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Understanding Confidentiality in Symmetric Encryption and Traffic Analysis

This chapter explores the importance of confidentiality in cryptography, specifically focusing on symmetric encryption and traffic analysis. It discusses the monitoring of communication flows, the use of encryption to obscure header information, and the impact of traffic volumes on security visibility. The chapter also details key distribution methods between parties, including physical delivery and third-party relays, alongside the hierarchy of keys typically used in secure systems. Additionally, it covers the role of random numbers and pseudorandom number generators (PRNGs) in cryptography.

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Understanding Confidentiality in Symmetric Encryption and Traffic Analysis

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  1. CPSC 3730 Cryptography Chapter 7 Confidentiality UsingSymmetric Encryption Cryptography

  2. Traffic Analysis • is monitoring of communications flows between parties • useful both in military & commercial spheres • can also be used to create a covert channel • link encryption obscures header details • but overall traffic volumes in networks and at end-points is still visible • traffic padding can further obscure flows • but at cost of continuous traffic Cryptography

  3. Fig. 7.6 Traffic Padding Encryption Device Cryptography

  4. Key Distribution • symmetric schemes require both parties to share a common secret key • issue is how to securely distribute this key • often secure system failure due to a break in the key distribution scheme Cryptography

  5. Key Distribution • given parties A and B have various key distribution alternatives: • A can select key and physically deliver to B • third party can select & deliver key to A & B • if A & B have communicated previously can use previous key to encrypt a new key • if A & B have secure communications with a third party C, C can relay key between A & B Cryptography

  6. Key Hierarchy • typically have a hierarchy of keys • session key • temporary key • used for encryption of data between users • for one logical session then discarded • master key • used to encrypt session keys • shared by user & key distribution center Cryptography

  7. Key Distribution Scenario Cryptography

  8. Key Distribution Issues • hierarchies of KDC’s required for large networks, but must trust each other • session key lifetimes should be limited for greater security • use of automatic key distribution on behalf of users, but must trust system • use of decentralized key distribution • controlling key usage Cryptography

  9. Random Numbers • many uses of random numbers in cryptography • nonces in authentication protocols to prevent replay • session keys • public key generation • keystream for a one-time pad • in all cases its critical that these values be • statistically random, uniform distribution, independent • unpredictability of future values from previous values Cryptography

  10. Pseudorandom Number Generators (PRNGs) • often use deterministic algorithmic techniques to create “random numbers” • although are not truly random • can pass many tests of “randomness” • known as “pseudorandom numbers” • created by “Pseudorandom Number Generators (PRNGs)” Cryptography

  11. ANSI X9.17 PRG Cryptography

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