5 cybersecurity - cryptography

1. Cryptography Overview

  • Definition: Encryption, or cryptography, refers to secret writing, serving as a primary defense in computer security.

  • Purpose: Protects data from unauthorized access, ensuring confidentiality against reading, modifying, or fabricating data.

2. Problems Addressed by Encryption

  • Context of Use: Though often described through sending secret messages, encryption also protects files and sensitive information in memory.

  • Scope: It focuses on securing any digital object for authorized access only.

3. Message Transmission Example

Steps Involved:

  • Participants:

    • S: Sender

    • T: Transmission medium

    • R: Recipient

    • O: Interceptor or intruder

  • Transmission Vulnerability: Message sent from S via T to R is susceptible to various attacks by O.

4. Attacks on Message Confidentiality

Possible Attacks by an Attacker:

  • Blocking: Prevents the message from reaching R, affecting its availability.

  • Intercepting: Reads or listens to the message, compromising confidentiality.

  • Modifying: Alters the message, affecting integrity.

  • Fabricating: Creates a counterfeit message imitating S, undermining integrity.

Conclusion

  • Role of Encryption: Essential for maintaining secure data in insecure environments.

5. Encryption Terminology

  • Encoding and Decoding:

    • Encryption: Process of encoding a message (C = E(P)).

    • Decryption: Reverse process of converting encrypted message back to original (P = D(C)).

  • Term Variations: "Encode/Decode" and "Encipher/Decipher" are alternative terms.

  • Cryptosystem: Framework for encryption and decryption processes.

  • Plaintext & Ciphertext: Original message vs. encrypted message.

6. Encryption Keys

  • Cryptosystem Components: Rules and algorithms for encryption/decryption.

  • Key Usage: Defines the relationship between plaintext and resulting ciphertext (C = E(K, P)).

  • Keyless Ciphers: Use encryption schemes without keys.

7. Key Types

Symmetric Encryption:

  • Key Characteristics: Same key used for both encryption and decryption, resulting in C = D(K, E(K, P)).

Asymmetric Encryption:

  • Key Pair Usage: Separate keys for encryption (KE) and decryption (KD), allowing P = D(KD, E(KE, P)).

8. Historical Figure

  • Claude Shannon: Recognized as the father of modern cryptography, established a mathematical foundation for information security.

9. Cryptanalysis

  • Purpose: Investigating cryptographic systems for vulnerabilities.

  • Materials Used: Encrypted messages, known algorithms, intercepted data, and statistical tools.

10. Work Factor

  • Definition: Refers to the effort needed to break an encryption.

  • Adequacy: An encryption method is considered secure if the effort to decrypt is greater than the value of the data encrypted.

11. Symmetric and Asymmetric Encryption

Symmetric:

  • Key Sharing: Users A and B share a single secret key for both encryption and decryption.

Asymmetric:

  • Key Generation: Each user has a publicly shared key and a secret private key, allowing secure communications.

12. Encryption Algorithms: Stream vs. Block Ciphers

Stream Ciphers:

  • Functionality: Encrypts data bit-by-bit or byte-by-byte; ideal for real-time applications.

Block Ciphers:

  • Functionality: Encrypts a block of data at once; more efficient for large data sets.

13. Advanced Encryption Standards (AES) and Data Encryption Standard (DES)

DES:

  • Details: A symmetric block cipher utilizing a 56-bit key.

  • Structure: Involves 16 cycles of substitutions and permutations for security.

AES:

  • Adoption: Selected by NIST in 2001, known for efficiency and strong security; supports keys of varied lengths (128, 192, 256 bits).

14. Public Key Cryptography

  • Introduction: Introduced by Whitfield Diffie and Martin Hellman in 1976.

  • Structure: Comprises two keys—public and private; enables secure communication without a shared secret key.

15. Key Exchange and Authentication

Protocols:

  • Key Exchange: Securing communication through public key transmission.

  • Authentication: Ensures sender authenticity utilizing digital signatures and hash functions.

16. Certificates

  • Definition: A public key bound to a verified identity, ensuring trust in communications.

  • Certificate Authorities: Entities that verify identities before issuing certificates.

17. Summary of Tools

Cryptographic Functions:

  • Secret Key: Protects confidentiality and integrity of data.

  • Public Key: Used for key exchange and verification.

  • Error Detection Codes: Identifies and corrects data transmission errors.

18. Conclusion

  • Access Control: Users authenticate based on knowledge, identity, or possession; systematic encryption protects against unauthorized access and data manipulation.