Symmetric Encryption and Block Ciphers Questions

How symmetric-key primitives are constructed and why they work: block-cipher internals (Feistel networks vs substitution-permutation networks, the AES round structure and S-box design, key schedules and why a weak one degrades security), stream ciphers (ChaCha20 and CTR-mode keystream generation), and the internal mechanics of modes of operation (ECB, CBC, CTR, XTS, GCM), including why some are parallelizable, why ECB leaks structure, and why some require a unique nonce. Covers authenticated encryption construction internals (how GHASH and Poly1305 work, why nonce reuse breaks their security algebraically, formal security notions like IND-CPA and INT-CTXT), padding schemes and the mechanics of padding-oracle attacks, and cryptanalysis of block ciphers (differential and linear cryptanalysis, reduced-round attacks). This is the design and internals layer: how these primitives are built and proven secure, distinct from choosing which algorithm or mode to deploy, managing key lifecycle and rotation, or architecting data protection for a system, which belong to the applied cryptography layer.