or hardware, to encrypt and decrypt data. The key combines with the data to create ciphertext. You can use the same key for both encryption and decryption or apply different keys; that’s where public and private keys come into play.

The process of sending and receiving data through asymmetric cryptography involves five steps:

1. Key generation: Each person creates a public and private key.
2. Key exchange: They share their public keys.
3. Encryption: The sender encrypts the data using the recipient’s public key.
4. Sending: The encrypted data gets sent to the recipient.
5. Decryption: The recipient uses their private key to decrypt the message.

Public keys are crucial because they help protect sensitive information during digital communication. The public key encrypts messages, while only the recipient holds the private key for decryption. This method also supports creating digital signatures, validating the sender’s identity, and ensuring the message remains unchanged during transit.

Public key technology finds its applications mainly in:

1. Encryption: Public keys encrypt messages before sending. Since the keys are mathematically linked, only the private key can decrypt the information. This setup keeps unauthorized users from easily accessing the data.

2. Digital signatures: Here’s how it works: The sender chooses the file, calculates a hash value of the contents, encrypts that hash with their private key, and sends both the original file and the digital signature. The recipient checks the signature by decrypting the hash with the sender’s public key and comparing it to the hash of the original file. If they match, it’s good; if not, something’s awry.

3. Secure Socket Layer (SSL) and Transport Layer Security (TLS): These protocols leverage public key encryption to secure communication between a client and server, allowing for HTTPS connections. The public key is in the SSL/TLS certificate, shared publicly, while the private key stays on the server. The session begins with an asymmetric handshake to verify identities and set up a shared session key for symmetric encryption.

4. Cryptocurrencies: Public keys and digital signatures are essential here. They produce crypto addresses, establish ownership of private keys, and authorize transactions. The public key acts as a hashed version of the private key, proving the digital signature’s origin and validating transactions.

So, what’s the difference between a public key and a private key? In asymmetric cryptography, the public key encrypts data, while the private key, known only to its owner, decrypts it. You can share your public key widely, but the private key stays private.

Symmetric encryption is faster because it uses a shared key, making it efficient for many communications. However, since that key can be stolen, it’s not ideal for high-security scenarios, like banking or crypto transactions.

Public key encryption has some risks to consider:

1. Low-quality keys: A poorly constructed key can invite attacks, so it’s critical to use long, random keys.

2. Key mismanagement: Proper distribution and rotation of keys are needed to prevent theft.

3. Lost private keys: Losing the private key means losing access to the data.

4. Man-in-the-middle attacks: If a malicious party compromises a certificate or key, they can intercept sensitive data.

To mitigate these risks, use strong encryption algorithms such as RSA and periodically rotate keys. Always verify the authenticity of digital certificates before trusting any public keys.

The origins of public key encryption trace back to 1976 when Whitfield Diffie, Martin Hellman, and Ralph Merkle published a paper that laid the groundwork for what we now call public key cryptography. Their work on the Diffie-Hellman key exchange paved the way for generating keys that help secure communications between two parties. Since then, more algorithms have emerged, playing a vital role in protecting data across various applications in finance and e-commerce.