Introduction to Cybersecurity Lecture 9

Proactive Measures

1. Encryption

What is Cryptography?

• Cryptography secures communication and information by converting plain text into unintelligible cipher text and back into readable text.
• Ensures confidentiality, integrity, authentication, and non-repudiation of data.
• Involves mathematical algorithms for encryption and decryption.
• Encryption transforms plain text into cipher text, while cryptography is the art/science of secret writing.

Encryption vs. Decryption

Process	Encryption	Decryption
Definition	Converts plain text or data into cipher text using an encryption algorithm and a secret key.	Converts cipher text back into plain text using a decryption algorithm and the corresponding secret key.
Purpose	Secures information, making it unreadable to unauthorized parties.	Unlocks encrypted information, making it readable to authorized parties.
Result	Cipher text appears random and unintelligible.	Recovers the original plain text from the cipher text.

Cryptography Terms

• Key: A secret (like a password) used for encryption and decryption.
• Key Management: Includes key generation, distribution, storage, and protection to ensure only authorized access.
• Steganography: Hides information so it is undetectable, differing from encryption, which transforms data visibly.
• Digital Signatures: Provide authentication and non-repudiation by associating unique signatures with electronic documents/messages.

• Cryptographic Hash Functions: Generate fixed-size hash values from data for verifying integrity, password hashing, and digital signatures.

Objectives of Cryptography

1. Confidentiality: Ensures that only authorized individuals can access information, protecting it from unauthorized access throughout its lifecycle.
2. Integrity: Safeguards information from unauthorized alterations, ensuring accuracy and completeness of data.
3. Availability: Guarantees timely and uninterrupted access to information systems for authorized users.
4. Authentication: Verifies the identity of users or entities accessing the system.
5. Non-repudiation: Prevents denial of actions or communications by ensuring that a sender or receiver cannot refute their involvement. Techniques include digital signatures, message authentication codes, and timestamps.

Types of Cryptography

1. Symmetric Key Cryptography

Also known as secret-key cryptography, symmetric encryption uses a single key for both encryption and decryption. The sender and receiver must securely exchange this key, which is a significant challenge.

Pros and Cons of Symmetric Encryption

Pros	Cons
Faster: Utilizes a single key, making execution quicker.	Secure key sharing is challenging and prone to risk.
Identity verification: Uses password authentication for receiver identity proof.	Not scalable for large networks or multiple users.
Easy to execute & manage: Single key simplifies management.

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2. Asymmetric Key Cryptography

Also known as public-key cryptography, asymmetric encryption employs a pair of keys: a public key for encryption and a private key for decryption. The public key is shared openly, while the private key remains confidential to the user.

Pros and Cons of Asymmetric Encryption

Pros	Cons
No issue with distributing keys due to the public-private key pair.	Slower performance compared to symmetric encryption.
Scalable: Easily accommodates communication with multiple parties.	Complex implementation and management due to large key sizes.

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Symmetric vs. Asymmetric Encryption

Aspect	Symmetric Encryption	Asymmetric Encryption
Key Usage	Single shared key for encryption and decryption.	Public-private key pair for encryption and decryption.
Technique Age	An older technique.	A newer technique developed to address symmetric limitations.
Key Sharing	Requires secure key exchange between parties.	Eliminates key sharing by using public-private keys.
Performance	Faster.	Slower due to complex computations.
Scalability	Limited scalability.	Highly scalable for large networks.

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Key Differences Between Symmetric and Asymmetric Encryption

Aspect	Symmetric Encryption	Asymmetric Encryption
Size of Cipher Text	Smaller compared to the original plain text file.	Larger compared to the original plain text file.
Data Size	Suitable for transmitting large amounts of data.	Best for transmitting small data.
Resource Utilization	Low resource usage.	High resource consumption.
Key Lengths	128 or 256-bit key sizes.	RSA 2048-bit or higher key sizes.
Security	Less secure due to the use of a single key for encryption and decryption.	More secure as it uses a public-private key pair.
Number of Keys	Uses a single key for encryption and decryption.	Uses two keys: one for encryption and one for decryption.
Techniques	An older encryption technique.	A modern encryption technique.
Confidentiality	Higher risk of compromise due to a shared key.	No key sharing required, enhancing confidentiality.
Speed	Faster encryption and decryption.	Slower encryption and decryption due to complex computations.
Algorithms	Examples: RC4, AES, DES, 3DES, QUAD.	Examples: RSA, Diffie-Hellman, ECC.

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3. Hash Functions

• Hash functions generate a fixed-length hash value from input data, making it impossible to retrieve the original data from the hash.
• They ensure data integrity by comparing hash values before and after changes.

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Applications of Cryptography

1. Secure Communications

   • Used to encrypt communications between entities, e.g., a web browser and server.

2. End-to-End Encryption (E2EE)

   • Prevents third-party access to data, widely used in messaging systems.
   • Data is encrypted at the sender's end and decrypted only by the intended recipient.

3. Data Storage

   • Ensures secure storage of sensitive data.
   • Example: Office 365 encrypts data during communication and access.

4. Password Storage

   • Protects passwords from being read or hacked when stored in systems.

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Caesar Cipher in Cryptography

• Definition: A substitution cipher that shifts each letter in the plaintext by a fixed number of positions in the alphabet.
• Named After: Julius Caesar, who used it to encrypt messages.
• Mathematical Representation:
  • Transform letters into numbers ($A=0,B=1,...,Z=25$).
  • Apply the formula for encryption: $E(x)=(x+n)\mathrm{mod}26$, where $n$ is the shift value.
  • Decrypt by reversing the shift: $D(x)=(x-n)\mathrm{mod}26$.

Example: Encrypting "HELLO" with a Shift of 3

1. Write the plaintext: HELLO.
2. Apply the shift of 3 to each letter:
   • H -> K
   • E -> H
   • L -> O
   • L -> O
   • O -> R
3. Result: KHOOR.

Decryption

• Reverse the shift (3 positions back): KHOOR -> HELLO.

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Key Characteristics of the Caesar Cipher

• Simple and easy to implement.
• Vulnerable to brute force due to limited key space (only 26 possible shifts).
• Provides basic encryption, suitable for educational purposes or low-security requirements.