INTRODUCTION TO VPN

By: Sameh El-HakimCyber Security Engineer

TYPES OF VPN

Client VPN: Home or rooming users to an office.

Site-to-site: Connect remote offices to a main office.

IPSEC: IP SECURITY

Is a suite of protocols, standards, and algorithms to secure traffic over an untrusted network.

Provide 3 Core Services:

CONFIDENTIALITY & ENCRYPTION Symmetric key Asymmetric key

DIFFIE–HELLMAN KEY EXCHANGEThe Diffie-Hellman key exchange is a public-key technology. It is (by itself) not an encryption algorithm (or signature algorithm).

DIFFIE-HELLMAN GROUPS

Public key use encryption algorithms to encrypt the data:DES3DESAESBlowfish

DH Group: Used to determine the strength of the key:DH Group 1: 768-bit groupDH Group 2: 1024-bit groupDH Group 5: 1536-bit groupDH Group 14: 2048-bit groupDH Group 15: 3072-bit groupDH Group 19: 256-bit elliptic curve groupDH Group 20: 384-bit elliptic curve group

DATA INTEGRITY AND HASHING Hashed message authentication code “HMAC” is used to perform this hashing function.

HMAC Algorithms: HMAC-MD5: 128 bit hashed key.

HMAC-SHA1: 160 bit hashed key.

AUTHENTICATION

Use either: Pre-shared keys: a secret string of text is used on each device to authenticate each other. This string must be pre-agreed upon and identical in each device. This string is then hashed into a digital signature.

RSA Digital Signature: a CA is used to apply a verified digital signature.

CERTIFICATE AUTHORITY

Certificate authority: A client creates a blank or unsigned certificate and sends it to can including the clients ID. This communication secured using DH private/public key exchange.

CA computes an encrypted hash. The certificate is now signed with the CA’s digital signature and the it sent back to the client.

The client then send the signed certificate, along with its keys, to any VPN peers.

Vendors:VerisignGodaddyEnTrust

IPSEC PROTOCOLS

AUTHENTICATION HEADER “AH” Only provides both authentication and integrity because it doesn’t encrypt the packet.

It compute a hash value on both the payload and the header of the packet.

It will not work through a NATed devices because NATing changes the IP header of a packet during translation.

ENCAPSULATION SECURITY PAYLOAD “ESP” Provides CIA but the hash doesn’t include the IP header of the packet ESP work on a NATed devices

Add additional header and tail to a packet.

TRANSPORT VS TUNNEL MODES Transport mode: No edits on the IP header.

Used in securing communication from on device to another.

Tunnel mode: the entire packet is hashed or encrypted a temporary IP header is applied to the packet during transit Used to tunnel traffic from one site to another.

SECURITY ASSOCIATIONS AND ISAKMP

SA is a collection of parameters required to establish a secure session

SA is unidirectional, two SA required for a bidirectional communication, a single SA can be used for AH or ESP, but not both, must create two or more SA for each direction if using both AH and ESP

Security Association Database ( SAD) ,  Security Policy Database (SPD)

ISAKMP is internet security association and key management protocol, used for establishing security associations and cryptographic keys, only provides the framework for authentication and key exchange, but key exchange independent.

INTERNET KEY EXCHANGE (IKE) Used for establishing IPSEC sessions

Five variation of an IKE negotiation, two modes (aggressive and main modes)

Three authentication methods (pre-shared, public key encryption and public key signature)

IKE – PHASE 1

Establish the initial tunnel and negotiate and keys are exchanged based on the IKE policy sets.

Two Modes: Main Mode & aggressive mode

- IKE Policy sets are created to negotiate several parameters:

1- DH group: determine the key length & create it

2- Encryption Algorithms: DES, 3DES, AES

3- Hashing Algorithms: MD5, SHA-1

4- Authentication method: pre-shared key or RSA signature

5- SA lifetime

IKE – PHASE 2

Establish the IPSEC tunnel “IPSEC SA”, negotiate parameters for the data traversing that tunnel

These parameters are contained in an IPSEC transform set:1- DH group: determine the key length & create it

2- Encryption Algorithms: DES, 3DES, AES

3- Hashing Algorithms: MD5, SHA-1

4- Authentication method: pre-shared key or RSA signature

5- SA lifetime

THE FIVE STEPS OF IPSEC

STEP 1- DEFINING INTERESTING TRAFFIC Using ACL

STEP 2 - IKE PHASE 1

STEP 3 - IKE PHASE 2

The purpose of IKE phase 2 is to negotiate IPSec SAs to set up the IPSec tunnel. IKE phase 2 performs the following functions:

Negotiates IPSec SA parameters protected by an existing IKE SA Establishes IPSec security associations Periodically renegotiates IPSec SAs to ensure security Optionally performs an additional Diffie-Hellman exchange

IKE phase 2 has one mode, called quick mode. Quick mode occurs after IKE has established the secure tunnel in phase 1. It negotiates a shared IPSec policy, derives shared secret keying material used for the IPSec security algorithms, and establishes IPSec SAs. Quick mode exchanges nonces that provide replay protection. The nonces are used to generate new shared secret key material and prevent replay attacks from generating bogus SAs.

Quick mode is also used to renegotiate a new IPSec SA when the IPSec SA lifetime expires. Base quick mode is used to refresh the keying material used to create the shared secret key based on the keying material derived from the Diffie-Hellman exchange in phase 1.

STEP 4 - IPSEC ENCRYPTED TUNNEL

STEP 5 - TUNNEL TERMINATION

REFERENCES

THANK YOU