Security Method Using Digital Signatures

Posted by in Security+ | 0 comments

Cryptography provides two primary security methods you can use with email: digital signatures and encryption.  If you’re planning to take the Security+ exam, you should understand that these are separate processes, but you can digitally sign and encrypt the same email.

For example, can you answer this question?

Q. Lenny and Carl work in an organization that includes a PKI. Carl needs to send a digitally signed file to Lenny. What does Carl use in this process?

A. Carl’s public key

B. Carl’s private key

C. Lenny’s public key

D. Lenny’s private key

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Get Certified Get Ahead

Signing Email with Digital Signatures

Digital signatures are similar in concept to handwritten signatures on printed documents that identify individuals, but they provide more security benefits. A digital signature is an encrypted hash of a message, encrypted with the sender’s private key. If the recipient of a digitally signed email can decrypt the hash, it provides the following three security benefits:

  • Authentication. This identifies the sender of the email. Email recipients have assurances the email actually came from who it appears to be coming from. For example, if an executive digitally signs an email, recipients know it came from the executive and not from an attacker impersonating the executive.
  • Non-repudiation. The sender cannot later deny sending the message. This is sometimes required with online transactions. For example, imagine if Homer sends an order to sell stocks using a digitally signed email. If the stocks increase after his sale completes, he can’t deny the transaction.
  • Integrity. This provides assurances that the message has not been modified or corrupted. Recipients know that the message they received is the same as the sent message.

CompTIA Security+ Study Guide

The 501 Version of the Study Guide

The CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide is an update to the top-selling SY0-201, SY0-301, and SY0-401 study guides, which have helped thousands of readers pass the exam the first time they took it.  It includes the same elements readers raved about in the previous three versions.

Each of the eleven chapters presents topics in an easy to understand manner and includes real-world examples of security principles in action.

You’ll understand the important and relevant security topics for the Security+ exam, without being overloaded with unnecessary details. Additionally, each chapter includes a comprehensive review section to help you focus on what’s important.



Over 300 realistic practice test questions with in-depth explanations will help you test your comprehension and readiness for the exam. The book includes:

  • A 75 question pre-test
  • A 75 question post-test
  • Practice test questions at the end of every chapter.

Each practice test question includes a detailed explanation to help you understand the content and the reasoning behind the question. You’ll be ready to take and pass the exam the first time you take it.

If you plan to pursue any of the advanced security certifications, this guide will also help you lay a solid foundation of security knowledge. Learn this material, and you’ll be a step ahead for other exams. This SY0-501 study guide is for any IT or security professional interested in advancing in their field, and a must-read for anyone striving to master the basics of IT security.

Kindle edition also available.

Digital signatures are much easier to grasp if you understand some other cryptography concepts. As a short review, these concepts are:

  • Hashing. Digital signatures start by creating a hash of the message. A hash is simply a number created by performing an algorithm on the message.
  • Certificates. Digital signatures need certificates, and certificates include the sender’s public key.
  • Public/private keys. In a digital signature, the sender uses the sender’s private key to encrypt the hash of the message. The recipient uses the sender’s public key to decrypt the hash of the message.

The figure shows an overview of this process. In the figure, Lisa is sending a message to Bart with a digital signature. Note that the message “I passed” is not secret. If it was, Lisa would encrypt it, which is a completely separate process. The focus in this explanation is only the digital signature.

Security Method Using Digital Signatures

Digital signature process

Lisa creates her message in an email program, such as Microsoft Outlook. Once Microsoft Outlook is configured, all she has to do is click a button to digitally sign the message. Here is what happens when she clicks the button:

  1. The application hashes the message.
  2. The application retrieves Lisa’s private key and encrypts the hash using this private key.
  3. The application sends both the encrypted hash and the unencrypted message to Bart.

When Bart’s system receives the message, it verifies the digital signature using the following steps:

  1. Bart’s system retrieves Lisa’s public key, which is in Lisa’s public certificate. In some situations, Lisa may have sent Bart a copy of her certificate with her public key. In domain environments, Bart’s system can automatically retrieve Lisa’s certificate from a network location.
  2. The email application on Bart’s system decrypts the encrypted hash with Lisa’s public key.
  3. The application calculates the hash on the received message.
  4. The application compares the decrypted hash with the calculated hash.

