Can someone tell me please if my VPN-configuration is secure enough for small business? (Point to site VPN)

  • IKEv1 Protocol (aggressive mode)
  • PFS/IKE Group: 2 MODP-1024
  • individual PSK for every user
    • 64 Characters (unique)
  • no xauth
  • IPSec over HTTPS disabled
  • IKE-Proposal
    • AES-CBC 256Bit
    • Hash: SHA 512Bit
    • Authentication: Preshared key
  • IPSec Proposal
    • AES-CBC 256
    • Authentication: HMAC-SHA-512
    • AH-Proposal: None

Anything to worry about? How to improve the config? (The Client is Shrewsoft VPN)

  • Which IKEv1 mode is it using (main/base/aggressive?)
    – grawity
    Aug 28, 2019 at 5:21
  • aggressive mode
    – firendlyQuestion
    Aug 28, 2019 at 5:21

1 Answer 1


I don't remember IKEv1 itself being insecure, but it has been superseded by redesigned IKEv2 since 2005, so if the software supports both, I can't think of any advantage to using IKEv1 at all.

Your chosen PFS group (DH 1024-bit) is now considered to be insecure due to its size. The Logjam website claims that currently it's only breakable by "nation states", but that's already not a good sign. These days the minimum bit size for traditional DH seems to be 2048, and recently I've seen recommendations to turn it up to at least 3072 bits. You might even want to use ECDH.

IKEv1 with aggressive mode and PSK authentication is known to be insecure, as it allows attackers to capture the PSK hash and bruteforce the PSK:

But if I recall correctly, IKEv1 main mode does not support using individual PSKs for "roaming" clients as it has no way to distinguish them (except by IP address). So you should use IKEv2 which does support this because each client can send a different initiator ID (rightid).

  • 1
    Also, if correctly set up, IKEv2 can be used with the built-in VPN client on many platforms.
    – Daniel B
    Aug 28, 2019 at 6:22
  • Well... the Windows IKEv2 client seems to be outright impossible to "correctly set up", as it ignores all server-provided routes.
    – grawity
    Aug 28, 2019 at 6:34
  • Yes, that is indeed unfortunate. But routes can be set up, using Add-VpnConnectionRoute. The only shortcoming is that it does not re-dial automatically after interruptions.
    – Daniel B
    Aug 28, 2019 at 7:03
  • That routes even need to be set up is already a shortcoming... I really wanted to replace our current student self-service VPN client with Windows IKEv2, but it'd be going from a short "install this .msi and enter URL" to either a few pages of manual setup, or a custom built provisioning tool / powershell script / .msi that I'd have to maintain, so that's not exactly an improvement either way.
    – grawity
    Aug 28, 2019 at 7:07
  • As far as I understand the "aggressive mode and PSK" problem is only relevant with a short PSK or a weak hash. I'm using a 64 char PSK and I just switched to SHA-512.This should be secure enough, even with aggressiv mode? Aug 28, 2019 at 9:32

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