If you’re planning on taking the Security+ exam, you should have a basic understanding of hashing algorithms and how it verifies integrity. For example, can you answer this question?
Q. Of the following choices, what can you use to verify data integrity?
A. AES
B. DES
C. RC4
D. SHA
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.
Providing Integrity with Hashing
You can verify integrity with hashing. Hashing is an algorithm performed on data such as a file or message to produce a number called a hash (sometimes called a checksum). The hash is used to verify that data is not modified, tampered with, or corrupted. In other words, you can verify the data has maintained integrity.
A key point about a hash is that no matter how many times you execute the hashing algorithm against the data, the hash will always be the same as long as the data is the same.
Hashes are created at least twice so that they can be compared. For example, imagine a software company is releasing a patch for an application that customers can download. They can calculate the hash of the patch and post both a link to the patch file and the hash on the company site. They might list it as:
- Patch file.zip
- MD5 checksum. 9d2cf3770edbb49461788164af2331f3
The Message Digest 5 (MD5) checksum is the calculated hash displayed in hexadecimal. Customers can download the hash and then calculate the hash on the downloaded file. If the calculated hash is the same as the hash posted on the web site, it verifies the file has retained integrity. In other words, the file has not changed.
Remember this
Hashing verifies integrity for data such as email, downloaded files, and files stored on a disk. A hash is a number created with a hashing algorithm, and is sometimes listed as a checksum.
MD5
Message Digest 5 (MD5) is a common hashing algorithm that produces a 128-bit hash. Hashes are commonly shown in hexadecimal format instead of a stream of 1s and 0s. For example, the MD5 hash for the patch file (listed as the MD5 checksum) is displayed as 32 hexadecimal characters instead of 128 bits. Hexadecimal characters are composed of four bits and use the numbers 0 through 9 and the characters a through f.
Many applications use MD5 to verify the integrity of files. This includes email, files stored on disks, files downloaded from the Internet, executable files, and more. The “Hashing Files” section shows how you can manually calculate hashes.
The 601 Version of the Study Guide
The CompTIA Security+: Get Certified Get Ahead: SY0-601 Study GuideEach 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 SY0-601 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.
SHA
Secure Hash Algorithm (SHA) is another hashing algorithm. There are several variations of SHA grouped into four families: SHA-0, SHA-1, SHA-2, and SHA-3:
- SHA-0 is not used.
- SHA-1 is an updated version that creates 160-bit hashes. This is similar to the MD5 hash except that it creates 160-bit hashes instead of 128-bit hashes.
- SHA-2 improved SHA-1 to overcome potential weaknesses. It includes four versions: SHA-224, SHA-256, SHA-384, and SHA-512. The numbers represent the number of bits in the hash. For example, SHA-256 creates 256-bit hashes.
- SHA-3 uses a different method than SHA-2 and can be used instead. It includes multiple versions with hashes of 224 bits, 256 bits, 384 bits, and 512 bits.
Just as MD5 is used to verify the integrity of files, SHA also verifies file integrity. As an example, it’s rare for executable files to be modified. However, some malware modifies executable files by adding malicious code into the file. Rootkits will often modify system-level files.
Some host-based intrusion detection system (HIDS) and antivirus software capture hashes of files on a system when they first scan it and include valid hashes of system files in signature definition files. When they scan a system again, they can capture hashes of executable and system files and compare them with known good hashes. If the hashes are different for an executable or system file, it indicates the file has been modified, and it may have been modified by malware.
Q. Of the following choices, what can you use to verify data integrity?
A. AES
B. DES
C. RC4
D. SHA
Answer is D. Secure Hash Algorithm (SHA) is one of many available hashing algorithms used to verify data integrity. None of the other options are hashing algorithms.
Advanced Encryption Standard (AES), Data Encryption Standard (DES), and Rivest Cipher 4 (RC4) are symmetric encryption algorithms.
You might like to view the blog post about Creating and Comparing Hashes.
