Westermo RedFox Series - Manual (Page 794)

Westermo OS Management Guide
Version 4.17.0-0
These Diffie-Hellman key exchange groups are supported and are config-
urable for both IKE and ESP (for PFS) individually.
When using IKE main mode, Alice and Bob can be configured to automatically
negotiate a suitable cipher suite. When using aggressive mode, Alice and Bob
should be configured to use a specific cipher suite (same at both sides). When
aggressive mode is selected, WeOS by default uses the suite AES128-SHA1-
DH1024.
35.1.3 Perfect Forward Secrecy
Perfect Forward Secrecy (PFS) refers to the property that if an ESP session key
is compromised, the attacker will only get access to the data protected by that
single key. Previous and later session keys will not be revealed just because that
single key was compromised, thus data encrypted by those keys is still protected.
Note
This setting is not supported by all IPsec implementations. It is however
recommended to have it enabled, on both sides of the connection.
PFS uses Diffie-Hellman to exchange new session keys. The Diffie-Hellman group
can be automatically selected or manually configured.
PFS with automatic Diffie-Hellman group selection is enabled by default on all
new tunnels.
If you are unsure what do to, you can safely disable PFS. If the IPsec daemon
receives a request with PFS, it will allow it despite PFS being disabled or not.
35.1.4 Data encapsulation and encryption
IPsec specifies two modes to encapsulate the data, a transport and a tunnel
mode. WeOS IPsec VPN only supports the tunnel mode. In the tunnel mode,
the original IP packets are encapsulated within another IP packet as shown in
fig. 35.4 .
In IPsec there is also the choice by protecting the data using AH (Authentication
Header), and ESP (Encapsulating Security Payload) formats. WeOS only supports
ESP, which is the format to use to achieve both data encryption and integrity
protection.
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