RSA Sign / Verify
Sign a message with a private key and let anyone verify it with the public key.
Never paste a real production private key into a website. This page runs entirely in your browser, but for real secrets the safest place is your own machine. Use the sample keys to learn and test.
● 🔒 Your data is processed locally in your browser with the Web Crypto API and is never uploaded to our servers.
How it works
A digital signature proves who wrote a message and that it wasn't changed. The message is hashed and the hash is signed with the private key; anyone with the public key can check it. Change a single character and verification fails. RSA-PSS uses randomized padding and is the modern choice; PKCS#1 v1.5 is still used by JWT (RS256) and many older systems.