Complete Encryption Guide

1. Fundamentals of Encryption

Encryption transforms readable data (plaintext) into an unreadable format (ciphertext) using a mathematical algorithm and a key. Only those with the correct key can decrypt the ciphertext back to plaintext. Encryption protects data confidentiality—even if data is intercepted, it's useless without the key.

Modern cryptography provides four fundamental services:

• Confidentiality: Data is secret (encryption)
• Integrity: Data hasn't been modified (hashing, MACs)
• Authentication: Verify identity of sender (digital signatures)
• Non-repudiation: Sender can't deny sending (digital signatures)

2. Symmetric Encryption

Symmetric encryption uses the same key for both encryption and decryption. It's fast and efficient for encrypting large amounts of data.

2.1 AES (Advanced Encryption Standard)

AES is the most widely used symmetric algorithm. It's a block cipher that encrypts data in 128-bit blocks with key sizes of 128, 192, or 256 bits.

# Python AES-GCM encryption
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
import os

# Generate 256-bit key
key = AESGCM.generate_key(bit_length=256)
aesgcm = AESGCM(key)

# Encrypt
nonce = os.urandom(12)  # Must be unique per message
ciphertext = aesgcm.encrypt(nonce, plaintext, associated_data)

# Decrypt
plaintext = aesgcm.decrypt(nonce, ciphertext, associated_data)

3. Asymmetric Encryption

Asymmetric (public-key) encryption uses key pairs: a public key for encryption and a private key for decryption. Anyone can encrypt with your public key, but only you can decrypt with your private key.

3.1 RSA

RSA is the most common asymmetric algorithm. Key sizes of 2048 or 4096 bits are recommended. RSA is slow, so it's typically used to encrypt symmetric keys rather than data directly.

# RSA key generation
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization

private_key = rsa.generate_private_key(
    public_exponent=65537,
    key_size=4096
)
public_key = private_key.public_key()

3.2 Elliptic Curve Cryptography (ECC)

ECC provides equivalent security to RSA with smaller key sizes, making it faster and more efficient. Ed25519 and secp256k1 are popular curves.

4. Cryptographic Hashing

Hash functions create fixed-size outputs (digests) from any input. They're one-way functions—you can't recover the input from the hash. Any change to the input produces a completely different hash.

4.1 Hash Algorithms

# Python hashing
import hashlib

# SHA-256
hash_object = hashlib.sha256(b"message")
digest = hash_object.hexdigest()

# HMAC (keyed hash for authentication)
import hmac
mac = hmac.new(key, message, hashlib.sha256).hexdigest()

5. Digital Signatures

Digital signatures use asymmetric cryptography to provide authentication and non-repudiation. You sign with your private key; anyone can verify with your public key.

# Create signature
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding

signature = private_key.sign(
    message,
    padding.PSS(
        mgf=padding.MGF1(hashes.SHA256()),
        salt_length=padding.PSS.MAX_LENGTH
    ),
    hashes.SHA256()
)

# Verify signature
public_key.verify(signature, message, padding, hashes)

6. Practical Applications

6.1 File Encryption

# GPG file encryption
gpg -c sensitive.txt             # Symmetric encryption
gpg -e -r [email protected] sensitive.txt  # Asymmetric

# OpenSSL
openssl enc -aes-256-cbc -salt -in file.txt -out file.enc
openssl enc -d -aes-256-cbc -in file.enc -out file.txt

6.2 Disk Encryption

• BitLocker: Windows full-disk encryption
• FileVault: macOS full-disk encryption
• LUKS: Linux standard disk encryption
• VeraCrypt: Cross-platform container encryption

6.3 TLS Handshake

TLS combines all cryptographic primitives: asymmetric for key exchange, symmetric for data encryption, hashing for integrity, signatures for authentication.

7. Implementation Guidelines

7.1 Key Management

• Generate keys using cryptographically secure random generators
• Store keys securely (HSM, secrets manager, key vault)
• Rotate keys regularly
• Implement key revocation procedures

8. Frequently Asked Questions

Conclusion

Encryption is fundamental to digital security. Understand when to use symmetric vs asymmetric encryption, always use authenticated encryption modes, and never implement cryptography yourself—use well-tested libraries. Key management is often the biggest challenge; focus on securing your keys as much as choosing strong algorithms.

Continue Learning:
SSL/TLS Guide Password Security