Cybersecurity Essentials Lecture Two

What is Security of Data Model?

The OSI security architecture provides a structured approach to implementing and managing security. Developed as an international standard, it helps vendors align their security features to meet defined services and mechanisms.

Threat, Vulnerability, Attack

• Threat: Any event or circumstance with the potential to negatively impact organizations or individuals through unauthorized access, disclosure, modification, destruction, or denial of service.
• Vulnerability: A system weakness that can be exploited to cause harm.
• Attack (Incident): Occurs when a threat exploits a vulnerability.
• Countermeasure (Control): Actions that reduce threats or vulnerabilities, aiming to prevent, deflect, or respond to attacks.

Security Attacks

• Passive Attacks: Attempt to gain information without affecting system resources.
• Active Attacks: Aim to alter system resources or disrupt operations.

Security Services

Security services support requirements such as:

• Confidentiality
• Integrity
• Availability
• Authenticity
• Access Control
• Non-repudiation

They are implemented via specific security mechanisms.

Security Mechanisms

• Cryptographic Algorithms:
  • Reversible: Encryption algorithms for encryption and decryption.
  • Irreversible: Hash functions and message authentication codes (e.g., digital signatures).
• Data Integrity: Ensures data remains unchanged.
• Digital Signature: Verifies source and integrity of data.
• Authentication Exchange: Confirms identity through information exchange.
• Traffic Padding: Obscures patterns in data transmission.
• Routing Control: Chooses secure transmission paths.
• Notarization: Uses a trusted third party to verify data exchange properties.
• Access Control: Enforces access permissions.

Cryptography

Cryptography is the mathematical science of securing data through transformation. It's vital for ensuring safe communication and data storage.

Cryptographic Algorithms

• Keyless Algorithms: Do not use keys; includes hash functions and pseudorandom number generators.
• Single-Key Algorithms: Use one secret key for encryption and decryption.
• Two-Key Algorithms: Use a pair of related keys — a public key and a private key.

Keyless Algorithms

Used for integrity and verification. Main types include:

• Cryptographic Hash Functions: Convert variable-length data into a fixed-size output (digest).
  • Properties:
    1. Same input gives the same output.
    2. Fixed output length.
    3. Fast computation.
    4. Unpredictable and non-reversible.
    5. Collision-resistant.
  • Common Algorithms:
    • Secure Hash Algorithms (SHA-0, SHA-1, SHA-2, SHA-3)
    • Message Digest (MD2, MD4, MD5, MD6)
• Pseudorandom Number Generators: Produce seemingly random, deterministic sequences.

SHA-1 (Secure Hash Algorithm 1)

SHA-1 produces a 160-bit (20-byte) message digest from input data, typically displayed as a 40-character hexadecimal number.

SHA-1 Logic Operations

a	b	!a	a&b	a|b	a^b
0	0	1	0	0	0
0	1	1	0	1	1
1	0	0	0	1	1
1	1	0	1	1	0

• Right Shift (>>): Shifts bits right, discards least significant bits.
• Left Shift (<<): Shifts bits left, fills with zeroes.

Example: Encrypting "hi" using SHA-1

1. ASCII Conversion: Convert each character to ASCII (h -> 104, i -> 105).
2. Binary Conversion: Convert ASCII to 8-bit binary (104 -> 01101000, 105 -> 01101001).
3. Combine Binary: Concatenate binary bits (0110100001101001, 16 bits).
4. Append 1: Add a single 1 bit (01101000011010011, 17 bits).
5. Pad with Zeros: Add 0s to reach 448 bits.
6. Append Length: Add 64-bit binary representation of original length (16) to form a 512-bit chunk.
7. Split into Words: Divide 512-bit chunk into 16 words (32 bits each).
8. Extend Words: Expand 16 words to 80 words using XOR operations (e.g., $W16=W13\oplus W8\oplus W2\oplus W0$).
9. Initialize Constants:
   • h0 = 01100111010001010010001100000001 (A = h0)
   • h1 = 11101111110011011010101110001001 (B = h1)
   • h2 = 10011000101110101101110011111110 (C = h2)
   • h3 = 00010000001100100101010001110110 (D = h3)
   • h4 = 11000011110100101110000111110000 (E = h4)
10. Process 80 Words in 4 Functions (20 words each):
    • Function 1 (W0–W19):
      • $F=(B\wedge C)\vee (\mathrm{\neg }B\wedge D)$
      • $K=01011010100000100111100110011001$
      • $Temp=(A<<5)+F+K+E+W_i$
      • Truncate Temp to 32 bits
      • Update: $E=D$, $D=C$, $C=B<<30$, $B=A$, $A=Temp$
    • Function 2 (W20–W39):
      • $F=B\oplus C\oplus D$
      • $K=01011010100000100111100110011001$
      • Same Temp and update steps
    • Function 3 (W40–W59):
      • $F=(B\wedge C)\vee (B\wedge D)\vee (C\wedge D)$
      • K = 01011010100000100111100110011001
      • Same Temp and update steps
    • Function 4 (W60–W79):
      • $F=B\oplus C\oplus D$
      • $K=11001010011000101100000111010110$
      • Same Temp and update steps
11. Final Hash:
    • Compute: $h0+=A$, $h1+=B$, $h2+=C$, $h3+=D$, $h4+=E$
    • Truncate each to 32 bits
    • Convert to hexadecimal
12. Output: Concatenate h0, h1, h2, h3, h4 as the final SHA-1 hash.