Hash Functions

5 minutes 5 Questions

Hash functions are cryptographic algorithms that take an input data of arbitrary length and produce a fixed-size output, known as a hash. The output is designed to be unique for each unique input, making it nearly impossible to reverse-engineer the input from the hash value. Hash functions are widely used for verifying data integrity, creating digital signatures, and creating unique identifiers for sensitive information. Common features of hash functions include collision resistance (it's hard to find two different inputs producing the same output), preimage resistance (given a hash, it's difficult to find the original input), and second preimage resistance (given an input, it's hard to find another input with the same hash). Popular hash algorithms include Secure Hash Algorithm (SHA) family and Message Digest (MD) family.

Guide: Understanding Hash Functions

Hash functions are an essential part of Cryptography, highly relevant for CISSP aspirants.
Why is it important: Hash functions are used to ensure data integrity. They verify the legitimacy of the data and prevent unauthorized alteration. Understanding these is vital for CISSP aspirants because it is not only about understanding how cryptography works, but also about how to protect sensitive data.
What it is: Hash Functions are mathematical algorithms that take input data and convert it into a fixed-size string of bytes. The output is unique to the input data - even a small change in the input will drastically change the output.
How it works: Hash functions work by processing the input data in blocks, using a specific mathematical function. The output, known as a hash value or checksum, is unique to each unique input.
Exam tips: The way to approach questions about hash functions in CISSP exam is to remember:
1. The hash value changes drastically with even a small modification in input.
2. Hash functions do not provide secrecy, they provide data integrity.
3. Hash functions are one way - you can't derive the original input from its hash value.
Understanding these points will help answer most questions about hash functions in the exam.

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Question 1

Alice needs to send a file to Bob and wants to confirm the file wasn't altered in transit. Which hash function would provide a secure verification method?

MD5 SHA-256 SHA-1 MD4

Correct Answer: SHA-256

SHA-256 is a strong cryptographic hash function that produces a 256-bit digest, making it a secure choice for file verification. MD4, MD5, and SHA-0 have known vulnerabilities. SHA-1 is deprecated due to potential vulnerabilities. CRC32 is not a cryptographic hash function.

Question 2

After a cyber-attack, Mike needs to determine whether the log files have been tampered with. Which hash function can provide a strong integrity check?

SHA-1 MD5 SHA-256 CRC32

Correct Answer: SHA-256

SHA-256 is a secure hash function providing strong integrity checks. MD5 and SHA-1 are considered insecure due to known vulnerabilities. CRC32 is an error-detecting code and not a hash function. BASE64 is an encoding scheme, and DES is an encryption algorithm.

Question 3

Helen needs to securely share a PDF file with her colleague. How can she verify the file integrity after transmission?

Encrypt the file using symmetric-key encryption Encode the file as a BASE64 string Generate and share a secure hash and compare it with the hash of the received file Compress the file with password protection

Correct Answer: Generate and share a secure hash and compare it with the hash of the received file

Generating and sharing a secure hash of the file allows the recipient to verify the integrity after transmission by comparing the hashes. Encryption, compression, and encoding don't directly ensure integrity. Sending multiple copies or using secure protocols doesn't guarantee file integrity.

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