What is Cryptography?

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🔐 WHAT IS CRYPTOGRAPHY?

📘 Definition

Cryptography is the science of protecting information by converting it into a secure format so that only authorized persons can read or access it.

It ensures secure communication over insecure networks like the Internet.

The word Cryptography comes from:

  • Crypto = Hidden

  • Graphy = Writing

Meaning: “Hidden Writing”

🎯 Purpose of Cryptography

Cryptography is used to achieve:

  1. Confidentiality – Information is accessible only to authorized users.

  2. Integrity – Data cannot be altered without detection.

  3. Authentication – Verifies the identity of users.

  4. Non-repudiation – Sender cannot deny sending the message.

🔑 Basic Terminologies in Cryptography

1️⃣ Plaintext

Original readable message.

Example:
Hello Raj

2️⃣ Ciphertext

Encrypted unreadable message.

Example:
Xk39@Lp

3️⃣ Encryption

Process of converting plaintext into ciphertext.

4️⃣ Decryption

Process of converting ciphertext back into plaintext.

5️⃣ Key

A secret value used in encryption and decryption.

🔄 How Cryptography Works

Sender → Encrypts message using key → Sends ciphertext →
Receiver → Decrypts using key → Gets original message

🔥 Types of Cryptography

1️⃣ Symmetric Key Cryptography

  • Same key used for encryption and decryption.

  • Faster and simple.

  • Key must be kept secret.

Examples:

  • AES

  • DES

Advantage:

Fast performance.

Disadvantage:

Key sharing problem.

2️⃣ Asymmetric Key Cryptography

  • Uses two keys:

    • Public Key

    • Private Key

  • Public key encrypts.

  • Private key decrypts.

Examples:

  • RSA

  • ECC

Advantage:

More secure key exchange.

Disadvantage:

Slower than symmetric encryption.

3️⃣ Hash Functions

  • Converts data into fixed-length hash value.

  • One-way process (cannot reverse).

  • Used for password storage.

Examples:

  • SHA-256

  • MD5

🔐 Real-Life Applications of Cryptography

  • Online banking

  • ATM transactions

  • HTTPS websites

  • Email encryption

  • Digital signatures

  • Blockchain technology

  • Wi-Fi security

📌 Digital Signature

A digital signature is used to verify:

  • Sender identity

  • Data integrity

Used in:

  • Online contracts

  • E-filing

  • Government portals

🔒 SSL/TLS

Cryptography is used in SSL/TLS protocols to secure websites.

If website URL starts with:
https://

It means encryption is applied.

🔥 Advantages of Cryptography

  • Protects sensitive data

  • Prevents unauthorized access

  • Ensures secure communication

  • Protects financial transactions

⚠ Limitations of Cryptography

  • Key management is complex

  • If key is lost, data cannot be recovered

  • High computation cost

📊 Difference Between Encryption and Hashing

FeatureEncryptionHashing
ReversibleYesNo
Uses KeyYesNo (usually)
PurposeProtect dataVerify data integrity
ExampleAESSHA-256

🎓 Exam Short Note

Cryptography is the technique of securing information by converting readable data into unreadable format using encryption algorithms and keys to ensure confidentiality, integrity, authentication, and non-repudiation.

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