Now when a document is electronically signed, the signature is created by using the signer’s private key, which of course is kept securely in place by the signer. This is now where the mathematical algorithm comes in. It will act as a cypher and create data to match the signed document. This process is known as a “hash” and will encrypt the data. The result is that the encrypted data is now the digital signature. This signature will also show the time the document was electronically signed. At this point, if for whatever reason the document is changed, the digital signature will become automatically invalidated.

Let’s look at an example. Amanda has just signed an electronic agreement to sell her home using her private key. The buyer, Nicholas, now receives the document. Nicholas also received the public key that came with the document. If this public key cannot validate the signature (using the cypher created by the keys), it means that this signature is either not Amanda’s or that the document was changed since it was signed. Her signature is now considered invalid.

When we talk about the integrity of a digital eSignature, we need to discuss how PKI’s requirement is that the keys need to be created, used, and saved all in a secure form. This manner of security normally requires the use of a reliable Certificate Authority (CA). RSA is one company, for example, that provides secure certification.