Encryption Fundamentals - Cryptographic Technologies for Protecting Data

What is Encryption?

Encryption is a technology that transforms data into a format that third parties cannot read. Only those with the correct key can restore (decrypt) the original data.

Why is it needed: To address risks of data falling into third-party hands through communication eavesdropping, unauthorized database access, or device loss.

Types of Encryption

Symmetric Encryption

Uses the same key for both encryption and decryption.

flowchart LR
    P1["Plaintext"] -->|"Shared Key"| E["Encrypt"]
    E --> C["Ciphertext"]
    C -->|"Shared Key (same)"| D["Decrypt"]
    D --> P2["Plaintext"]

Common Algorithms

Implementation Example

const crypto = require('crypto');

// Encryption
function encrypt(text, key) {
  const iv = crypto.randomBytes(16);
  const cipher = crypto.createCipheriv('aes-256-gcm', key, iv);
  let encrypted = cipher.update(text, 'utf8', 'hex');
  encrypted += cipher.final('hex');
  const authTag = cipher.getAuthTag();
  return {
    iv: iv.toString('hex'),
    encrypted,
    authTag: authTag.toString('hex')
  };
}

// Decryption
function decrypt(encryptedData, key) {
  const decipher = crypto.createDecipheriv(
    'aes-256-gcm',
    key,
    Buffer.from(encryptedData.iv, 'hex')
  );
  decipher.setAuthTag(Buffer.from(encryptedData.authTag, 'hex'));
  let decrypted = decipher.update(encryptedData.encrypted, 'hex', 'utf8');
  decrypted += decipher.final('utf8');
  return decrypted;
}

Advantages and Disadvantages

Public Key Encryption (Asymmetric)

Uses different keys (public key and private key) for encryption and decryption.

flowchart LR
    subgraph Receiver["Receiver"]
        Priv["Private Key<br/>(held only by receiver)"]
        Pub["Public Key<br/>(publicly available)"]
    end

    subgraph Sender["Sender"]
        P1["Plaintext"]
    end

    Pub -->|"Get public key"| P1
    P1 -->|"Encrypt with public key"| C["Ciphertext"]
    C -->|"Decrypt with private key"| P2["Plaintext"]
    Priv --> P2

Common Algorithms

Digital Signatures

Sign with private key, verify with public key.

flowchart LR
    subgraph Sender["Sender (signing)"]
        D["Data"]
    end
    subgraph Receiver["Receiver (verifying)"]
        R["Authentic/Forged"]
    end

    D -->|"Sign with private key"| S["Signature"]
    S -->|"Verify with public key"| R

Advantages and Disadvantages

Hybrid Encryption

In practice, both methods are combined.

Hash Functions

Generate a fixed-length hash value from arbitrary-length data. The original data cannot be recovered.

A single character change produces a completely different hash

Common Algorithms

Password Hashing

const bcrypt = require('bcrypt');

// Hash password
async function hashPassword(password) {
  const saltRounds = 12;
  return await bcrypt.hash(password, saltRounds);
}

// Verify password
async function verifyPassword(password, hash) {
  return await bcrypt.compare(password, hash);
}

// Usage example
const hash = await hashPassword('mypassword123');
// → "$2b$12$LQv3c1yqBWVHxkd0LHAkCOYz6TtxMQJqhN8..."

const isValid = await verifyPassword('mypassword123', hash);
// → true

Always hash passwords before storing: Storing in plaintext is absolutely not acceptable. Use salted hash functions (bcrypt, Argon2).

Selection by Use Case

Summary

Encryption is a foundational technology for data security. Symmetric encryption is fast and suitable for encrypting large amounts of data, while public key encryption is suitable for key distribution and authentication. In practice, hybrid encryption combining both is used. Always use salted hash functions for password storage.