The Cryptography Landscape

How your course algorithms fit together

Mission tie-in: Your exam tests step-by-step traces of DES, RC4, Diffie-Hellman, SHA-1, and RSA. This lesson gives you the map so each algorithm has a place in your head before you drill the math.

Intro theory (CIA, threat layers, Sec-SDLC) lives in Intro Playlist Concepts — this page is the algorithm map only.

Two families of ciphers

Symmetric

Same key to lock & unlock

DES (block, 64-bit chunks) and RC4 (stream, byte-by-byte) both use one shared secret key.

Problem: How do two people agree on the key over the internet?

Asymmetric

Key pair: public + private

RSA encrypts with public key, decrypts with private. Diffie-Hellman agrees on a shared secret without sending it.

Trade-off: Slower, but solves key distribution.

Visual: where each algorithm sits

Security Goals: CIA Confidentiality → Ciphers Integrity → Hash symmetric asymmetric DES Block · 64 bits RC4 Stream · XOR RSA Encrypt / Sign Diffie-Hellman Key agreement SHA-1 One-way · 160-bit digest

Cipher vs hash — don't mix them up

Cipher (DES, RC4, RSA)Hash (SHA-1)
Reversible?Yes — decrypt to get plaintextNo — cannot recover message
Needs key?Yes (shared or public/private)No key — deterministic function
Exam skillEncrypt/decrypt tracesPadding + compression rounds
One-bit input changeCiphertext changes (roughly half the bits)Completely different hash (avalanche)

Block vs stream (symmetric only)

DES waits until it has 64 bits, then transforms the whole block through 16 Feistel rounds. RC4 generates a keystream one byte at a time and XORs it with each plaintext byte — no fixed block size.

Retrieval practice

Which algorithm solves the key distribution problem without encrypting the message itself?

Retrieval practice

Which pair are both symmetric ciphers taught in your course?

Stuck? Ask your AI teacher follow-up questions — e.g. "Walk me through why DES is a Feistel cipher" or "Quiz me on symmetric vs asymmetric."