Public-key encryption, sometimes called public key cryptography or asymmetric cryptography, is a method of creating a secure communication channel between two connected devices. Public-key encryption enables much of the modern web infrastructure to operate safely, securely, and efficiently without sacrificing speed or performance to make it happen.
How Does Public-Key Encryption Work?
To establish an encrypted tunnel between two points, each client, user, device, or server has a unique pair of cryptographic keys generated by a specialized algorithm. This algorithm can change depending on the type of connection, the devices connecting, and the network they're connecting over.
"Keys", in this context, refer to large numbers that are mathematically linked. The public key encrypts the data, and the private key decrypts it. Consider a locked mailbox as an example. Anyone can place a letter inside the mailbox (the public key), but only a private key can open the mailbox to read the letter inside (this is the private key). Your client device is the only one with the private key, and though anyone could theoretically take the mailbox, they won't be able to access its contents unless they have the private key.
To confirm the sender's identity, the process is reversed. The sender can use their own private key to sign a letter (to continue on the earlier metaphor), almost like using a wax seal. Anyone who receives that message can use a public key to verify the legitimacy of the wax seal, which guarantees both that the message is from the intended sender and that the message hasn't been tampered with during transit.
Here's how the process breaks down in practice:
- Preparation: The receiving client device makes its public key available to the sender.
- Encryption: The sender uses the client's public key to encrypt the message.
- Transmission: The sender transmits the encrypted message to the client.
- Decryption: The client uses their private key to decrypt the message.
Data encrypted with a public key can only be decrypted by a matching private key. This ensures the security of the communication and guarantees that no one else can gain access to the message's content.
What Is Public-Key Encryption Used For?
Public-key encryption is one of the core pillars of web security. It's used for everything from securing websites over the HTTPS protocol to securing email over PGP. Cryptocurrency uses private keys to verify the authenticity of transactions on the blockchain, while public keys are utilized to determine a public address used to receive funds.
Digital certificates use the public key infrastructure (PKI) to verify that a trusted authority has determined that a client or server is who they say they are. PKI protects against man-in-the-middle attacks that try to disguise themselves as either the sender or receiver to intercept data while in transit.
What Algorithms Does Public-Key Encryption Use?
To encrypt connections, public-key algorithms rely on a bevy of various encryption methods. These include RSA, ECC, Diffie-Hellman, and PQC.
Rivest, Shamir, Adleman (RSA)
Of the encryption methods mentioned above, RSA is one of the oldest. But that doesn't mean it's inherently less secure; in fact, it's anything but.
Based on the difficulty of factoring two large prime numbers, RSA multiplies two large prime numbers and asks both sides of the key exchange to solve for that equation. Simplistic in approach but deeply complicated to solve, RSA algorithms are efficient in their implementation but still make for a near-impenetrable wall of math that would take even the world's most powerful supercomputers trillions of years to solve on their own.
RSA is most commonly used in HTTPS, digital certificates, and digital signatures.
Elliptic Curve Cryptography (ECC)
Though less popular than RSA in today's security environment, ECC is quickly overtaking RSA as a more stable, future-proof option. ECC uses a newer mathematical approach based on the algebraic structure of elliptic curves over finite fields.
For the non-math nerds out there, this basically means they chart their solve parameters over a physical space that remains deeply difficult for linear computers to solve on an equation-by-equation basis. However, they achieve this difficulty with much smaller key sizes, which means lower loads on storage and computation for the exchanging devices.
The algorithm is favored especially in mobile and other resource-constrained environments.
Hybrid cryptosystems
Because both RSA and ECC can be computationally expensive depending on the device and necessary security levels, many protocols will operate on a hybrid approach. TLS, for example, can use both RSA and ECC to quickly exchange a temporary symmetric session key between both parties. That key is then switched to decrypt the majority of the data for faster communications.
Conclusion
In essence, public-key encryption is the quiet, mathematical magic holding our entire digital world together. It's the handshake between strangers, the sealed envelope in a sea of open postcards. It's not just a feature; it's the fundamental assumption of trust that keeps your digital life from becoming an open book. Without it, the internet as we know it simply couldn't exist!