Which of the following is the most reliable authentication method for remote access?

Question

Options

• AVariable callback system
• BSynchronous token
• CFixed callback system
• DCombination of callback and caller ID

• A
  4% (1)
• B
  87% (20)
• D
  9% (2)

Explanation

Synchronous tokens (like TOTP/RSA SecurID) generate time-based one-time passwords that are valid for only a short window, making them highly reliable for remote access - a stolen code is useless seconds later, and replay attacks are effectively eliminated since the server and token stay clock-synchronized.

Option A (Variable callback) lets the user specify any callback number, which an attacker can exploit by supplying their own number - defeating the purpose of the callback entirely. Option C (Fixed callback) is more secure than variable, but call-forwarding and PSTN vulnerabilities mean it can still be circumvented without verifying the actual identity of the person answering. Option D (Callback + caller ID) sounds stronger but caller ID is trivially spoofed, so combining a weak control with an easily faked one does not produce a reliable system.

Memory tip: Think "sync = secure" - a synchronous token requires both sides (you and the server) to agree on time, making it self-validating without relying on external phone infrastructure that can be forwarded, spoofed, or social-engineered.

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