What RSA is
RSA is a widely used public-key cryptography system, named after the initials of the three people who described it. It allows information to be encrypted and decrypted using a pair of keys: a public key that can be shared openly, and a private key that is kept secret. RSA is one of the earliest and most well-known public-key systems, and it underpins much secure communication.
Public and private keys
The central idea of RSA is the use of two mathematically related keys. The public key can be given to anyone and is used to encrypt a message, while the private key is kept secret and is used to decrypt it. Because only the holder of the private key can decrypt what was encrypted with the matching public key, information can be sent securely without first sharing a secret.
How RSA is used
RSA can be used to encrypt information so that only the intended recipient can read it, and it is also used to create and verify digital signatures. For encryption, a sender uses the recipient's public key, and the recipient decrypts with their private key. This ability to communicate securely without a shared secret key is what makes public-key systems like RSA so useful.
Why RSA is secure
The security of RSA rests on a mathematical problem that is very hard to solve: while it is easy to multiply two large numbers, it is extremely difficult to reverse the process and find the original numbers from the result. RSA is built so that breaking it would require solving this hard problem, which is impractical for suitably large keys, keeping the encrypted information safe.
RSA in practice
RSA has been used for decades to secure communication, such as protecting data sent over the internet and verifying identities through digital signatures. It is often used alongside other methods, for example to securely exchange a key that is then used with a faster encryption method. Its long history and solid foundations have made RSA a cornerstone of modern cryptography.
Why it matters
RSA is a foundational public-key cryptosystem that helped make secure communication over open networks possible. Understanding what RSA is - a system using a public key to encrypt and a private key to decrypt, based on hard math - clarifies a key building block of online security. For anyone interested in cryptography, it is an essential concept.
Related on Skillo
See also: What is public-key cryptography? Explained, What is symmetric vs asymmetric encryption?.
Sources
Published date reflects the original event date (2024-07-23). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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