Compression, Encryption & Hashing

Lossless compression should be used because:

• It does not permanently remove any data.

• The original data can be fully reconstructed/restored after decompression.

• This is important because the user is sending text, so losing data could make it unreadable or change its meaning.

🧠 Easy way to remember:“NO LOSS = EXACT TEXT”

Lossless = No data lost → Original restored → Text stays correct

A good way to remember this is:

🔐 Encryption = LOCK it, so it can be UNLOCKED.
#⃣ Hashing = FINGERPRINT it, so it can be CHECKED.

Encryption converts readable data (plaintext) into unreadable ciphertext using an encryption algorithm and a key. It is reversible, so the original data can be recovered using the correct key.

There are two main types of encryption:

• Symmetric encryption uses the same key to encrypt and decrypt the data. This is useful for the robot because large amounts of stored data or network communication can be encrypted and decrypted efficiently. However, the key must be kept secret and securely shared.

• Asymmetric encryption uses a public key and a private key. The public key can be shared, while the private key is kept secret. Data encrypted with the public key can be decrypted using the corresponding private key. It can therefore be used whenrobots/users need to communicate securely without already sharing a secret key. It can also help verify the identity of the sender.

For the robot's stored data, encryption is useful because if someone gains unauthorised access to the robot's storage, they will see ciphertext rather than the original information. The data can only be understood if the attacker has the correct key. Therefore, encryption provides confidentiality.

For communication over the wireless network, encryption is important because wireless data could be intercepted. Encryption means that an attacker who intercepts the transmission cannot understand the data without the key. Asymmetric encryption can be used to securely establish/share a key, while symmetric encryption can then efficiently protect the actual communication.

Hashing is different from encryption. Hashing is a one-way process that converts data into a fixed-length hash value. The original data should be practically impossible to obtain from the hash. Therefore, hashing is suitable for information that does not needto be retrieved in its original form, such as the robot's users' passwords.

For example, instead of storing a user's password, the robot could store its hash. When the user enters their password, the robot hashes the entered password and compares the result with the stored hash. If the hashes match, the password is considered correct. If an attacker steals the stored hashes, they cannot simply decrypt them to obtain the original passwords.

Hashing can also be used to check whether data has been changed or corrupted, because changing the input produces a different hash.

Therefore, encryption is better for most of the robot's stored data and communications, because the robot needs to be able to recover and use the original data. Hashing is better for passwords and other data that only needs to be verified, because it is one-way.

🧠 The exam-memorytrick:“LOCK vs FINGERPRINT”

	🔐 Encryption	#⃣ Hashing
Main purpose	Keep data secret	Check/verify data
Reversible?	Yes	No / one-way
Uses a key?	Yes	No encryption key
Stored passwords?	❌ Not ideal	✅ Ideal
Data the robot needs to read again?	✅ Yes	❌ No
Wireless communication?	✅ Yes	❌ Not for confidentiality
If intercepted	Cannot be understood without key	Hash alone does not provide confidentiality

The customer has to choose between lossy and lossless compression:

• Lossy permanently removes some data, so the video has a smaller file size but its quality is reduced.

• Lossless rewrites the data into a more efficient format without losing information, so the original video can be recreated and the original quality ismaintained, but the file size is larger than with lossy compression.

• With lossy compression, the compression ratio can be adjusted depending on theavailable bandwidth. This can make the video buffer less and start playing quicker, especially on a slower connection, although there may be a noticeable decrease in quality.

• With lossless compression, more data needs to be streamed, so it can buffer more and take longer to start watching, but the customer gets higher-quality video.

  
  

🧠 Easy way toremember:

LOSSY = Less data → Lower quality → Less buffering
LOSSLESS = No data lost → Original quality → More buffering

i. Lossy compression. ✅ [1]

ii. Photographs are compressed because it reduces the size of the image file, meaning they use less bandwidth when transmitted and take up less storage space on the web server. ✅ [2]

🧠 Memorytrick:“Small → Send → Store”

• Small = smaller image file

• Send = less bandwidth needed to send it

• Store = less storage space on the server