Different uses of hashing

🧠 PART 1 — WHAT IS HASHING? (FROM ZERO)

💡 Start with a problem

Imagine you store a password:

mypassword123

If someone hacks the system:

👉 They can see the password 😬

🔐 Solution: Hashing

Instead of storing the password, we store a hash

💡 What is a hash?

👉 A hash is the output of a function that turns data into a fixed-length string.

Example:

mypassword123 → 9f86d081884c7d65

👉 That output = hash value

⚠ Important properties (YOU MUST KNOW)

1. One-way
   

   • 
     You cannot reverse it easily
     

   • 
     You can’t get the original data back
     

2. Same input → same output
   

   • 
     Always consistent
     

3. Small change → completely different hash
   

Example:

password → 5f4dcc3b5aa  
Password → 7c6a180b368

🔥 KEY IDEA

👉 Hashing is NOT encryption

👉 You cannot decrypt a hash

🧠 PART 2 — USES OF HASHING (WHAT OCR CARES ABOUT)

🔵 1. Password Storage

💡 How it works

1. 
   User creates password
   

2. 
   System hashes it
   

3. 
   Hash is stored (NOT the password)
   

🔄 Login process

1. 
   User enters password
   

2. 
   System hashes it again
   

3. 
   Compares hashes
   

✔ If same → access granted

❌ If different → denied

🔐 Why this is good

Even if hacked:

👉 attacker only sees hashes, not passwords

🔴 2. Data Integrity (Checking data hasn’t changed)

💡 Problem

You download a file — how do you know it wasn’t changed?

💡 Solution

1. 
   Original file has a hash
   

2. 
   You download file
   

3. 
   Your computer hashes it
   

4. 
   Compare hashes
   

✔ Same → file is safe

❌ Different → file has been altered

🟢 3. Digital Signatures (simplified)

Used to verify:

• 
  sender identity
  

• 
  data integrity
  

👉 Instead of signing the whole file:

• 
  hash is created
  

• 
  hash is signed
  

Faster and efficient

⚖ ADVANTAGES & DISADVANTAGES

✅ Advantages of Hashing

• 
  Protects passwords (not stored directly)
  

• 
  Fast to compute
  

• 
  Ensures data integrity
  

• 
  Fixed output size (efficient)
  

• 
  One-way (secure)
  

❌ Disadvantages of Hashing

• 
  Cannot retrieve original data
  

• 
  Vulnerable to brute force attacks (guessing inputs)
  

• 
  Possible collisions (two inputs give same hash — rare but possible)
  

• 
  Needs extra security (e.g. salting — not required in depth for OCR)