🔑 Cryptography Lab

Explore encryption algorithms — from classical ciphers to modern RSA, AES, and cryptographic hashing. Interactive simulators let you see every step of the process.

Symmetric Encryption

Same key encrypts and decrypts. Fast and efficient for bulk data. Examples: AES, DES, Blowfish.

Use when: encrypting files, database columns, or large volumes of data where both parties already share a secret key.

Asymmetric Encryption

Public key encrypts, private key decrypts. Solves key distribution. Examples: RSA, ECC, DSA.

Use when: key exchange, digital signatures, TLS/SSL certificates, and scenarios where parties have never shared a secret.

Input Text

Shift: 3

125

Encrypted

KHOOR

Decrypted

HELLO

Substitution Table

↓

Algorithm Comparison

Algorithm	Type	Key Size	Speed	Use Case
AES	Symmetric	128/256 bits	Fast	Data at rest, TLS
DES	Symmetric	56 bits	Fast	Legacy systems
RSA	Asymmetric	2048/4096 bits	Slow	Key exchange, signatures
ECC	Asymmetric	256 bits	Moderate	Mobile, IoT, TLS
Blowfish	Symmetric	32-448 bits	Fast	File encryption
DSA	Asymmetric	1024/2048 bits	Slow	Digital signatures

Cryptography Interview Questions

1. What is the difference between symmetric and asymmetric encryption?

Symmetric encryption uses the same key for encryption and decryption (e.g., AES). Asymmetric encryption uses a public key to encrypt and a private key to decrypt (e.g., RSA). Symmetric is faster but requires secure key exchange; asymmetric solves key distribution but is computationally expensive.

2. How does RSA encryption work?

RSA relies on the difficulty of factoring large primes. Two large primes p and q are chosen, n = p × q, φ(n) = (p-1)(q-1). A public exponent e is chosen (typically 65537), and the private key d = e⁻¹ mod φ(n). Encryption: c = m^e mod n. Decryption: m = c^d mod n.

3. What is the difference between hashing and encryption?

Hashing is a one-way function that produces a fixed-size output; it cannot be reversed. Encryption is a two-way function that can be decrypted with the proper key. Hashing is used for integrity checks and password storage; encryption is used for confidentiality.

4. What is a digital signature and how does it work?

A digital signature provides authenticity and non-repudiation. The sender hashes the message and encrypts the hash with their private key. The receiver decrypts the hash with the sender's public key and compares it to the hash of the received message. If they match, the message is authentic.

5. What is the AES encryption algorithm?

AES (Advanced Encryption Standard) is a symmetric block cipher that operates on 128-bit blocks with 128/192/256-bit keys. It uses multiple rounds (10/12/14) of SubBytes, ShiftRows, MixColumns, and AddRoundKey operations. It is the standard for modern symmetric encryption.

AES Encryption Code Examples

Python

from cryptography.fernet import Fernet

# Generate a key
key = Fernet.generate_key()
cipher = Fernet(key)

# Encrypt
plaintext = b"Sensitive data"
ciphertext = cipher.encrypt(plaintext)

# Decrypt
decrypted = cipher.decrypt(ciphertext)
print(decrypted.decode())

JavaScript (Node.js)

const crypto = require('crypto');

const algorithm = 'aes-256-cbc';
const key = crypto.randomBytes(32);
const iv = crypto.randomBytes(16);

function encrypt(text) {
  const cipher = crypto.createCipheriv(algorithm, key, iv);
  let encrypted = cipher.update(text, 'utf8', 'hex');
  encrypted += cipher.final('hex');
  return encrypted;
}

function decrypt(encrypted) {
  const decipher = crypto.createDecipheriv(algorithm, key, iv);
  let decrypted = decipher.update(encrypted, 'hex', 'utf8');
  decrypted += decipher.final('utf8');
  return decrypted;
}

package main

import (
  "crypto/aes"
  "crypto/cipher"
  "crypto/rand"
  "fmt"
)

func main() {
  key := []byte("examplekey123456")
  plaintext := []byte("Hello, AES!")

  block, _ := aes.NewCipher(key)
  aesGCM, _ := cipher.NewGCM(block)

  nonce := make([]byte, aesGCM.NonceSize())
  rand.Read(nonce)

  ciphertext := aesGCM.Seal(nil, nonce, plaintext, nil)
  fmt.Printf("Encrypted: %x\n", ciphertext)
}