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- 2072 Kartik · 4 marks
- 2070 Asar · 4 marks
Short note: IPSec
Short answer
IPsec provides network-layer security with AH for authentication, ESP for encryption, and IKE for key management. It operates in transport mode (host-host) or tunnel mode (gateway VPN), protecting entire IP packets transparently to applications.
Write a short note on IPSec.
IPsec (IP Security) is a suite of protocols (RFC 4301) that provides security at the network layer, protecting IP packets by authentication, integrity and encryption. It works for both IPv4 and IPv6 and is transparent to applications, so one mechanism protects all upper-layer traffic. It is the basis of many VPNs.
Components
- AH (Authentication Header, protocol 51): gives data origin authentication, integrity and replay protection; no encryption.
- ESP (Encapsulating Security Payload, protocol 50): gives confidentiality (encryption) plus optional authentication and integrity.
- IKE (Internet Key Exchange): negotiates keys and algorithms and sets up Security Associations (SA). An SA is a one-way logical connection identified by SPI, destination address and protocol.
Modes
Transport mode: [IP hdr][ESP hdr][ TCP + data ][ESP trailer]
Tunnel mode : [New IP][ESP hdr][ old IP hdr + TCP + data ][trailer]
| Mode | Protects | Use |
|---|---|---|
| Transport | Payload only; original IP header kept | Host to host |
| Tunnel | Entire original packet inside a new IP packet | Gateway to gateway (VPN) |
Algorithms
Encryption: AES, 3DES. Integrity: HMAC-SHA. Key exchange: Diffie-Hellman.
✓ Answer checked by Claude Opus 5.5 (high effort)