Need Clarification on Cryptographic Hash Functions

I’ve been diving into the world of cryptography and I’m a bit confused about cryptographic hash functions. I understand that they’re a crucial component, but I’m having trouble grasping their applications and why they’re considered secure. Could someone shed some light on this for me?

Absolutely! Cryptographic hash functions are essential tools in cybersecurity. They’re designed to take an input (message) and produce a fixed-size hash value, which is a seemingly random string of characters. One key property is that a tiny change in the input will produce a significantly different hash. This makes them perfect for data integrity checks, password hashing, and digital signatures. They’re secure because they’re designed to be irreversible and resistant to collisions (different inputs producing the same hash).

To add to @morti1cia explanation, hash functions are widely used for password storage. Instead of storing actual passwords, systems store the hash of the password. When a user logs in, the system hashes the entered password and compares it to the stored hash. Even if the database is compromised, attackers can’t easily reverse the hash to get the original password. It’s a critical defense against data breaches.

Hash functions also play a crucial role in digital signatures. In this context, a hash of a message is created and then encrypted with a private key to produce a digital signature. When someone receives the message and the digital signature, they can decrypt the signature with the sender’s public key and compare it to a hash of the received message. If they match, it verifies the authenticity and integrity of the message.

Remember that while hash functions are secure and one-way, they’re not immune to attacks. Brute force attacks and rainbow table attacks can still compromise weakly hashed passwords. That’s why it’s important to use salted hashes for passwords – a unique salt is added to each password before hashing, making it much harder to crack using precomputed tables.

I had a similar question not too long ago! One thing that helped me understand hash functions better is learning about their properties like the Avalanche Effect (small changes in input drastically change output) and the Preimage Resistance (given a hash, it’s computationally infeasible to find the original input). Also, exploring real-world examples of attacks and defenses using hash functions can provide great insights.

Hope this clarifies things for you! Feel free to ask more questions.

That makes a lot of sense. It’s one of those things where you know what it is but it’s a little tricky tying to find the words to properly explain it. Thanks, everyone!

Rainbow tables work when the hash is not “salted”. Salt is random data added to the data to be hashed, which is stored with the resultant hash, because it is needed to recreate the hash for comparison.

For instance, a non-salted SHA1 hash can easily be cracked with a rainbow table. You simply create a list of passwords you want to try, SHA1 hash each one, and store it with the password. Then, you can sort by the hash value to speed up a binary search. This type of search is incredibly fast:

Binary search runs in logarithmic time in the worst case, making O ( log ⁡ n ) O(og n) comparisons, where n n is the number of elements in the array.[a][6

Binary Search

So, you can make a rainbow table like this:


If the number of items in the list is 256, at most, it should take fewer than 8 attempts (2^8) to match the hash. Then, you just look at the password in the line.

I would just generate a list like this, and then use grep to find the hash I’m looking for.

You could also use a GPU, which hashes passwords in GPU memory and compares them against the candidate hash. This is super fast, and it can be done even on salted passwords. Rainbow tables get large and unwieldy when the password space is large, but for a limited set of passwords with unsalted hashes, a rainbow table should be even faster than a GPU.