RSA Encryption Algorithm: How It Protects Your Data When You Buy Online

What is the RSA encryption algorithm? In simple terms

The RSA encryption algorithm is an asymmetric cryptosystem that allows two parties to exchange secret data without ever meeting or knowing each other. It protects your passwords, bank transfers, electronic signatures, and even your WhatsApp messages.

It’s like you wanted to send a letter to a friend but didn’t trust the post office.
You give them an open lock—one that can be closed but not opened. They put the letter in a box, lock it with your lock, and send it back. Now, even if the letter is intercepted, no one will be able to read it. Because only you can open it—you have the private key.

This is asymmetric encryption—the keys are different. Unlike symmetric encryption (where one key is used for both encryption and decryption), here the public key can be shared with everyone, while the private key is kept secret.

The algorithm is named after the three mathematicians—Rivest, Shamir, and Adleman—who introduced it in 1977. Since then, it has become the basis for HTTPS, SSL, PGP, SSH, and thousands of other systems you use every day.

How does the RSA algorithm work? No math, just logic.

Yes, RSA is built on complex number theory. But you don’t need to understand modular arithmetic to understand how it works.
Here’s a simple diagram.

• First, two keys are generated.
• Two large prime numbers are chosen, say p and q.
• In practice, these are numbers with 600+ digits.
• They are multiplied: n = p × q. This number becomes the basis of both keys.
• Based on this, two more numbers are calculated: e and d.

A public key is a pair (e, n). It can be shown to everyone.

The private key is a pair (d, n). It is kept secret.

When you submit data—for example, a card number—the system:

• Converts it to a number;
• Raises it to the power e modulo n;
• The result is an encrypted code.

The server takes this code, raises it to the power d modulo n, and gets the original number.

Why does this work?

Because it’s mathematically easy to multiply two numbers together, but it’s impossible to quickly factor the result back into its factors if they’re large enough. It’s like finding that 17 × 11 = 187—easy. Now try guessing which two prime numbers yielded 187—harder. And what if the number is 2048 bits long? Then even a supercomputer would need thousands of years.

Where we meet RSA every day

Do you think RSA is just something for programmers? No. It works behind the scenes—and you encounter it dozens of times a day.

Every time you visit a website with https://, your browser and server use RSA. The server sends the public key via an SSL certificate. The browser encrypts a temporary session key and sends it. After this, all traffic is encrypted quickly, but the key for it was transmitted via RSA.

Without RSA, HTTPS wouldn’t exist. You wouldn’t be able to securely log into a bank, buy tickets, or even access your email.

When you download a Windows or Telegram update, and the system says, “Signature valid,” it’s RSA. The developer signed the file with their private key. Your computer verified the signature with their public key and confirmed that the file hasn’t been tampered with.

Signing contracts through government services? Transfers to Sber or Tinkoff? Cryptocurrency wallets? All of this is RSA.

Important: RSA doesn’t encrypt the entire file. It only transmits the key. AES does the main encryption—it’s faster. RSA is the key to the door. After that, the fast lane begins.

Why RSA Can Be Hacked—and How to Prevent It

RSA is secure, but only if used correctly. Three main flaws make it vulnerable:

1. Short keys.
   A 512-bit key is like a child’s toy lock. It was cracked back in 1999. A 1024-bit key is considered insecure. The minimum standard today is 2048 bits. For financial systems and government contracts, 3072 or 4096 bits are recommended. If you’re a user, make sure the websites where you enter data use 2048+ bits. If you’re a developer, never use keys shorter than 2048 bits.

2. A weak random number generator.
   RSA requires truly random prime numbers. If the generator is predictable, an attacker can guess p and q. In 2008, a bug in Debian OpenSSL resulted in hundreds of thousands of SSL certificates being generated with identical numbers. They were easily cracked. The solution is to use trusted libraries and high-entropy systems, such as /dev/urandom on Linux.
3. No padding.
   If you encrypt a “bare” message, you can guess the patterns. Two identical card numbers will yield the same cipher. The solution is OAEP. This is a scheme that adds randomness. Modern libraries do this automatically—just leave it enabled.

The Future of RSA: The Quantum Challenge

Yes, RSA isn’t perfect. The main threat is quantum computers. Shor’s algorithm, running on a quantum computer, can factorize large numbers in hours instead of thousands of years. This means RSA-2048 will become vulnerable.

Such computers don’t exist yet. But the “build now, decrypt later” attack already exists. Hackers can intercept your encrypted data today and decrypt it in 10 years, when quantum computers are available.

What do professionals do?

NIST has already standardized the first post-quantum algorithms: CRYSTALS-Kyber and Dilithium. Companies are switching to hybrid schemes: RSA + the new algorithm. Banks and government agencies are already testing the transition.

But RSA isn’t going away tomorrow. It’s installed in millions of devices, from smartphones to banking terminals. It works in legacy systems that haven’t been updated in decades. RSA remains the most secure key exchange method for classic computers.

RSA isn’t obsolete. It’s just no longer the only option. It remains secure for most tasks. For long-term projects, it’s worth preparing for the transition.

RSA vs. ECC: Why Elliptic Curves Are Becoming More of a Choice

We mentioned that RSA is slow. That’s why more and more systems are switching to ECC—elliptic curve cryptography.

ECC provides the same security as RSA-2048, but with a key 10 times shorter.
256 bits versus 2048. This is important for mobile devices, IoT sensors, and blockchain. However, ECC is less common. If you’re not a developer, this isn’t your problem. Your browser and bank will choose the best option.

How to check that RSA is working correctly on a website

Just open any website with https://—for example, your bank or store. Look for the lock icon in the address bar. If it says “2048 bits” or higher, everything is fine. If it says “1024 bits,” the site uses an outdated standard. Such sites may be less secure, and it’s best not to enter sensitive data there.

You might see information like “Certificate is valid” or “Encryption: 2048-bit.” If it says “2048-bit” or higher, everything is fine. If it says “1024-bit,” the site is outdated. Such sites can be dangerous.

For those who want to check the reliability of their resource, SSL Labs is a free service that will tell you how secure your site is in just a few seconds.

RSA is not about mathematics; it’s about freedom

The RSA encryption algorithm isn’t just a formula. It’s the result of the efforts of three mathematicians—Rivest, Shamir, and Adleman—who wanted you to be able to live in the digital world without fearing for your data.

But while it works, you can:
– pay for purchases online;
– write confidential letters;
– trust digital signatures.

If you’re not a developer, you don’t need to know how it works. But you should know: without the right RSA, your security is an illusion. Check your certificates. Don’t ignore browser warnings. Keep up with updates. Because security isn’t about technology. It’s about making informed choices.

Briefly about the RSA algorithm

The RSA encryption algorithm is an asymmetric system where data is encrypted with a public key and decrypted with a private key.

It works behind the scenes in HTTPS, digital signatures, and banking.
It’s secure when used with a 2048-4096-bit key and proper padding (OAEP).

Its main threat is quantum computers, but they haven’t been created yet.
RSA isn’t the only option right now, but it’s still one of the most reliable.

To protect yourself, make sure that the sites where you enter data use 2048-bit keys.

RSA isn’t about math. It’s about your ability to live securely in the digital world.