User A is writing a sensitive email message to user B outside the local network. User A has chosen to use PKI to secure his message and ensure only user B can read the sensitive email. At what layer…

Question

Options

• AApplication
• BTransport
• CSession
• DPresentation

• A
  4% (1)
• C
  4% (1)
• D
  91% (21)

Explanation

OSI Encryption at the Presentation Layer

Option D (Presentation) is correct because the Presentation Layer (Layer 6) is specifically responsible for data formatting, translation, and encryption/decryption - it acts as the "translator" between the application and the rest of the network, ensuring data is in a readable and secure format before transmission.

Why the distractors are wrong:

• Application Layer (A) handles user-facing protocols like SMTP or HTTP that initiate the email process, but not the actual encryption/decryption mechanics
• Transport Layer (B) manages end-to-end communication and reliability (e.g., TCP/UDP), not encryption - though SSL/TLS operates here in practice, the conceptual OSI answer points to Presentation
• Session Layer (C) manages establishing, maintaining, and terminating communication sessions between devices - it has no encryption responsibility

Memory Tip: Think of the Presentation layer as a Privacy screen - it Prepares data by encrypting it before sending and decrypting it upon receipt. Remember: "Presentation = Pretty (secure) data" - it makes data presentable and private!

Exam Note: While real-world PKI encryption often occurs at the Transport Layer, OSI model exam questions follow the theoretical model where encryption belongs to the Presentation Layer.

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