Cryptology Academy · Lesson

SHA-1 & SHA-2 Family Explained

Understand SHA-1's weakness and how SHA-256 and SHA-512 differ.

Lesson 3 of 413 steps

SHA-1 & SHA-2 Family Explained is a free Cryptology Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Cryptology Academy learning path, and your progress syncs across the web and the CoddyKit app. The Cryptology Academy course includes 4 lessons in total.

Welcome

SHA-1 and SHA-2 are the NSA-designed successors to MD5. SHA-1 is now retired. SHA-256 and SHA-512 remain the industry standard for most applications.

SHA-1 Overview

SHA-1 produces a 160-bit (20-byte) hash. Designed by NSA, published 1995. Example: SHA1('hello') = aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d

SHA-1 Structure

SHA-1 uses 80 rounds grouped in 4 stages of 20 rounds. Each stage uses different logical functions (Ch, Parity, Maj). It extends 16 input words to 80 using XOR and rotations.

SHA-1 Collision: SHAttered (2017)

In 2017, Google and CWI Amsterdam produced the first practical SHA-1 collision (the SHAttered attack). Two PDFs with identical SHA-1 hashes but different content. Cost: ~6500 GPU-years.

SHA-2 Family

SHA-2 includes: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256. All are Merkle-Damgård. SHA-256 is the most commonly used variant.

SHA-256 Structure

SHA-256 uses 64 rounds on 512-bit blocks. It maintains 8 state words of 32 bits each (a,b,c,d,e,f,g,h). Each round mixes input words using Ch, Maj, Σ0, Σ1 functions.

SHA-256 in Python

import hashlib msg = b'hello' digest = hashlib.sha256(msg).hexdigest() print(digest) # 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824

SHA-512 vs SHA-256

SHA-512 uses 80 rounds with 64-bit words, producing 512 bits. It is faster on 64-bit hardware but produces larger digests. Use SHA-512 when 256-bit security level is needed.

SHA-3 (Keccak)

SHA-3 was standardized in 2015 as an alternative design. It uses the sponge construction instead of Merkle-Damgård, making it immune to length-extension attacks.

Length-Extension Attacks on SHA-2

SHA-256(secret || message) is vulnerable: an attacker knowing Hash(message) can compute Hash(message || padding || extra). This is why HMAC uses a double-hash construction.

When to Use Which

SHA-256: general purpose, TLS, certificates, HMAC. SHA-512: higher security margin applications. SHA-3: new protocols without length-extension concerns. Never SHA-1 or MD5 for new designs.

Quick Check

What construction does SHA-3 use that makes it immune to length-extension attacks?

Answer it in the interactive lesson

Recap

You understand the SHA family evolution. Next we study the practical applications of hashes: checksums, HMAC, and Git's use of SHA.

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Frequently Asked Questions

Is the “SHA-1 & SHA-2 Family Explained” lesson free?

Yes — the full text of “SHA-1 & SHA-2 Family Explained” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Cryptology Academy course, upgrade to CoddyKit PRO. The Cryptology Academy course includes 4 lessons in total.

What will I learn in “SHA-1 & SHA-2 Family Explained”?

Understand SHA-1's weakness and how SHA-256 and SHA-512 differ. You practise Cryptology Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Cryptology Academy?

No prior experience is required. Cryptology Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “SHA-1 & SHA-2 Family Explained” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Cryptology Academy lesson?

Yes. Every Cryptology Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

What Makes a Good Hash Function
MD5: History, Uses & Why It Is Broken
SHA-1 & SHA-2 Family Explained
Hash Applications: Checksums, HMAC & Git

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