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What is Encapsulating Security Payload ?

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  • Difficulty Level : Basic
  • Last Updated : 10 Mar, 2022
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Cyber Security is the branch of computer technology that deals with the security of the virtual cloud and internet. Any information that is stored or transmitted through the cloud needs to be secure and safe. Cyber Networking plays a very important role in maintaining that the connection established is secured and content goes through a secured/ safe channel for transmission.

Security in the network is very important and can’t be compromised in any situation. Security in Networking particularly in IP Sec or IP Network Security is significant and has some characteristics associated with it.

Characteristics Associated with IPSec:

  1. The standardized algorithms present in IP Sec are SHA and MD5.
  2. IPSec uniquely identifies every packet, and then authentication is carried out based on verifying the same uniqueness of the packet.
  3. IP network or IPSec has an ESP present in it for security purposes.

Here, we will discuss ESP, the structure of ESP, and its importance in security.

Encapsulation security payload, also abbreviated as ESP plays a very important role in network security. ESP or Encapsulation security payload is an individual protocol in IPSec. ESP is responsible for the CIA triad of security (Confidentiality, Integrity, Availability), which is considered significant only when encryption is carried along with them. Securing all payload/ packets/ content in IPv4 and IPv6 is the responsibility of ESA.

As the name suggests, it involves encapsulation of the content/ payload encrypts it to suitable form and then there a security check or authentication takes place for payload in IP Network.  Encryption/ encapsulation and security/ authentication make the payload extremely secure and safe from any kind of harm or threat to content/ data/ payload being stolen by any third party. The encryption process is performed by authenticated user, similarly, the decryption process is carried out only when the receiver is verified, thus making the entire process very smooth and secure. The entire encryption that is performed by ESP is carried on the principle of the integrity of payload and not on the typical IP header.

Working of ESP:

  1. Encapsulating Security Payload supports both main Transport layer protocols: IPv4 and IPv6 protocols.
  2. It performs the functioning of encryption in headers of Internet Protocol or in general say, it resides and performs functions in IP Header.
  3. One important thing to note here is that the insertion of ESP is between Internet Protocol and other protocols such as UDP/ TCP/ ICMP.

Modes in ESP:

Encapsulating Security Payload supports two modes, i.e. Transport mode, and tunnel mode.

Tunnel mode:

  1. Mandatory in Gateway, tunnel mode holds utmost importance.
  2. Here, a new IP Header is created which is used as the outer IP Header followed by ESP.

Transport mode:

  1. Here, IP Header is not protected via encryption or authentication, making it vulnerable to threats
  2. Less processing is seen in this mode, so the inclusion of ESP is preferred


Below listed are the advantages of Encapsulating Security Payload:

  1. Encrypting data to provide security
  2. Maintaining a secure gateway for data/ message transmission
  3. Properly authenticating the origin of data
  4. Providing needed data integrity
  5. Maintaining data confidentiality
  6. Helping with antireplay service using authentication header


Below listed are the disadvantages of Encapsulating Security Payload:

  1. There is a restriction on the encryption method to be used
  2. For global use and implementation, weaker encryptions are mandatory to use

Components of ESP:

An important point to note is that authentication and security are not provided for the entire IP packet in transport mode. On the other hand for the tunnel mode, the entire IP packet along with the new packet header is encapsulated.

ESP structure is composed of the following parts as shown below :

ESP Structure

ESP Structure

The diagrammatic representation of ESP has the below-mentioned components :

1. Security Parameter :

  • Security parameters are assigned a size of 32 bits for use
  • Security Parameter is mandatory to security parameter in ESP for security links and associations

2. Sequence Number:

  • The sequence number is 32 bits in size and works as an incremental counter.
  • The first packet has a sequence number 1 assigned to it whenever sent through SA

3. Payload Data:

  • Payload data don’t have fixed size and are variable in size to use
  • It refers to the data/ content that is provided security by the method of encryption

4. Padding:

  • Padding has an assigned size of 0-255 bytes assigned to it.
  • Padding is done to ensure that the payload data which needs to be sent securely fits into the cipher block correctly, so for this padding payloads come to the rescue.

5. Pad Length:

  • Pad Length is assigned the size of 8 bits to use
  • It is a measure of pad bytes that are preceding

6. Next Header:

  • The next header is associated with a size of 8 bits to use
  • It is responsible for determining the data type of payload by studying the first header of the payload

7. Authentication Data:

  • The size associated with authentication data is variable and never fixed for use-case
  • Authentication data is an optional field that is applicable only when SA is selected. It serves the purpose of providing integrity
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