IPSec (ESP, AH, DES, MD5, SHA, DH)

Internet Protocol security (IPSec) is a framework of open standards for helping to ensure private, secure communications over Internet Protocol (IP) networks through the use of cryptographic security services. IPSec supports network-level data integrity, data confidentiality, data origin authentication, and replay protection. Because IPSec is integrated at the Internet layer (layer 3), it provides security for almost all protocols in the TCP/IP suite, and because IPSec is applied transparently to applications, there is no need to configure separate security for each application that uses TCP/IP.
The examples of IPsec are ESP, AH, DES, MD5, SHA, and DH.

IPSec helps provide defense-in-depth against:
• Network-based attacks from untrusted computers, attacks that can result in the denial-of-service of applications, services, or the network
• Data corruption
• Data theft
• User-credential theft
• Administrative control of servers, other computers, and the network.

Authentication Headers (AH)
AH provides connectionless integrity and data origin authentication for IP datagrams and provides protection against replay attacks.
Encapsulating Security Payloads (ESP)
ESP provide confidentiality, data-origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and limited traffic-flow confidentiality.

Data Encryption Standard(DES)
DES is a widely-used method of data encryption using a private (secret) key . DES applies a 56-bit key to each 64-bit block of data. The process can run in several modes and involves 16 rounds or operations.
Message Digest 5(MD5)
MD5 is a widely used cryptographic hash function with a 128-bit hash value. MD5 is widely used in security-related applications, and is also frequently used to check the integrity of files. MD5 value of file is considered to be a highly reliable fingerprint that can be used to verify the integrity of the file's contents. If as little as a single bit value in the file is modified, the MD5 value for the file will completely change. Forgery of a file in a way that causes MD5 to generate the same result as that for the original file is considered to be extremely difficult.
SHA
The Secure Hash Algorithm is one of a number of cryptographic hash functions published by the National Institute of Standards and Technology (NIST) as a U.S. Federal Information Processing Standard (FIPS):
Diffie-Hellman(DH)
The protocol has two system parameters p and g. They are both public and may be used by all the users in a system. Parameter p is a prime number and parameter g (usually called a generator) is an integer less than p, which is capable of generating every element from 1 to p-1 when multiplied by itself a certain number of times, modulo the prime p. However, it is vulnerable to a middleperson attack.
Security Associations (SA)
SA provides the bundle of algorithms and data that provide the parameters necessary to operate the AH and/or ESP operations. The Internet Security Association and Key Management Protocol (ISAKMP) provides a framework for authentication and key exchange, with actual authenticated keying material provided either by manual configuration with pre-shared keys, Internet Key Exchange (IKE and IKEv2), Kerberized Internet Negotiation of Keys (KINK), or IPSECKEY DNS records.