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Security Fundamentals & Crypto · Intermediate

Encapsulating Security Payload (ESP)

IPsec protocol (IP protocol 50) that provides confidentiality, integrity, authentication, and anti-replay.

Definition

ESP encrypts the payload and optionally authenticates it, commonly with AEAD ciphers such as AES-GCM. It works through NAT when encapsulated in UDP 4500 (NAT traversal). ESP is the protocol used by virtually all modern IPsec VPNs.

Example

A packet capture of the VPN shows ESP packets with encrypted payloads and sequence numbers.

Exam tip

ESP is the IPsec choice when confidentiality is required.

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