Signing and Digital Signatures

Definition

• A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software, or digital document.

Concept

1. Creation: To create a signature, signing algorithms use a one-way hash function and make use of the private key depending on the algorithm.
2. Validation: The validator can make use of its key to check if the payload’s hash and the signature’s hash matches.
   • If yes, the payload is valid and untampered with.
   • Since a private key is used for signing, it also provides non-repudiation.

Signing Algorithms

1. HS256 (HMAC with SHA-256)

• Definition: HS256 is an implementation of HMAC where the Hashing function used is SHA-256.
• Security: HMAC provides authentication and integrity.

2. RS256 (RSA Signature with SHA-256)

• Definition: An asymmetric signature algorithm.
• Security: Provides authentication, integrity, and non-repudiation.
• Steps:
  1. Create a Hash: The payload and header are hashed.
  2. Encrypt the Hash: The hash is then encrypted using the private key. This encrypted hash is the signature. (see Encryption)

• Steps for verification:
  1. Create hash of the signed content
  2. Decrypt the signature and match the created hash and the decrypted content