What Is a Digital Signature?

security

A digital signature is not the same as an electronic signature, despite the fact that the two are frequently confused. Despite the fact that both words contain the word “signature” and both refer to identity, they are two distinct processes. In the broadest sense, a digital signature is an electronic signature, but it has a different purpose and end goal.

A digital signature differs from a digital certificate in many ways (although the two work in conjunction). Not sure what we’re talking about? You’ll see what I mean in a moment. We’ll explain what a digital signature is and how it functions in this post. We’ll also go through some of the finer points of the digital signature process as a whole.

What Is a Digital Signature in Cryptography?

In a nutshell, a digital signature (also known as an advanced electronic signature or qualified electronic signature in some cases) is a key component of public key infrastructure (PKI) that enables users to identify who sent what (email, text, software application, etc.). Essentially, it’s a way for you to verify your identity to a third party and demonstrate that the object in question is genuine and unaltered.

In the context of the certification path, another example of a digital signature can be found in SSL/TLS certificates. The SSL/TLS certificate on SectigoStore.com, for example, is signed by the intermediate certificate using a digital signature, which is signed by the root certificate, so you can be sure this website was checked by Sectigo:
certificate-path
Hash functions, or what are more commonly known as hashes, operate in tandem with digital signatures. Do you know what SHA-2 and SHA-256 are? That’s right, those are two of the most popular hashing algorithms. (Don’t worry; we’ll go over hashing in greater detail later to clarify things.)

Digital Signatures Offer Assurance and Authenticity

… Hmm, that didn’t really help much, did it? Okay, let’s try this another way. There are three primary uses for digital signatures:

  • Authentication — You’re using a trusted third party such as a certificate authority (CA) to validate that you are the person you claim to be.
  • Non-repudiation — What this means is that no one can deny (repudiate) that it was, in fact, you who sent a message or published a piece of software.
  • Message integrity — This shows the recipient, email client, OS or server that the data hasn’t been tampered with in any way since it was signed. (Note: A digital signature doesn’t actually stop someone from tampering with signed data — it just indicates whether someone has or not so you can make a decision about whether to trust its integrity.)

Okay, it probably sounds like something you’d never end up using in daily activities, right? Wrong — and here’s why.

How a Digital Signature Can Be Used in Real World Applications

Are you curious about what a digital signature is and how your company would use it in the real world? Many businesses and organisations are now using digital signatures, which can surprise you. In reality, you’ve seen the results of a digital signature application if you’ve ever downloaded an app on your device that showed a pop-up with the name of the developer or manufacturer who made it.

Digital signatures can be used in a number of situations:

  • Email sender authentication
  • Document and certificate authentication
  • Software authentication

Some of the most common types of PKI digital certificates that use digital signatures include:

  • Email signing certificates (AKA personal authentication certificates, S/MIME certificates, client certificates, etc.)
  • Code signing certificates
  • SSL/TLS certificates

What Is the Digital Signature Process?

Now that we’ve gotten a better understanding of what a digital signature is and what it does at a high level, it’s time to get down to business and learn how it operates on a more technical level.

Since it requires the use of a collection of mathematically related public and private keys, the digital signature process is based on asymmetric cryptography.

In a nutshell, hashing is a basic method of creating a code that identifies a file uniquely. When the file is modified, the hash value is modified as well. For all intents and purposes, a hash is a one-way feature that can be applied to any length of data to generate a specific string of text (known as a hash value, digest, or fingerprint) of a fixed length.

The message creator’s private key is used to encrypt this hash digest (and the creator’s public key is used to decode it on the end user’s side). A hash’s function is to act as a checksum, ensuring that the message, code, or whatever else has been hashed hasn’t been tampered with. (This is different from encryption, which is designed to be a two-way process.)

Basically, it takes your message and runs it through a hash function (such as SHA-256) to create a hash value that looks like this:

HELLO =  ch857er1iu23rbhfiu23rhb2c2b4l8m4n

(Okay, technically, someone could reverse a hash using brute force.) However, given the amount of time and computational resources available, doing so would be pointless….)

It’s important to remember that each hash value is distinct. Collision occurs when two files produce the same hash value. A hash collision is just as bad as a car collision. In other words, the hash algorithm is ineffective and will not secure your file or post.

Anyway, imagine a hash in terms of digitally signing an email to better understand what it is. To digitally sign your account, you can use an email signing certificate. This shows your receiver that you received the message and that it hasn’t been tampered with since you pressed the “send” button. (This provides the authentication and message integrity assurance described previously.)

A Demonstration of the Digital Signature Process (for Email)

So, let’s look at how the digital signature process works in the form of sending an email:

  • Invest in an email signature certificate. A credible digital certificate provider will provide you with one (you know, like Sectigo). You must go through the authentication process and other procedures, but once you have the digital certificate, you will proceed to phase two.
  • Install your email client’s email signing certificate. Since the procedure varies from one email client to the next, we won’t tell you how to do it here. (Instructions for installing and using one of these certificates in Outlook can be found here.) But don’t worry, downloading it is just a one-time job. After that, your digital signature can be set to automatically apply to all of your outgoing messages if correctly configured.
  • You write the message you want to send. This involves the development of any text and the attachment of any additional media.
  • You apply the hash algorithm to your message (automatically). The message (and any attachments) are hashed for added protection. When digital signing is available, you don’t have to do anything because it’s automatic. (It’s done for you by your email client.)
  • You add your digital signature to the message using your email signing certificate. This transforms your email message into a pre-defined output length. It digitally signs it with your public key. This, too, occurs automatically — the email client does the heavy lifting.
  • After that, the hashed message and signature are encrypted. If you have email encryption allowed, this is the cherry on top. This is the procedure that allows you to send data over potentially unreliable transmission channels. So, even if anyone intercepts your message when it leaves your email client and moves from one email server to another, they won’t be able to read it. (However, encrypting data at rest necessitates the recipient having an email signing certificate and you having the recipient’s public key, but that’s a topic for another article.)
  • You send the encrypted and digitally signed letter. This leaves your email client and travels across the internet, from your server to theirs (and then on to their email client).
  • The digital signature is checked by your recipient using the same algorithm and your public key. Recreating your hashed digest is a part of this process.
  • The two distinct hash values are tested by the recipient’s email client. To ensure that they match, the hash value produced is compared to the one attached to your message. If they match, it means the email hasn’t been tampered with—everything is fine, and the recipient should get on with their company. If they don’t, they’ll get a warning message that there’s a problem with your email, which will put you (and your company) in a bad light. It’s not just roses.

Digital Signatures: The Last Word

As you’ve seen, digital signatures are an excellent way to establish identity and authenticate data as well as the people who created or sent it. They also collaborate to ensure the integrity of the data in question by showing whether it has been tampered with (though they can’t prevent the tampering from occurring in the first place).

Digital signatures in cryptography have a wide range of applications; they’re an important part of website, text, and email protection, among other things. Even if you aren’t aware of it, you use digital signatures every day. When you clicked to read this post, your browser used several digital signatures to verify our website.

Melina Richardson is a Cyber Security Enthusiast, Security Blogger, Technical Editor, Certified Ethical Hacker, Author at Cybers Guards & w-se. Previously, he worked as a security news reporter.