How digital signature works

A digital signature is a cryptographic technique that ensures the integrity, authenticity, and non-repudiation of digital messages or documents. It is commonly used in electronic transactions, software distribution, and other scenarios where verification of the origin and integrity of digital content is important.

Here's a simplified explanation of how digital signatures work:

1. Key Pair Generation:

   – The signer generates a pair of cryptographic keys—a private key and a public key. These keys are mathematically related but cannot be derived from each other. The private key is kept secret, while the public key can be shared.

2. Signing:

   – To sign a document or message, the signer uses their private key to perform a mathematical operation (usually a digital signature algorithm) on a hash (digest) of the content. The hash function converts the content into a fixed-size string of characters, and any change in the content will result in a different hash.

3. Public Key Distribution:

– The signer distributes their public key to others who need to verify the digital signatures. This key is often distributed through digital certificates, which are issued by a trusted third party called a Certificate Authority (CA).

4. Verification:

   – To verify the signature, the recipient uses the public key of the signer to decrypt the digital signature. This process involves performing a mathematical operation on the signature, and the result should match the hash of the original content.

5. Hash Comparison:

   – The recipient independently computes the hash of the received content. If the decrypted signature matches the computed hash, the content is considered authentic and has not been altered since the signature was created.

6. Non-Repudiation:

   – Since the private key is known only to the signer, successful verification provides evidence that the signer, and no one else, generated the digital signature. This property is known as non-repudiation and is crucial in legal and business contexts.

In summary, digital signatures use a pair of keys (private and public) to sign and verify the integrity and origin of digital content. The private key is used to create the signature, and the public key is used to verify it. This ensures that the content has not been tampered with and comes from the claimed sender.