Hashing algorithms (MD5, SHA)

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🔐 HASHING ALGORITHMS (MD5, SHA)

📘 What is Hashing?

Hashing is the process of converting data (message, file, password) into a fixed-length string of characters using a mathematical algorithm.

The output is called a Hash Value or Message Digest.

⚠ Important:
Hashing is a one-way process — it cannot be reversed.

🎯 Purpose of Hashing

Hashing is mainly used for:

  1. Data Integrity

  2. Password Storage

  3. Digital Signatures

  4. File Verification

  5. Blockchain technology

🔑 Important Characteristics of Hash Functions

A good hashing algorithm must:

  • Produce fixed-length output

  • Be one-way (irreversible)

  • Be fast to compute

  • Avoid collisions (two inputs should not produce same hash)

  • Show avalanche effect (small input change → big output change)

📌 What is a Collision?

A collision occurs when two different inputs produce the same hash value.

Strong hash functions minimize collisions.

🔢 Example of Hashing

Input:
Hello

MD5 Output:
8b1a9953c4611296a827abf8c47804d7

SHA-256 Output:
185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969

Notice:
Even a small change in input changes the entire hash.

1️⃣ MD5 (Message Digest Algorithm 5)

📘 Definition

MD5 is a widely used cryptographic hash function that produces a 128-bit hash value.

Developed by Ronald Rivest in 1991.

🔑 Features

  • Produces 128-bit hash

  • Output length: 32 hexadecimal characters

  • Fast processing

  • Now considered insecure

❌ Weakness of MD5

  • Vulnerable to collision attacks

  • Not secure for passwords

  • Not recommended for cryptographic security

✅ Current Uses (Limited)

  • File integrity checks

  • Non-security applications

2️⃣ SHA (Secure Hash Algorithm)

📘 Definition

SHA is a family of cryptographic hash functions developed by NIST (National Institute of Standards and Technology).

🔥 SHA Family

1️⃣ SHA-1

  • 160-bit hash

  • Now insecure

  • Vulnerable to collisions

2️⃣ SHA-2 (Most Common Today)

Includes:

  • SHA-224

  • SHA-256

  • SHA-384

  • SHA-512

Most popular: SHA-256

3️⃣ SHA-3

  • Latest version

  • More secure structure

  • Different algorithm design

🔑 SHA-256 Features

  • Produces 256-bit hash

  • Very secure

  • Used in blockchain

  • Used in SSL/TLS

  • Used in digital certificates

🔥 MD5 vs SHA Comparison

FeatureMD5SHA-1SHA-256
Output Size128-bit160-bit256-bit
SecurityWeakWeakStrong
SpeedFastModerateSlightly slower
Collision ResistancePoorWeakStrong
Recommended Today❌ No❌ No✅ Yes

🔐 Hashing vs Encryption

FeatureHashingEncryption
ReversibleNoYes
Uses KeyNoYes
PurposeData integrityData confidentiality
ExampleSHA-256AES

🛡 Real-Life Applications of SHA-256

  • Password storage

  • Blockchain (Bitcoin)

  • SSL certificates

  • Digital signatures

  • Secure file verification

🎯 Why MD5 and SHA-1 Are Not Secure?

  • Advanced computing can find collisions.

  • Hackers can generate fake certificates.

  • Password cracking tools can break weak hashes.

Therefore, modern systems use:

  • SHA-256

  • SHA-3

  • Bcrypt

  • PBKDF2

🎓 Exam Important Short Note

Hashing algorithms like MD5 and SHA convert data into fixed-length hash values to ensure data integrity. MD5 produces a 128-bit hash but is insecure, while SHA-256 produces a 256-bit hash and is widely used for secure applications.

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