Question 552 - CISA discussion

A digital signature is a specific type of e-signature that is backed by a digital certificate. A digital certificate is a document that contains the public key of a signer and is issued by a trusted third party called a certificate authority (CA). A digital signature provides proof of the identity of the signer and the integrity of the signed document.

A characteristic of a digital signature is that it is unique to the message. This means that a digital signature cannot be copied from one document to another without being detected as invalid. A digital signature is created by applying a mathematical function called a hashing algorithm to the document. A hashing algorithm produces a fixed-length output called a hash or digest from any input data. The hash is unique to the input data; any change in the input data will result in a different hash.

The signer then encrypts the hash with their private key (a secret key that only they know) to create the digital signature. The encrypted hash is attached to the document as the digital signature. The recipient of the document can verify the digital signature by decrypting it with the signer's public key (a key that is publicly available and matches the private key) to obtain the hash. The recipient then applies the same hashing algorithm to the document to generate another hash. The recipient then compares the two hashes; if they match, it means that the document has not been altered and that the signer is authentic.

Therefore, a digital signature is unique to the message because it is derived from the hash of the message, which is unique to the message.

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