Encrypting & Decrypting Email

Posted by in Security+ | 0 comments

If you’re planning to take the SY0-501 version of the Security+ exam, you should have a basic understanding of the basic concepts of cryptography. This includes ensuring confidentiality of email by encrypting and decrypting email contents.

For example, can you answer this question?

Q. Bart wants to send a secure email to Lisa, so he decides to encrypt it. Bart wants to ensure that Lisa can verify that he sent it. Which of the following does Lisa need to meet this requirement?

A. Bart’s public key

B. Bart’s private key

C. Lisa’s public key

D. Lisa’s private key

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

There are times when you want to ensure that email messages are only readable by authorized users. You can encrypt email and just as any other time encryption is used, encryption provides confidentiality.

Encrypting Email with Only Asymmetric Encryption

Imagine that Lisa wants to send an encrypted message to Bart. The following steps provide a simplified explanation of the process if only asymmetric encryption is used:

1. Lisa retrieves a copy of Bart’s certificate that contains his public key.
2. Lisa encrypts the email with Bart’s public key.
3. Lisa sends the encrypted email to Bart.
4. Bart decrypts the email with his private key.

This works because Bart is the only person who has access to his private key. If attackers intercepted the email, they couldn’t decrypt it without Bart’s private key. It’s important to remember that when you’re encrypting email contents, the recipient’s public key encrypts and the recipient’s private key decrypts. The sender’s keys are not involved in this process. In contrast, a digital signature only uses the sender’s keys but not the recipient’s keys.

In most cases, the public key doesn’t actually encrypt the message, but instead encrypts a symmetric key used to encrypt the email. The recipient then uses the private key to decrypt the symmetric key, and then uses the symmetric key to decrypt the email.

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.

Encrypting Email with Asymmetric and Symmetric Encryption

The previous description provides a simplistic explanation of email encryption used by some email applications. However, most email applications combine both asymmetric and symmetric encryption. You may remember from earlier in this chapter that asymmetric encryption is slow and inefficient, but symmetric encryption is very quick.

Instead of using only symmetric encryption, most email applications use asymmetric encryption to privately share a session key. They then use symmetric encryption to encrypt the data. For example, imagine that Lisa is sending Bart an encrypted message. The figure (steps 1 to 4) shows the process of encrypting the message and the symmetric key.  The next figure (steps 5 to 7) shows the process of sending the encrypted message and encrypted session key, and identifies how the recipient can decrypt the data:

1. Lisa identifies a symmetric key to encrypt her email. For this example, assume it’s a simplistic symmetric key of 53, though a symmetric algorithm like AES would use 128- bit or larger keys.
2. Lisa encrypts the email contents with the symmetric key of 53.
3. Lisa retrieves a copy of Bart’s certificate that contains his public key.
4. She uses Bart’s public key to encrypt the symmetric key of 53.
5. Lisa sends the encrypted email and the encrypted symmetric key to Bart.
6. Bart decrypts the symmetric key with his private key.
7. He then decrypts the email with the decrypted symmetric key.

Encrypting & Decrypting Email

Unauthorized users who intercept the email sent by Lisa won’t be able to read it because it’s encrypted with the symmetric key. Additionally, they can’t read the symmetric key because it’s encrypted with Bart’s public key, and only Bart’s private key can decrypt it.

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

S/MIME

Secure/Multipurpose Internet Mail Extensions (S/MIME) is one of the most popular standards used to digitally sign and encrypt email. Most email applications that support encryption and digital signatures use S/MIME standards.

S/MIME uses RSA for asymmetric encryption and AES for symmetric encryption. It can encrypt email at rest (stored on a drive) and in transit (data sent over the network). Because S/MIME uses RSA for asymmetric encryption, it requires a PKI to distribute and manage certificates.

PGP/GPG

Pretty Good Privacy (PGP) is a method used to secure email communication. It can encrypt, decrypt, and digitally sign email. Phillip Zimmerman designed PGP in 1991, and it has gone through many changes and improvements over the years. Symantec Corporation purchased it in June 2010.

OpenPGP is a PGP-based standard created to avoid any conflict with existing licensing. In other words, users have no obligation to pay licensing fees to use it. Some versions of PGP follow S/MIME standards. Other versions follow OpenPGP standards. GNU Privacy Guard (GPG) is free software that is based on the OpenPGP standard.

Each of the PGP versions uses the RSA algorithm and public and private keys for encryption and decryption. Just like S/MIME, PGP uses both asymmetric and symmetric encryption.


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. Bart wants to send a secure email to Lisa, so he decides to encrypt it. Bart wants to ensure that Lisa can verify that he sent it. Which of the following does Lisa need to meet this requirement?

A. Bart’s public key

B. Bart’s private key

C. Lisa’s public key

D. Lisa’s private key

Answer is A. Lisa would decrypt the digital signature with Bart’s public key and verify the public key is valid by querying a Certificate Authority (CA). The digital signature provides verification that Bart sent the message, non-repudiation, and integrity for the message.

Bart encrypts the digital signature with his private key, which can only be decrypted with his public key.

Lisa’s keys are not used for Bart’s digital signature, but might be used for the encryption of the email.

Although not part of this scenario, Bart would encrypt the email with Lisa’s public key and Lisa would decrypt the email with Lisa’s private key.

See Chapter 10 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide for more information on using 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.