Understanding a Digital Signature

Posted by in CASP, CISSP, Get Certified Get Ahead, Security+, SSCP | Comments Off on Understanding a Digital Signature

If you’re studying for a security certification such as Security+ , SSCP, CISSP, or CASP, you need to have a basic understanding some
basic cryptography topics such as a digital signature. For example, you should be able answer questions like this:

“What key is used for encryption of a digital signature?”

“What key is used for decryption of a digital signature?”

In order to answer, these questions, you need to understand how a digital signature is created.

As background, a digital signature provides:

  • Authentication.
    The digital signature provides assurances that the email was sent by who it was claimed to be sent by. For example, if an
    IT manager sends an email to employees with a digital signature, these employees have assurances that the IT manager sent it. In contrast, a spear phishing email may spoof the email address of someone within the company, but without a digital signature, it’s not easy to verify the actual sender.
  • Non-repudiation.
    The sender cannot later deny sending the message. This is often done with transactions performed over the Internet. For example, if a financial customer requests the transfer of funds using a digital signature, the customer can’t later deny requesting the transfer.
  • Integrity.
    Basic hashing techniques are used to ensure the integrity of the message is not lost. The recipient has assurances that the received message is the same as the sent message.

CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide

“All you need to pass.” – Amazon Reviewer


Also, it’s important to understand the basics of asymmetric encryption in order to understand how a digital signature is created and used. When teaching these topics, I often have questions from students that are answered by repeating these points. It’s easy to get confused, but if you come back to the basics, the answers become clear. Here are a few important points on asymmetric encryption:

  • Asymmetric keys are in matched pairs of a public key and a private key
  • Anything encrypted with a public key can only be decrypted with the matching private key
  • Anything encrypted with a private key can only be decrypted with the matching public key
  • Private keys are always kept private and never shared
  • Public keys are freely shared by embedding them in a certificate

For example, here’s a public key in a certificate:

With the basics out of the way, here’s how a digital certificate is created. After drafting an email, the sender creates a digital signature, often
by just clicking a button in their email program. Here’s what happens behind the scenes:

  • The email is hashed.
    This hash ultimately provides integrity.
  • The sender’s private key is retrieved.
    Remember, only the sender has access to the sender’s private key. Only the sender can digitally sign own email.
  • The hash of the email is encrypted with the sender’s private key.
    This creates the digital signature. This encryption process does not encrypt the actual email. If encryption is desired, it’s a completely separate process.
  • The original email is sent with the digital signature.

When the recipient receives the email, the digital signature is analyzed to prove authentication, non-repudiation, and integrity. In most cases, the email program does all the work without any user interaction. However, here’s what happens behind the scenes:

  • The recipient retrieves the sender’s public key.
    The public key is retrieved from the sender’s certificate. The sender may have sent the certificate to the recipient previously, or it may be accessible on a network.
  • The recipient decrypts the encrypted hash with the sender’s public key.
    If this is successful, it must have been encrypted with the sender’s private key. This provides non-repudiation and authentication, and also shows the original hash of the sent message. If it fails, it proves that it was not encrypted with the sender’s private key and the recipient will see an error indicating the digital signature could not be verified.
  • The received message is hashed.
    A hash is simply a fixed-length number and it will always be the same no matter how many times it’s calculated, as long as the original data I not changed.
  • The hashes are compared.
    If the decrypted hash of the sent message is the same as the hash of the received message, you know the message has not changed. This provides integrity.

That’s it. There are several steps involved in the process of creating the digital signature, and some important cryptography concepts involved, but if you plan on taking a security certification such as Security+, SSCP, CISSP, or CASP, it’s valuable to understand what a digital signature is, what it provides, and how it’s created.

This article provides a description of digital signatures and a little on asymmetric cryptography. If you want some practice test questions for the SY0-401 Security+ exam, check out this book:

CompTIA Security+: Get Certified Get Ahead- SY0-401 Practice Test Questions (Kindle Version)

CompTIA Security+: Get Certified Get Ahead- SY0-401 Practice Test Questions(Book Version)

If you’re looking for more information related to Security+ cryptography topics – check out this blog.

Master Security+ Performance Based Questions Video

Security+ Practice Test Questions

SY0-501 Practice Test Questions 

Over 300 realistic Security+ practice test questions

All questions include explanations so you'll know why the correct answers are correct,

and why the incorrect answers are incorrect.

