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Beginner Topic 17 of 51 Security & Cryptography

Hash Functions

Functions mapping data to fixed-size fingerprints.

How it works

A cryptographic hash function maps input of any size to a fixed-size digest and is designed to be one-way, so it is infeasible to find an input for a given hash, to find a second input with the same hash and to find any two inputs that collide. A tiny change in the input changes the output completely, the avalanche effect. Hashes are deterministic and fast, and they underpin integrity checks, signatures and many protocols.

Where it is used

File checksums, software download verification, digital signatures, Git object identifiers, blockchains, deduplication and password-hashing constructions use hash functions.

Common pitfall

Broken functions such as MD5 and SHA-1 should not be used for security because collisions can be created. Hashes are not encryption and cannot be reversed, but short or guessable inputs can be brute-forced. A plain hash does not authenticate the sender; use an HMAC. For passwords, use slow dedicated algorithms.

Where it fits in the course

Hash Functions is topic 17 of 51 in Security & Cryptography, rated Beginner. It follows RSA. The next topic is SHA Family.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Security & Cryptography quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Hash Functions?
Functions mapping data to fixed-size fingerprints. It belongs to Security & Cryptography and is a beginner-level topic.
Where do people use Hash Functions?
File checksums, software download verification, digital signatures, Git object identifiers, blockchains, deduplication and password-hashing constructions use hash functions.
What is the most common mistake with Hash Functions?
Broken functions such as MD5 and SHA-1 should not be used for security because collisions can be created.
What should I learn before this topic?
Start with RSA, the topic just before it in Security & Cryptography.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Security & Cryptography quiz. You can also explore Hash Table in the Visual Lab.
Is Hash Functions hard to learn?
It is a Beginner topic, so it works as an entry point. If the terms are new, read the explanation twice and try the visualizer before the quiz.
How long does it take to learn Hash Functions?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Hash Functions?
RSA, SHA Family, Asymmetric Encryption are closely connected. The full list is in the related topics section of this page.
What should I study after Hash Functions?
Continue with SHA Family, the next topic in Security & Cryptography.

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