Imagine a scenario where a company needs to securely transmit highly confidential financial reports to its remote employees. To ensure the confidentiality, authenticity, and integrity of these reports during transmission, you will explore the roles of various cryptographic primitives.

1. Role of Symmetric-key Cryptography:
   1. How would symmetric-key encryption be applied to the financial reports?
   2. What are the key management challenges in distributing the symmetric key to all authorized remote employees, and how might these be addressed?
   3. Discuss its primary advantages (e.g., speed, efficiency) and disadvantages (e.g., key distribution) in this specific context.
2. Role of Public-key Cryptography:
   1. How can public-key encryption be used to securely exchange the symmetric key mentioned above?
   2. How would digital signatures, a component of public-key cryptography, be used to ensure the authenticity and integrity of the reports and the sender?
   3. Discuss its primary advantages (e.g., secure key exchange, non-repudiation) and disadvantages (e.g., computational overhead) in this specific context.
3. Role of Cryptographic Hashing:
   1. Explain how a cryptographic hash function would be used to verify the integrity of the financial reports after transmission.
   2. What happens if the computed hash of the received report does not match the original hash, and what does this imply?
   3. Discuss its primary advantages (e.g., integrity verification, efficiency) and potential limitations (e.g., lack of confidentiality) in this specific context.
4. Combined Approach:
   1. Propose a comprehensive solution that leverages the strengths of all three cryptographic primitives (symmetric-key, public-key, and hashing) to achieve confidentiality, authenticity, and integrity for the financial reports.
   2. Illustrate the step-by-step process of how a report would be prepared, transmitted, and received using this combined approach.
   3. Discuss how this integrated solution mitigates the individual weaknesses of each primitive.

Role of Symmetric-key Cryptography

1. Application to Financial Reports

   1. Symmetric-key encryption (e.g., AES-256) would be used to encrypt the entire contents of the financial report. This ensures confidentiality by transforming readable data (plaintext) into an unreadable format (ciphertext) using a shared secret key.

   2. For example, the company encrypts the report with a symmetric key K, and the ciphertext is what gets transmitted to remote employees.

   3. Key Management Challenges & Solutions

      1. Key distribution is the Achilles' heel of symmetric cryptography:
      2. Challenges:
         1. Secure distribution of the key K to all authorized remote employees.
         2. Ensuring only authorized individuals can access K.
         3. Risk of interception or leakage during distribution.
      3. Solutions:
         1. Use Public-Key Cryptography (asymmetric encryption) to encrypt the symmetric key per recipient.
         2. Implement Key Management Systems (KMS) to automate and securely manage key lifecycle (generation, rotation, revocation).
         3. Use Pre-shared keys (PSK) only in small, controlled environments (not scalable).

   4. Advantages & Disadvantages in Context

      Advantages	Disadvantages
      Fast and efficient for encrypting large files like financial reports.	Key distribution becomes complex at scale.
      Low computational overhead – good for real-time systems.	All recipients share the same key, increasing risk of exposure.
      Relatively simple to implement.	No built-in mechanism for authenticity or non-repudiation.

Role of Public-key Cryptography

1. Secure Symmetric Key Exchange

   1. Public-key cryptography (e.g., RSA, ECC) can be used to encrypt the symmetric key (K) for each remote employee.
   2. How:
      1. Each employee has a public-private key pair.
      2. The company encrypts K using the employee’s public key.
      3. Only the corresponding private key (known only to the employee) can decrypt K.
      4. This ensures confidential delivery of the symmetric key without needing a secure channel.
   3. Use of Digital Signatures
      1. Digital signatures ensure authenticity and integrity:
      2. How:
         1. The company computes a hash of the report (e.g., SHA-256).
         2. It then signs the hash with its private key.
         3. This signature is sent along with the encrypted report.
         4. Employees use the company’s public key to verify the signature.
         5. If the signature is valid:
            1. The report hasn’t been altered (integrity).
            2. The report is genuinely from the company (authenticity).
            3. The company cannot deny sending it (non-repudiation).

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2. Advantages & Disadvantages in Context

   Advantages	Disadvantages
   Enables secure key exchange over insecure networks.	Slower and more computationally intensive than symmetric encryption.
   Supports non-repudiation and digital signatures.	Inefficient for encrypting large files directly.
   Scales better for key management in large organizations.	Requires a robust Public Key Infrastructure (PKI).