Cryptographic Hash Functions

🚫 Still Using MD5 or SHA-1 in Digital Forensics? Here’s Why You Shouldn’t. “But it’s just a hash, what could go wrong?” When I started working in digital forensics, like most of us, I was taught to hash everything - disk images, memory dumps, even recovered files. It’s one of the core pillars of evidentiary integrity: 👉 Hash it, verify it, present it. And back then, MD5 or SHA-1 were the default go-to options. Small, fast, widely supported. But today, if you’re still relying on MD5 or SHA-1, especially for courtroom-bound evidence, you’re sitting on a ticking time bomb. 🔍 What’s the Problem? Both MD5 (Message Digest 5) and SHA-1 (Secure Hash Algorithm 1) have been cryptographically broken for years. That means: • You can intentionally create two different files with the same hash. • In court, someone could challenge your evidence with a crafted decoy file that “matches” your MD5 hash. • In malware analysis, signature collisions could allow a malicious file to sneak past defenses. 🧪 A Real Example Let’s say you’re analyzing a suspicious PDF on a seized machine. You hash the file: MD5: ee4aa52b139d925f8d8884402b0a750c But did you know that another PDF, with completely different visible content, can have exactly the same MD5 hash? This isn’t theory. It’s called a hash collision, and researchers (including Google) have done it: Two PDFs, two different messages. Same SHA-1 and MD5 hash. View: https://shattered.io Imagine standing in court, and the defense lawyer shows their version of the file - same MD5, different content. 🚨 Why This Matters in Forensics In digital forensics, hashes are treated like fingerprints, they’re meant to prove that a file hasn’t been altered. But if: • Two files can have the same fingerprint… • And you used a weak hash like MD5 or SHA-1… Then your evidence could be challenged, questioned, or dismissed. Even worse, if you’re validating disk images using MD5 hashes, and someone tampers with the image using known collision techniques, your tools might not detect it. ✅ What Should We Use Instead? 👉 Use SHA-256 or SHA-3. They’re widely supported, strong, and no known practical collisions exist as of today. Most modern forensic tools (like Autopsy, FTK, X-Ways) already support SHA-256. Just switch the default. Also: • Document which hash algorithm you used. • Hash both before and after evidence handling. • Avoid relying on a single hash - some investigators use MD5 + SHA-256 for compatibility and strength. #digitalforensics #incidentresponse

In 2001, the NSA published SHA-256. They were trying to secure classified government data. They had no idea it would eventually hold $2 trillion in digital assets. Let me tell you why this is one of the most elegant things in all of computer science. SHA stands for Secure Hash Algorithm. It takes any input, a word, a document, an entire Bitcoin block and produces a fixed 64-character output called a hash. "hello" → 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824 Change one character. The entire output changes completely. "Hello" → 185f8db32921bd46d35b5aa3b3d32e2a4a29a4e2b1b3e8f7a0c1f0b9d4e6c7a That's called the avalanche effect. And it's what makes the whole thing work. This is what actually happens when a Bitcoin transaction is verified. Every transaction gets bundled into a block. That block contains thousands of transactions, a timestamp, and a reference to the previous block. Miners take all of that data and run it through SHA-256. Twice. The output has to be below a specific target number. Something that starts with many leading zeros. Ex: 0000000000000000000abc123... There's no shortcut to finding this. You can't reverse-engineer SHA-256. You can only guess. Trillions of times per second. Until you find a hash that works. That's called Proof of Work. And here's where it gets beautiful. Every block contains the hash of the previous block. So if someone tries to go back and tamper with an old transaction, their hash changes. Which changes the next block's hash. Which changes every block after that. The entire chain breaks. To fake one transaction, you'd have to redo the computational work for every block since then, faster than the entire rest of the network combined. That's economically impossible. The NSA built SHA-256 as a one-way function. A mathematical trapdoor. Easy to go in. Impossible to come back out. They were thinking about classified memos. They accidentally built the security foundation for an entirely new financial system. SHA-256 is in your browser right now. Your HTTPS connection. Your password manager. Your code signing certificates. It's everywhere. You just didn't know it. -- 📢 Follow saed ‎if you enjoyed this post 🔖 Be sure to subscribe to the newsletter: https://lnkd.in/eD7hgbnk 📹 Reach me on https://lnkd.in/eZ9mU5Ka for open DM's

Recent Update! After taking a break from my research and studies, I wanted to share some of my latest insights. I've been diving into "Real World Cryptography" by David Wong, and I recently learned more about SHA integrity checks that you often encounter when downloading software. You know, the 256-bit digest that verifies if your download is legitimate. However, SHA digests do more than just verify software integrity. They have three crucial security properties working behind the scenes: Security Properties of Hash Functions 1. Pre-Image Resistance This ensures that given a hash output (H), it is infeasible to reverse-engineer the input (m). Essentially, if 𝑓(𝑚)=𝐻, finding any input 𝑚′ such that 𝑓(𝑚′) =𝐻 should be practically impossible. 2. Second Pre-Image Resistance This property guarantees that given an input and its hash output, finding a different input that hashes to the same output is infeasible. In other words, given 𝑓(𝑚)=𝐻, you shouldn't be able to find 𝑚′ (where 𝑚≠𝑚′) such that 𝑓(𝑚′) =𝐻. 3. Collision Resistance This means that it should be impossible to find two different inputs that produce the same hash output. Essentially, finding a pair (𝑚, 𝑚′) where 𝑚≠𝑚′ and 𝑓(𝑚)=𝑓(𝑚′) should be unfeasible. Why 256-Bit Output? The minimum output size for a hash function in practice is 256 bits. Have you ever wondered why? This is because 256 bits make it virtually impossible to reach collision resistance limits. Here's the reasoning: In real-world cryptographic algorithms, aiming for a minimum of 128-bit security means an attacker would need to perform around 2^128 operations to break the algorithm (Only if there is a breakthrough in the computer system). For a hash function to ensure all three security properties mentioned above, it must provide at least 128 bits of security against all three types of attacks. The easiest attack, usually finding a collision due to the birthday paradox, requires the hash function to have at least a 256-bit output to maintain its security integrity. Understanding these properties and the reasoning behind the 256-bit requirement helps us appreciate the robust security measures that protect our digital world. #cryptography #learnings #preimage #secondpreimage #collision

Ever wondered what's happening in the background when you sign a transaction on blockchains like Bitcoin and Ethereum? One key component of signing a transaction is cryptographic hash functions - special algorithms that ensure data integrity and security. 🔑 What are they? Cryptographic hash functions transform data into a unique, fixed-length output. Even a tiny change to the input creates a completely different hash. To date, it is impossible to infer the data from the hash (even with the latest advances in quantum computing), although that can change in the future. But when you hear that quantum computers may kill Bitcoin... well...these hash functions are used everywhere: verifying file integrity, securing passwords, not just blockchain operations. So in that case also your bank account would not give you an alternative! ⚡ Secure Hashes Today SHA-2: Powers Bitcoin’s proof-of-work.  SHA-3: A newer, more secure algorithm used in Ethereum’s Keccak-256 variant. BLAKE2: Lightning-fast, secure, and versatile, but used less than SHA2 or SHA3 ✨ Why it Matters More secure hashes (like SHA-512) mean fewer risks of collisions, where two inputs produce the same hash. These algorithms are a cornerstone of modern cybersecurity. There is much research being done in quantum resistant algorithms, and by the time quantum computers are a threat (they are not currently!) we’ll probably have figured out an alternative 🙂