A digital signature system that uses asymmetric cryptography is a complex task that requires a deep understanding of the underlying technology. Here are the steps that you can follow to create such a system:
Choose a public-key cryptographic algorithm: Asymmetric cryptography relies on a public-key cryptographic algorithm to generate a pair of keys: a public key and a private key. There are several algorithms that you can choose from, such as RSA, DSA, and ECC.
Generate a key pair: Using the chosen algorithm, generate a pair of keys: a private key and a corresponding public key. The private key should be kept secret and secure, while the public key can be shared with anyone.
Hash the document: To ensure the integrity of the document, compute a hash of the document using a cryptographic hash function, such as SHA-256.
Sign the hash: Using the private key, sign the hash of the document. This creates a digital signature that is unique to the document and the private key.
Attach the signature: Attach the digital signature to the document in a way that ensures it cannot be tampered with or removed. For example, you can embed the signature in the document, or attach it as a separate file.
Verify the signature: To verify the authenticity and integrity of the document, compute the hash of the document again, and then use the public key to verify the signature. If the computed hash matches the hash in the signature, and the signature is valid, then the document has not been tampered with since it was signed, and the signature is authentic.
Store the keys securely: Store the private key securely, and ensure that only authorized users have access to it. The public key can be shared freely, as it is used for verification purposes only.
Implement the system: Finally, implement the digital signature system into your application or infrastructure, making sure to follow best practices for security and usability.