IKE/IPsec Extended Sequence Number (ESN) supportĦ4-bit Extended Sequence numbers (as described in RFC 4303, RFC 4304 as an addition to IKEv1, and RFC 5996 for IKEv2.) are supported for IPsec when Replay Detection is enabled. If any encrypted packets arrive out of order, the FortiGate unit discards them. Replay Detection enables the FortiGate unit to check all IPsec packets to see if they have been received before. IPsec tunnels can be vulnerable to replay attacks. The keys are generated automatically using a Diffie-Hellman algorithm. The Phase 2 Proposal parameters select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of Security Associations (SAs). In Phase 2, the VPN peer or client and the FortiGate unit exchange keys again to establish a secure communication channel.
#Diffie hellman setting fortinet vpn manual
The information and procedures in this section do not apply to VPN peers that perform negotiations using manual keys. When defining Phase 2 parameters, you can choose any set of Phase 1 parameters to set up a secure connection and authenticate the remote peer.įor more information on Phase 2 settings in the web-based manager, see IPsec VPN in the web-based manager on page 38. The basic Phase 2 settings associate IPsec Phase 2 parameters with a Phase 1 configuration. Phase 2 parameters define the algorithms that the FortiGate unit can use to encrypt and transfer data for the remainder of the session. The following topics are included in this section:Ĭonfiguring the Phase 2 parameters Phase 2 settingsĪfter IPsec VPN Phase 1 negotiations complete successfully, Phase 2 negotiation begins. If the Diffie-Hellman group is not set to 14 or larger, this is a finding.Ĭonfigure the VPN gateway to ensure Diffie-Hellman Group 14 or larger is used.This section describes the Phase 2 parameters that are required to establish communication through a VPN. Group 1 is the default for many VPN gateways. If the group has not been configured, determine what the default for the VPN gateway is or enter the appropriate show command to display the policies. Verify Group 14 or larger has been configured. IPSec VPN Gateway Security Technical Implementation GuideĮxamine all ISAKMP policies configured on the VPN gateway to determine what Diffie-Hellman group is being used. Hence, the larger the modulus, the more secure the generated key is considered to be. The security of the DH key exchange is based on the difficulty of solving the discrete logarithm in which the key was derived from. DH group 1 consists of a 768 bit modulus, group 2 consists of 1024 bit modulus, group 5 uses a 1536 bit modulus, and group 14 uses a 2048 bit modulus. DH public key cryptography is used by all major VPN gateways. The DH group is configured as part of the IKE Phase 1 key exchange settings. The peers produce the same shared secret by using each other’s public key and their own private key using the DH algorithm. The process works by two peers both generating a private and a public key and then exchanging their public keys with each other.
IKE uses DH to create keys used to encrypt both the Internet Key Exchange (IKE) and IPsec communication channels. Diffie-Hellman (DH) is a public-key cryptography scheme that allows two parties to establish a shared secret over an insecure communications channel.
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