Cryptography – Post 1: Hashing Basics

Cryptography – Post 1: Hashing Basics

I’ve recently started diving into cryptography — not from the headlines, but from the ground up.
I’m starting with hashing: what it is, how it works, and where it shows up in real systems.

What is Hashing?

Hashing is the process of turning any piece of data (text, password, file, etc.) into a fixed-length, irreversible string — called a hash or digest.

A good hash function has these properties:

• Deterministic → same input = same output
• One-way → you can’t go backwards
• Collision-resistant → different inputs = different outputs
• Fixed-size output → regardless of input length

Hashing vs. Encryption

Feature	Hashing	Encryption
Direction	One-way (irreversible)	Two-way (encrypt & decrypt)
Output length	Fixed	Variable
Main purpose	Verify, compare, fingerprint	Hide content from unauthorized access
Examples	Password storage, checksums	Securing messages, files, etc.

Basic Hashing in Python (SHA-256)

import hashlib

msg = "hello world"
hashed = hashlib.sha256(msg.encode()).hexdigest()
print(hashed)

Output:

nginxKopierenBearbeitenb94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

Even changing 1 character would give a completely different hash.

Where Is Hashing Used?

1. Password storage –
   Instead of saving the password directly, you save only the hash of it.
   When the user logs in, hash their input and compare the result.
2. File integrity checks –
   Sites often share SHA256 hashes of files.
   If your download has a different hash, it’s been tampered with.
3. Digital signatures –
   Hashing ensures the data being signed is authentic and unchanged.
4. Blockchain –
   Each block stores a hash of the previous block, linking the chain.

Not All Hash Functions Are Equal

Function	Length	Status
MD5	128-bit	Broken (collisions found)
SHA-1	160-bit	Broken
SHA-256	256-bit	Strong (used in Bitcoin)
SHA-512	512-bit	Strong, longer

Older functions like md5 or sha1 are not secure for passwords or sensitive data anymore.

Why Use Salt?

Even though hashing is irreversible, there’s still a risk:

If two people use the same password, their hashes will be identical — which helps attackers.

Solution: Add a unique salt (random string) to each password before hashing.

password = "password123"
salt = "a8#r@9k*"
combined = password + salt
hashed = hashlib.sha256(combined.encode()).hexdigest()

Now even if two users have the same password, their hashes will differ.

Summary

• Hashing is NOT encryption — it’s a one-way transformation.
• It’s everywhere: login systems, downloads, blockchains.
• Strong algorithms like SHA-256 are essential.
• Salting is required for secure password hashing.
• Hashing is often the first step before doing more advanced cryptography like digital signatures or encryption.