RS256

RS256 is a signing algorithm defined by the JOSE (JSON Object Signing and Encryption) family, representing RSASSA-PKCS1-v1_5 with SHA-256. In practice, RS256 is used to create and verify digital signatures for data such as JSON Web Tokens (JWTs). The algorithm uses an asymmetric key pair: a private key to sign and a corresponding public key to verify. The algorithm identifier RS256 appears in the JOSE header as the algorithm value.

How it works: The signer hashes the message with SHA-256, then signs the hash with RSA using PKCS #1 v1.5 padding. The resulting signature can be attached to a JWT as the JWS signature. Verification uses the signer's public key and the same hashing algorithm; if the RSA signature matches, the token is considered authentic and untampered. Typical key sizes recommended are 2048 bits or larger, and keys should be protected and rotated periodically. Interoperability with PEM or JWK representations of public keys is common, enabling distribution and rotation in authentication ecosystems.

Usage: RS256 is widely used in OAuth 2.0 and OpenID Connect for securing tokens, as well as for general data integrity in JOSE-based protocols. It interoperates with standard libraries that implement RSA PKCS1 v1.5 signing with SHA-256, and supports integration into systems that rely on JWTs and JWS.

Security considerations: PKCS1 v1.5 padding has known historical weaknesses in certain contexts, leading some to prefer RSASSA-PSS with SHA-256 for higher security in new designs. When using RS256, proper key management, secure key storage, correct padding implementation, and constant-time verification are important to avoid vulnerabilities. Rely on trusted libraries and secure key distribution practices to maintain security.