What is Rivest-Shamir-Adleman (RSA)?

What is Rivest-Shamir-Adleman?

RSA, short for Rivest-Shamir-Adleman, is one of the most recognized encryption algorithms in cybersecurity.

It introduced the idea of asymmetric encryption—where one key locks the data and a different key unlocks it. RSA is trusted across industries to keep data confidential, verify identities, and protect systems that can’t afford to be compromised.

It’s a cornerstone of digital security, and though it’s been around since the 1970s, it’s still hard at work behind the scenes in many of the tools and services you rely on every day.

How Rivest-Shamir-Adleman encryption works

RSA works by pairing a public key (which anyone can use to encrypt information) with a private key (which only the owner can use to decrypt it).

Here’s the short version:

• Two large prime numbers are chosen at random
• They’re multiplied together to create a number that’s tough to reverse-engineer
• That number becomes part of the key pair

Anyone can use the public key to scramble a message. But without the private key, unscrambling it isn’t practical—even with massive computing power.

Rivest-Shamir-Adleman also works in reverse. When used for digital signatures, a private key signs the data, and a public key verifies it. That’s how we prove that files or messages came from a trusted source.

Where you’ll find RSA in use

RSA shows up in more places than you might think.

It’s used to:

• Secure web traffic via TLS/HTTPS
• Authenticate users and devices with digital certificates
• Protect emails and attachments
• Support multi-factor authentication workflows
• Safeguard software licensing
• Encrypt sensitive financial transactions

In most cases, RSA handles the secure exchange of keys, which are then used by faster symmetric encryption methods to handle the heavy lifting.

Why RSA is still trusted

RSA holds its ground because of one core idea: factoring large numbers is hard. That challenge is what keeps attackers from easily uncovering private keys.

The algorithm is strongest when used with long key sizes—2048-bit or 4096-bit being the current standards. Modern implementations also apply padding techniques like OAEP to further reduce the risk of known attacks.

RSA doesn’t rely on secrecy—it’s published, well-vetted, and battle-tested. But like any cryptographic tool, its strength depends on how it’s deployed.

Weak points and what to watch for

RSA is powerful, but it’s not invincible:

• Weak key generation: If the random numbers used are predictable, keys can be broken.
• Side-channel attacks: Attackers can use hardware behavior (like timing or power consumption) to infer secrets.
• Outdated key lengths: 1024-bit keys are no longer safe and should be retired.
• Quantum computing risk: RSA could be broken by future quantum machines using Shor’s algorithm.

Security teams are already evaluating alternatives in preparation for a post-quantum world. But today, RSA remains reliable—especially when implemented with care.

What good RSA looks like

To use Rivest-Shamir-Adleman effectively:

• Stick with strong, well-tested key lengths (2048 bits or higher)
• Use cryptographic libraries that support padding schemes like Optimal Asymmetric Encryption Padding (OAEP)
• Store private keys in tamper-resistant hardware
• Regularly monitor for new vulnerabilities
• Stay informed about evolving standards and quantum-safe options

RSA may be a legacy algorithm, but it’s still a workhorse. And when done right, it’s an asset you can trust to support secure communications across your business.

More resources

Blogs:

Transitioning to Quantum-Safe Encryption

How does encryption work? A look at symmetric and asymmetric encryption