It gives an introduction on the Encryption Ciphers

1. Stream Cipher and
Block Cipher

2. Learning Objectives
• By the end of this session, students will be able to:
• Define stream ciphers and block ciphers
• Explain how each cipher works
• Compare security and performance
• Identify suitable cloud use cases
• Justify cipher selection in assignments

3. What is a Cipher?
• A cipher is a cryptographic algorithm
• Converts plaintext → ciphertext
• Uses a secret key
• Ensures confidentiality of data
• Core component of encryption systems

4. Why Ciphers are important in Cloud
• Cloud data is stored remotely
• Shared infrastructure risks
• Data travels across networks
• Encryption protects data at:
• Rest
• Transit
• Processing

5. Classification of Ciphers
• Ciphers are classified based on:
• Data processing method
• Size of data units
• Encryption workflow
• Two main types:
1. Stream Cipher
2.Block Cipher

6. Stream Cipher
• Encrypts data bit-by-bit or byte-by-byte
• Uses a keystream
• Encryption uses XOR operation
• Formula:
Ciphertext = Plaintext Keystream
⊕

7. Stream Cipher Working
1.Secret key is provided
2.Keystream generator produces pseudo-random bits
3.Each plaintext bit is XORed
4.Ciphertext is generated
5.Same process used for decryption

8. Stream Cipher Examples
• RC4 ❌ (broken, insecure)
• Salsa20
• ChaCha20 ✅ (modern & secure)
• SNOW 3G (mobile networks)

9. Advantages Of Stream Ciphers
• Very fast encryption
• Low memory usage
• No padding required
• Suitable for real-time data
• Low latency

10. Disadvantages Of Stream Ciphers
• Keystream reuse causes total compromise
• Weak randomness breaks security
• Difficult to detect misuse
• Older algorithms are broken

11. Stream Cipher Cloud Use Cases
• Video/audio streaming
• VPN tunnels
• Secure messaging
• IoT cloud communication

12. Block Cipher
• Encrypts data in fixed-size blocks
• Common block size: 128 bits
• Same key encrypts each block
• Padding added if needed

13. Block Cipher Working
1.Plaintext divided into blocks
2.Each block encrypted using the key
3.Ciphertext blocks combined
4.Padding applied if required

14. Block Cipher Examples
• AES (industry standard)
• DES ❌ (insecure)
• 3DES ❌ (deprecated)
• Blowfish

15. Modes Of Operation
• Block ciphers require modes:
• ECB ❌ (insecure)
• CBC
• CTR
• GCM ✅ (cloud standard)

16. Why ECB is Insecure
• Same plaintext → same ciphertext
• Reveals patterns
• No randomness
• Not allowed in cloud systems

17. AES-GCM
(CLOUD STANDARD)
Provides:
• Confidentiality
• Integrity
• Authentication
Used in:
• AWS
• Azure
• Google Cloud

18. Advantages Of Block Ciphers
• Strong security guarantees
• Well-studied algorithms
• Resistant to cryptanalysis
• Ideal for data storage

19. Disadvantages Of Block Ciphers
• Slower than stream ciphers
• Requires padding
• More processing overhead
• Complex configuration

20. STREAM vs BLOCK
(COMPARISON TABLE)
Feature Stream Cipher Block Cipher
Data Unit Bit/Byte Fixed block
Speed Very Fast Moderate
Padding No Yes
Security Key Dependent Mode Dependent
Cloud Usage Limited Widely Used

21. Security Comparison
• Stream cipher security depends on keystream
randomness
• Block cipher security depends on mode of operation
• AES-GCM provides strongest cloud security
• Misconfiguration = insecure system

22. Common Misconfigurations
• Using ECB mode
• Reusing keys
• Weak key lengths
• No integrity protection

23. Student Activity
• Identify the correct cipher:
1.Cloud database encryption
2.Live video streaming
3.VPN communication

24. Practical Task
• Encrypt a file using AES-GCM
• Observe:
• Encryption time
• File size
• Ciphertext randomness

25. Summary
• Stream ciphers → speed & real-time
• Block ciphers → security & storage
• AES-GCM dominates cloud security
• Correct configuration is critical