section_id,topic,content,example,difficulty
1,Introduction,"Cryptography is the practice of securing communication from adversaries.","encrypt(plaintext, key) -> ciphertext",Beginner
2,Symmetric Encryption,"Uses the same key for encryption and decryption.","AES, DES, XOR cipher",Beginner
3,Asymmetric Encryption,"Uses a public key for encryption and private key for decryption.","RSA, ECC, Diffie-Hellman",Intermediate
4,Hash Functions,"One-way functions that produce fixed-size output from variable input.","MD5, SHA-256, bcrypt",Beginner
5,XOR Cipher Basics,"XOR operation returns 1 when inputs differ, 0 when same.","0^1=1, 1^1=0, 0^0=0",Beginner
6,XOR Properties,"A XOR B XOR B = A (XORing twice returns original)","char encrypted = plain ^ key;",Beginner
7,Caesar Cipher,"Shift each letter by a fixed number of positions.","A+3=D, B+3=E, Z+3=C",Beginner
8,Caesar Implementation,"Use modulo arithmetic for wrapping.","encrypted = ((c - 'A' + shift) % 26) + 'A';",Intermediate
9,Vigenere Cipher,"Polyalphabetic substitution using a keyword.","KEY: ABC, Plain: HELLO",Intermediate
10,Binary File I/O,"Use rb and wb modes for binary file operations.","FILE *f = fopen(name, ""rb"");",Intermediate
11,Buffer Management,"Process large files in chunks to manage memory.","char buffer[4096];",Intermediate
12,Error Handling,"Always check return values of file operations.","if (fread(...) != expected) { ... }",Intermediate
13,Command Line Args,"Parse argc and argv for user options.","for(int i=1; i<argc; i++) {...}",Beginner
14,getopt Function,"Standard library function for parsing options.","while ((c = getopt(argc, argv, ""k:i:o:"")) != -1)",Intermediate
15,Key Management,"Never hardcode keys; read from arguments or files.","char *key = argv[optind];",Intermediate
16,Security Considerations,"Classic ciphers are educational; use modern crypto for real security.","Use OpenSSL for production",Advanced
17,Lorem Ipsum,"Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.","Filler text for testing",Beginner
18,Test Patterns,"Include various character types in test data.","ABCxyz123!@#",Beginner
19,Binary Patterns,"Test with binary-like strings.","01001000 01100101 01101100 01101100 01101111",Intermediate
20,Unicode Considerations,"Basic C handles ASCII; UTF-8 needs special handling.","wchar_t for wide characters",Advanced