Cryptography Fundamentals

Cryptography is the science of securing communication and data through mathematical algorithms. It is the foundation of confidentiality, integrity, and authentication in cybersecurity.

---

Core Concepts

Term	Definition
Plaintext	The original readable data
Ciphertext	The encrypted (unreadable) data
Encryption	Converting plaintext to ciphertext
Decryption	Converting ciphertext back to plaintext
Key	A secret value used by the algorithm to encrypt/decrypt
Algorithm (cipher)	The mathematical function used for encryption

Plaintext  ──[Encryption + Key]──▶  Ciphertext
Ciphertext ──[Decryption + Key]──▶  Plaintext

---

Symmetric Encryption

Symmetric encryption uses the same key for encryption and decryption:

Algorithm	Key Size	Notes
AES	128, 192, 256 bits	Industry standard — used everywhere
3DES (Triple DES)	168 bits	Legacy — being phased out
ChaCha20	256 bits	Modern, fast on mobile devices
Blowfish / Twofish	Up to 448 bits	Older alternatives

AES (Advanced Encryption Standard)

AES is the most widely used symmetric cipher: