IPsec (Internet Protocol Security) is a suite of protocols designed to secure Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. IPsec includes protocols for establishing mutual authentication between agents at the beginning of a session and negotiation of cryptographic keys to be used during the session. It is widely used in virtual private networks (VPNs), where it provides a secure tunnel for the exchange of data between networks over an untrusted network, typically the internet.
IPsec operates in two modes:
Transport Mode: In transport mode, IPsec encrypts only the payload of the IP packet, not the IP header. It's typically used for end-to-end communication between two devices, such as two computers or a computer and a server.
Tunnel Mode: In tunnel mode, IPsec encrypts both the payload and the header of the IP packet. This mode is used to create a secure "tunnel" between two networks, such as between two corporate offices over the internet, allowing for secure communications between networks.
Key components of IPsec include:
- IKE (Internet Key Exchange): IKE is used to set up a shared security policy and authenticated keys between two parties. IKE establishes an IPsec connection using a process that typically involves exchanging keys and agreeing on encryption methods.
- AH (Authentication Header): AH provides data integrity, data origin authentication, and an optional anti-replay service. It authenticates the IP packet but does not encrypt it.
- ESP (Encapsulating Security Payload): ESP provides confidentiality, data-origin authentication, integrity, and an optional anti-replay service. It encrypts the data being sent for confidentiality and also provides limited authentication.
IPsec is versatile and can be used in a wide range of applications, from securing remote access to a corporate network over the internet to securing data exchange between servers and clients or between routers in different segments of a network. It's a critical technology for ensuring secure communications over potentially insecure networks like the internet.