Cryptography

Modern Symmetric

AES and friends.

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160 XP
AES Basics
Block cipher, 128-bit blocks, and why ECB leaks.
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180 XP
Block Cipher Modes
ECB vs CBC vs CTR vs GCM — and why IVs matter.
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170 XP
Padding
PKCS#7, why a whole extra block, and the padding oracle.
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190 XP
Authenticated Encryption
AEAD, tags, AAD, and picking GCM vs ChaCha20-Poly1305.
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200 XP
Key Derivation
PBKDF2 → scrypt → Argon2: making passwords expensive.
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200 XP
Stream Ciphers
ChaCha20, RC4, and the keystream-XOR mental model.
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220 XP
Nonce Management
GCM nonce-reuse, deterministic vs random, the birthday bound, XChaCha20 fix.
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200 XP
Disk Encryption (XTS)
Why FileVault, BitLocker, and LUKS use a different mode than TLS.
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200 XP
TLS 1.3 Symmetric Layer
AES-GCM vs ChaCha20-Poly1305 — when each wins.
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