Pass the Security+ Exam

the First Time You Take It

Multiple quiz formats to let you use these questions based on the way you learn.
  • Learn mode - randomized. View each of the questions in random order. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.
  • Learn mode - not randomized. View each of the questions in the same order. Use this if you want to make sure that you see all of the questions. Learn mode allows you to keep selecting answers until you select the correct answer. Once you select the correct answer, you'll see the explanation. Click here to see how learn mode works.
  • Test mode - randomized. View each of the questions in random order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.
  • Test mode - not randomized. View each of the questions in the same order. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.
  • Test mode - 75 random questions. View 75 random questions from the full test bank similar to how the Security+ exam has a potential maximum of 75 multiple choice questions. In test mode, you can only see the correct answers and explanations after you complete the test. Click here to see how test mode works.

Get the full bank of SY0-501 Practice Test Questions Here

 SY0-501 Practice Test Questions


INCLUDES QUESTIONS TO HELP YOU PREPARE

FOR THE NEW PERFORMANCE BASED QUESTIONS 

Bonus - Performance Based Questions

Three sets of performance-based questions including over 30 questions. These questions show you what you can expect in the live exam. They include drag and drop, matching, sorting, and fill in the blank questions. See a demo here.

Bonus - Extra Practice Test Questions

New multiple-choice questions in the extra test bank. Questions are added occasionally. You can see what has been added recently here.

Get the full bank of Security+ (SYO-501) Practice Test Questions Here

Get the full bank of Security+ Practice Test Questions

Click here if you're looking for SY0-501 Full Study Package

Security+ Full Access Package

Get Certified Get Ahead Security+

Pass the First Time!

Up-to-date Content

New multiple-choice and performance-based questions added regularly

Pass the first time with quality practice test questions, performance-based questions, flashcards, and audio.

Buy The Full Access Study Package Today

60 Days Access

Need more time? You can easily renew for another 60 days at a significantly reduced price.

All materials are available online shortly after making your payment.

Get the Security+ Full Access Study Package Here

Our online Security+ study materials are the perfect complement to the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide. They can also be used to help ensure you're ready no matter what study guide you're using.

This exam is expensive.

Make sure you're ready before exam day. 

Here's what you'll get:
  • All of the multiple-choice questions from the best-selling CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide. See a demo here. All questions have full explanations so you'll know why the correct answers are correct and why the incorrect answers are incorrect.
  • Over 40 new multiple-choice questions we've added after publishing the study guide.
  • Over 30 performance-based questions. See a demo here.
  • All of the flashcards from the study guide. View them in any Web browser.
  • All of the audio from the study guide. Listen to a sample here.
  • Access to a free discount code for 10% off your Security+ voucher.

Buy The Full Access Study Package Today

60 Days Access

All materials are available online shortly after making your payment.

Get the Security+ Full Access Study Package Here

Security+ Full Access Package

Get Certified Get Ahead Security+

Pass the First Time!

Up-to-date Content

New multiple-choice and performance-based questions added regularly

Pass the first time with quality practice test questions, performance-based questions, flashcards, and audio.

Buy The Full Access Study Package Today

60 Days Access

Need more time? You can easily renew for another 60 days at a significantly reduced price.

All materials are available online shortly after making your payment.

Get the Security+ Full Access Study Package Here

Our online Security+ study materials are the perfect complement to the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide. They can also be used to help ensure you're ready no matter what study guide you're using.

This exam is expensive.

Make sure you're ready before exam day. 

Here's what you'll get:
  • All of the multiple-choice questions from the best-selling CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide. See a demo here. All questions have full explanations so you'll know why the correct answers are correct and why the incorrect answers are incorrect.
  • Over 40 new multiple-choice questions we've added after publishing the study guide.
  • Over 30 performance-based questions. See a demo here.
  • All of the flashcards from the study guide. View them in any Web browser.
  • All of the audio from the study guide. Listen to a sample here.
  • Access to a free discount code for 10% off your Security+ voucher.

Buy The Full Access Study Package Today

60 Days Access

All materials are available online shortly after making your payment.

Get the Security+ Full Access Study Package Here

CompTIA Security+ Get Certified Get Ahead: SY0-501 Study Guide

Subscribe To Our Newsletter

Join our mailing list and get a free excerpt of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide.  This excerpt includes the introduction and Chapter 1. 

You have Successfully Subscribed!

Get Certified Get Ahead is a participant in the Amazon Services LLC Associates Program,
an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.

Copyright © 2015 Get Certified Get Ahead. All Rights Reserved.