Full Security+ Course

SY0-501 Full Security+ Course

Helping you Pass the First Time

Online access includes all of the content from the

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

  • Introduction
  • About the exam (including information on the number of questions, test duration, passing score, types of questions and more. Also includes a listing of the exam objectives)
  • 75 question pre-assessment exam
  • Mastering Security Basics (full content from Chapter 1 of the study guide including the exam topic review and 15 practice test questions)
  • Understanding Identity and Access Management (full content from Chapter 2 of the study guide including the exam topic review and 15 practice test questions)
  • Exploring Network Technologies and Tools (full content from Chapter 3 of the study guide including the exam topic review and 15 practice test questions)
  • Securing Your Network (full content from Chapter 4 of the study guide including the exam topic review and 15 practice test questions)
  • Securing Hosts and Data (full content from Chapter 5 of the study guide including the exam topic review and 15 practice test questions)
  • Comparing Threats, Vulnerabilities, and Common Attacks (full content from Chapter 6 of the study guide including the exam topic review and 15 practice test questions)
  • Protecting Against Advanced Attacks (full content from Chapter 7 of the study guide including the exam topic review and 15 practice test questions)
  • Using Risk Management Tools (full content from Chapter 8 of the study guide including the exam topic review and 15 practice test questions)
  • Implementing Controls to Protect Assets (full content from Chapter 9 of the study guide including the exam topic review and 15 practice test questions)
  • Understanding Cryptography and PKI (full content from Chapter 10 of the study guide including the exam topic review and 15 practice test questions)
  • Implementing Policies to Mitigate Risks (full content from Chapter 11 of the study guide including the exam topic review and 15 practice test questions)
  • 75 question post-assessment exam
  • Glossary

Get the SY0-501 Full Security+ Course Here


Test your readiness with these quality materials

Random 75-question tests

Random practice tests from the all of the practice test questions in the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide. All questions include explanations so you'll know why the correct answers are correct, and why the incorrect answers are incorrect.

3 sets Performance-based Questions

Three new sets of performance-based questions with a total of 30 questions. These new questions use a new testing engine that includes realistic drag and drop, matching, sorting, and fill in the blank questions.

Flashcard Set

  • 494 Online Security+ Glossary Flashcards
  • 222 Online Security+ Acronyms Flashcards
  • 223 Online Security+ Remember This Slide from the popular CompTIA Security+ Get Certified Get Ahead: SY0-501 Study Guide

Audio - SY0-501 Security+ Remember This Audio Files

Learn by Listening. Over one hour and 20 minutes of audio (MP3 downloads.)

Audio - SY0-501 Security+ Question and Answer Audio Files

Learn by Listening. Over two hours hour and 53 minutes of audio (MP3 downloads.)

Bonus #1

Audio from the end of chapter reviews from each of the chapters in the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide. Over one hour and 40 minutes of additional audio.

Bonus #2

Access to all of the online content that is available for free to anyone that purchases the CompTIA Security+ Get Certified Get Ahead: SY0-501 Study Guide. This includes labs, extra practice test questions, and supplementary materials

Bonus #3 

Access the study materials for a total of 60 days because sometimes life happens.

Get the SY0-501 Full Security+ Course Here

If the calculated hash of the received message is the same as the encrypted hash of the digital signature, it validates several important checks:

  • Authentication. Lisa sent the message. The public key can only decrypt something encrypted with the private key, and only Lisa has the private key. If the decryption succeeded, Lisa’s private key must have encrypted the hash. On the other hand, if another key was used to encrypt the hash, Lisa’s public key could not decrypt it. In this case, Bart will see an error indicating a problem with the digital signature.
  • Non-repudiation. Lisa cannot later deny sending the message. Only Lisa has her private key and if the public key decrypted the hash, the hash must have been encrypted with her private key. Non-repudiation is valuable in online transactions.
  • Integrity. Because the hash of the sent message matches the hash of the received message, the message has maintained integrity. It hasn’t been modified.

Remember this

A digital signature is an encrypted hash of a message. The sender’s private key encrypts the hash of the message to create the digital signature. The recipient decrypts the hash with the sender’s public key. If successful, it provides authentication, non-repudiation, and integrity. Authentication identifies the sender. Integrity verifies the message has not been modified. Non-repudiation prevents senders from later denying they sent an email.

At this point, you might be thinking, if we do all of this, why not just encrypt the message, too? The answer is resources. It doesn’t take much processing power to encrypt 256 bits in a SHA-256 hash. In contrast, it would take quite a bit of processing power to encrypt a lengthy email and its attachments. However, if you need to ensure confidentiality of the email, you can encrypt it.


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

Q. Lenny and Carl work in an organization that includes a PKI. Carl needs to send a digitally signed file to Lenny. What does Carl use in this process?

A. Carl’s public key

B. Carl’s private key

C. Lenny’s public key

D. Lenny’s private key

Answer is B. Carl uses his private key to digitally sign the file.

Lenny uses Carl’s public key to decrypt the digital signature.

Lenny’s keys are not used in this scenario.

See Chapter 10 of the CompTIA Security+: Get Certified Get Ahead: SY0-401 Study Guide for more information cryptographic protocols.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

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.