Hashing algorithms (SHA, MD5) in Cybersecurity - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Hash Function Output Lengths

Which of the following correctly describes the output length of the MD5 and SHA-256 hashing algorithms?

A MD5 produces a 128-bit hash, while SHA-256 produces a 256-bit hash.

B MD5 produces a 256-bit hash, while SHA-256 produces a 128-bit hash.

C Both MD5 and SHA-256 produce 256-bit hashes.

D Both MD5 and SHA-256 produce 128-bit hashes.

💡 Hint

Think about the number in the SHA-256 name and the standard output size of MD5.

MD5 outputs a 128-bit (16-byte) hash. SHA-256 outputs a 256-bit (32-byte) hash, which is twice as long, providing stronger security.

📋 Factual

intermediate

Collision Resistance in Hashing

Which statement best explains the concept of collision resistance in hashing algorithms like SHA and MD5?

A It means it is impossible for two different inputs to produce the same hash output.

B It means it is computationally infeasible to find two different inputs that produce the same hash output.

C It means the hash output is always unique for every input without exception.

D It means the hash function can be reversed to find the original input.

💡 Hint

Consider what 'computationally infeasible' means compared to 'impossible'.

Collision resistance means that while collisions can theoretically exist, it is extremely hard to find two different inputs with the same hash output using current computing power.

🔍 Analysis

advanced

Security Risks of MD5

Given that MD5 is widely considered insecure today, what is the main reason for this status?

A MD5 is vulnerable to collision attacks, allowing attackers to create different inputs with the same hash.

B MD5 hashes can be easily reversed to reveal the original input.

C MD5 hashes are too long, making them inefficient for modern systems.

D MD5 uses outdated encryption keys that can be cracked with brute force.

💡 Hint

Think about what collision attacks mean for hash security.

MD5 is vulnerable to collision attacks, meaning attackers can find two different inputs that produce the same hash, undermining its reliability for security.

❓ Comparison

advanced

Comparing SHA-1 and SHA-256

Which of the following correctly compares SHA-1 and SHA-256 in terms of security and output size?

A SHA-1 produces a 256-bit hash and is less secure than SHA-256 which produces a 160-bit hash.

B SHA-1 produces a 160-bit hash and is more secure than SHA-256.

C SHA-1 and SHA-256 both produce 256-bit hashes but SHA-1 is faster.

D SHA-1 produces a 160-bit hash but is less secure than SHA-256, which produces a 256-bit hash.

💡 Hint

Recall the bit lengths and known vulnerabilities of SHA-1.

SHA-1 outputs 160 bits but has known vulnerabilities making it less secure. SHA-256 outputs 256 bits and is currently considered secure.

❓ Reasoning

expert

Choosing a Hashing Algorithm for Password Storage

You need to store user passwords securely in a database. Which hashing algorithm choice is best and why?

A Use SHA-256 because it is more secure than MD5 and widely used.

B Use SHA-1 because it balances speed and security well.

C Use a specialized password hashing algorithm like bcrypt or Argon2 instead of MD5 or SHA variants.

D Use MD5 because it is fast and widely supported.

💡 Hint

Think about what makes password hashing different from general hashing.

MD5, SHA-1, and SHA-256 are general-purpose hashes and are fast, which makes them vulnerable to brute-force attacks. Specialized algorithms like bcrypt or Argon2 are designed to be slow and include features like salting, making them better for password storage.

Practice

1. What is the primary purpose of hashing algorithms like MD5 and SHA in cybersecurity?

easy

A. To compress files to save storage space

B. To create a fixed-size code representing data for integrity verification

C. To encrypt data so only authorized users can read it

D. To generate random passwords automatically

Solution

1. Step 1: Understand hashing function role

   Hashing algorithms convert any input data into a fixed-size string of characters, called a hash, which uniquely represents the original data.

2. Step 2: Identify the main use in cybersecurity

   This fixed-size hash is mainly used to verify data integrity, ensuring data has not been altered.

