Corbado utilizes JWTs (JSON Web Tokens) for its short-term sessions.

Every JWT has a signature to ensure that its payload remains unchanged. There are several algorithms available for creating the signature, with HS256 and RS256 being the most popular ones.

HS256 (HMAC with SHA-256) is a symmetric keyed hashing algorithm that employs a single secret key for both generating and validating the signature. This secret key must be shared between you as the developer and Corbado.

RS256 (RSA Signature with SHA-256), on the other hand, is an asymmetric algorithm that employs a public/private key pair. The private key is used to generate the signature, while the public key is used for validation. As a developer, you receive the public key, while Corbado retains the private key.

Corbado exclusively uses RS256 due to its significant advantage: only Corbado possesses the private key, making it impossible for anyone else to generate signatures or JWTs. In contrast, if HS256 were used and an ex-employee gained access to the shared secret, they could generate JWTs and log into your server as any user they desired.

As an additional security measure, Corbado periodically rotates the private keys at fixed intervals. Existing logged in users are not logged out on private key rotation.