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Security Fundamentals & Crypto · Intermediate

Out-of-Band Key Exchange

Delivering keys through a separate channel from the one the keys will protect.

Definition

Out-of-band exchange prevents an attacker who controls the data channel from intercepting the key. Methods include courier, separate phone calls, physical media, or in-person ceremonies. It is common for pre-shared keys and initial trust establishment.

Example

A VPN pre-shared key is read aloud over a phone call instead of emailed with the configuration.

Exam tip

In-band exchange uses the same channel and must be protected by asymmetric crypto.

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