3. Final Answer:

   To create a fixed-size code representing data for integrity verification -> Option B

4. Quick Check:

   Hashing = Data integrity check [OK]

Hint: Hashing creates unique codes to check data changes [OK]

Common Mistakes:

• Confusing hashing with encryption
• Thinking hashing compresses data
• Believing hashing generates passwords

2. Which of the following is the correct way to represent the MD5 hash of the string "hello"?

easy

A. A variable-length string depending on input size

B. A plain text copy of the original string

C. A 256-bit binary string

D. A 128-bit fixed-length hexadecimal string

Solution

1. Step 1: Recall MD5 hash size

   MD5 produces a fixed-size hash of 128 bits, usually shown as a 32-character hexadecimal string.

2. Step 2: Compare options with MD5 output format

   The 128-bit fixed-length hexadecimal string correctly describes MD5 output as a fixed-length hexadecimal string.

3. Final Answer:

   A 128-bit fixed-length hexadecimal string -> Option D

4. Quick Check:

   MD5 hash length = 128 bits [OK]

Hint: MD5 always outputs 128-bit hex strings [OK]

Common Mistakes:

• Thinking MD5 output length varies
• Confusing MD5 with SHA-256 length
• Assuming output is plain text

3. Consider this Python code snippet using hashlib:

import hashlib
hash_object = hashlib.sha256(b'password123')
hex_dig = hash_object.hexdigest()
print(hex_dig)

What will this code output?

medium

A. A 64-character hexadecimal string representing the SHA-256 hash of 'password123'

B. The original string 'password123'

C. An error because of incorrect input type

D. A 32-character hexadecimal string representing the MD5 hash

Solution

1. Step 1: Understand hashlib usage

   The code uses hashlib.sha256 to hash the byte string b'password123'. The hexdigest() method returns the hash as a hexadecimal string.

2. Step 2: Identify output length and content

   SHA-256 produces a 256-bit hash, which is 64 hex characters long. The output will be this 64-character hex string representing the hash.

3. Final Answer:

   A 64-character hexadecimal string representing the SHA-256 hash of 'password123' -> Option A

4. Quick Check:

   SHA-256 output length = 64 hex chars [OK]

Hint: SHA-256 hashes output 64 hex characters [OK]

Common Mistakes:

• Expecting original string as output
• Confusing input type causing error
• Mixing MD5 and SHA-256 output lengths

4. A developer wrote this code to hash a password using MD5:

import hashlib
password = 'mypassword'
hash = hashlib.md5(password)
print(hash.hexdigest())

What is the error in this code?

medium

A. The print statement syntax is incorrect

B. MD5 does not have a hexdigest() method

C. The input to md5() must be bytes, not a string

D. The hashlib module does not support MD5

Solution

1. Step 1: Check input type for hashlib.md5()

   hashlib.md5() requires a bytes-like object, but the code passes a string directly.

2. Step 2: Identify correct fix

   The string should be encoded to bytes using password.encode() before passing to md5().

3. Final Answer:

   The input to md5() must be bytes, not a string -> Option C

4. Quick Check:

   hashlib.md5() input = bytes [OK]

Hint: Always encode strings to bytes before hashing [OK]

Common Mistakes:

• Passing string directly without encoding
• Thinking hexdigest() is missing
• Assuming MD5 unsupported in hashlib

5. You want to securely store user passwords. Which approach is best considering hashing algorithms?

hard

A. Use SHA-256 with a unique salt for each password

B. Use MD5 without salt because it's faster

C. Store passwords in plain text for easy retrieval

D. Use SHA-1 without salt since it's widely supported

Solution

1. Step 1: Understand password storage best practices

   Storing passwords securely requires hashing with a strong algorithm and adding a unique salt to prevent attacks like rainbow tables.

2. Step 2: Evaluate options

   SHA-256 is stronger than MD5 and SHA-1. Using a unique salt per password improves security significantly.

3. Final Answer:

   Use SHA-256 with a unique salt for each password -> Option A

4. Quick Check:

   Strong hash + salt = secure password storage [OK]

Hint: Always salt and use strong hashes like SHA-256 [OK]

Common Mistakes:

• Using MD5 without salt thinking it's secure
• Storing passwords as plain text
• Using outdated SHA-1 without salt