Poland Liceum ogólnokształcące, klasa IV Computer science (extended level)
Chapters: 3
1. Using computers, digital devices and networks
Compression and networking
- Data Compression – Compression makes a file smaller so it uses less storage and travels faster. Lossless compression (RLE, Huffman, dictionary methods, ZIP, PNG) gives back exactly the original data. Lossy compression (JPEG, MP3, MP4) removes detail people hardly notice, so files get much smaller but the lost detail cannot return. Compression ratio = original size ÷ compressed size.
2. Developing social competences
Team projects and careers
Coming soon
3. Law and safety
Authentication and cryptography
- Cryptography: How Secret Messages Keep Data Safe – Cryptography is the science of keeping messages secret and trustworthy. A normal message (plaintext) is mixed with a key to make a secret message (ciphertext); this is encryption. Turning it back with the right key is decryption. Old ciphers like the Caesar cipher shift letters. Modern systems use symmetric encryption (one shared key) and asymmetric or public-key encryption (a public key to lock, a private key to unlock). Hashing makes a fixed-length fingerprint of data to check it was not changed, and digital signatures prove who sent a message. Your phone uses all of these every time you open a website with https or send a chat message.