Cryptography from Scratch| Master Cryptography in Java

Define cryptography as the study of techniques for secure communication, and demonstrate encryption turning plain text into cipher text and decryption restoring it for authorized readers, with Java implementations.

Explore the history of cryptography, from Enigma to modern practices, and learn why we test cryptographic algorithms and seek mathematical proof rather than assuming unbreakable security.

Explore how public encryption and decryption functions rely on a secret key, why key secrecy matters, and how secure channels exchange keys to protect plaintext and ciphertext from brute-force threats.

Explore the substitution cipher, a historic, simple replacement method, and learn how brute-force and frequency analysis break it, along with practical defenses against social engineering and side-channel attacks.

Implement a substitution cipher in Java using encryption and decryption maps to translate letters, preserve case, and learn a frequency analysis approach to cracking it.

Explain how the Caesar cipher shifts letters with a modulo 26 key to encrypt and decrypt, and why brute-force and frequency analysis break it.

Implement a Caesar cipher in Java with encrypt and decrypt functions, handle uppercase and lowercase letters, wrap around after Z, and demonstrate a brute-force break of the cipher.

This lecture explains affine cipher with keys a and b, encryption x -> a x + b mod 26, covers decryption and how brute-force and frequency analysis reveal cipher.

Master the affine cipher by encrypting with keys A and B, mapping letters to 0-25, and decrypting via the multiplicative inverse modulo 26 with proper case handling.

Demonstrates stream cipher basics: encrypt bits individually with a key bit using XOR (modulo 2), contrasting with block ciphers, and shows decryption using the same key stream.

Encrypt and decrypt messages using an xor cipher with a password as the key in Java, applying character-wise xor and modulo indexing to handle key length.

Explore random number generators for cryptography, from true random sources like coin flips and dice to seeded, pseudo-random sequences, and finally cryptographically secure generators with unpredictable outputs.

The lecture presents a secure cipher using a truly random per-bit keystream. It uses keystream blocks only once and notes the drawback of a key length equal to the message.

Explore aes, the advanced encryption standard, a 128-bit block cipher with 128–256 bit keys, rounds, round keys, substitution via a box, shift rows, and mix columns via galois field multiplication.

Discover how asymmetric encryption secures messages with a public key for encryption and a private key for decryption, while private keys enable digital signatures verified by public keys.