A digital signature and a digital certificate, while both security measures, are different in the ways they are implemented and the background why they are implemented for. The technology industry loves to use acronyms and words that seem to either overlap with other similar words, or that are a slight variation on a word, but with widely different meanings. In this blog article, we will discuss the difference between digital signatures and digital certificates.

Why would you use a digital signature?

The most common concerns individuals and organisations face when dealing with digital documents are… is the person who signed the document who they claim to be? How can I verify if the signature is valid and hasn’t been forged? How do I validate if the document hasn’t been tampered with? Digital Signatures help solve this problem.

What is a digital signature?

A digital signature is a mechanism that is used to verify that a particular digital document, message or transaction is authentic. It provides a receiver the guarantee that the message was actually generated by the sender and it was not modified by a third party.

A digital signature is an electronic, encrypted stamp of authentication on digital data. The  signature confirms that the information originated from the signer and has not been altered.

Digital signatures can provide the added assurances of evidence to the origin, identity and status, as well as acknowledging informed consent by the signer. Below are some common reasons for applying a digital signature to communications:

• Authentication: Although messages may often include information about the entity sending a message, that information may not be accurate. Digital signatures can be used to authenticate the source of messages. The importance of high confidence in sender authenticity is especially obvious in a financial context.
• Integrity: In many scenarios, the sender and receiver of a message may have a need for confidence that the message has not been altered during transmission. So, if a message is digitally signed, any change in the message after signature invalidates the signature.
• Non-repudiation: Non-repudiation, or more specifically non-repudiation of origin, is an important aspect of digital signatures. By this property, an entity that has signed some information cannot at a later time deny having signed it. Similarly, access to the public key only does not enable a fraudulent party to fake a valid signature.

Digital signatures use a standard, accepted format, called Public Key Infrastructure (PKI), to provide the highest levels of security and universal acceptance. In many countries, digital signatures have the same legal significance as the more traditional forms (wet signature) of signed documents. Digital signatures are widely used for avoiding forging or tampering of important documents such as financial documents.

What is a digital certificate?

Digital certificates function similarly to identification cards such as passports and drivers’ licenses. Digital certificates are issued by recognised (government) authorities. When someone requests a certificate, the authority verifies the identity of the requester, certifies that the requester meets all requirements to receive the certificate, and then issues it. When a digital certificate is presented to others, they can verify the identity of its owner because the certificate provides the following security benefits:

• It contains personal information to help identify and trace the owner.
• It contains the information that is required to identify and contact the issuing authority.
• It is designed to be tamper-resistant and difficult to counterfeit.
• It is issued by an authority that can revoke the identification card at any time (for example, if the card is misused or stolen).
• It can be checked for revocation by contacting the issuing authority.

The use of a digital certificate to sign documents

When the signer uses a certificate to digitally sign a document, other people (known as relying parties) can trust the digital signature because they trust the CA has done their part to ensure the signer matches their digital identity.

So, technically speaking the difference between a digital signature and digital certificate is that a certificate binds a digital signature to an entity, whereas a digital signature is to ensure that a data/information remain secure from the point it was issued. In other words: digital certificates are used to verify the trustworthiness of a person (sender), while digital signatures are used to verify the trustworthiness of the data being sent.

Creating a digital signature using digital certificates (private key)

In a next series of blog articles, we will dig Deeper into the topic of PKI and digital certificates.