IPsec VPN - which encryption?

Hi

We have a Fortigate in HQ connected to a bunch of branch offices with IPsec VPN in a hub & spoke configuration.
Speeds varies from 10mbps to 100 mbps pr. Branch office.
Currently phase2 is set up with: aes128 and SHA256.

Fortigate now supports AES GCM and can be used in phase2 for IPsec VPN tunnels.

There something new & fancy out there, but I have no idea if it's better.
Hope some of you in here can enlighten me :)

1. Does GCM provide better throughput and/or is less CPU intensive?
2. Does it provide better security?

Understand the principle of encryption but not the inner workings, please take that into consideration.

Regards.
LenblockAsked:
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JohnBusiness Consultant (Owner)Commented:
A VPN tunnel usually delivers the slow side of an ADSL link. You are probably getting the speed (10 Mbits/sec) that you can. The type of encryption affects security but not speed so much. Your encryption looks fine.

I have not yet used AES GCM so cannot comment on that part.
gheistCommented:
Last time I measured it was 2-3Gbps with AES+SHA2 per AES-NI CPU core, well in excess of your needs. There is no weaknesses solved by bigger encryption blocks, small ones should be fine too if you can measure speed difference (you need at least 10GbE network to saturate CPU)
btanExec ConsultantCommented:
GCM is a more secure option compared to CBC used for block chaining in AES. It provides both confidentiality and data origin authentication. It can add in overheads but ill work pretty nice if your hardware can accelerate AES e.g. via the AES-NI instruction set. It is a good choice because it encrypts and authenticates packets at the same time. Its implementation allows pipelining which the older CBC chaining does not allows and may even stall if attempted to do pipeline execution.

http://help.fortinet.com/fos50hlp/54/Content/FortiOS/fortigate-ipsecvpn-54/IPsec_VPN_Concepts/Encryption.htm

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LenblockAuthor Commented:
We do have accelerator for IPsec traffic in our HUB Fortigate, supports AES and others. Not sure if it supports AES-GCM.

Thank you for an informative post, i'm understanding it better.

I'm not  sure what pipelining means in this context?
btanExec ConsultantCommented:
Pipelining is more of parallel processing. For this case GCM allows instruction pipelining if the hardware chip supports. See this
https://en.m.wikipedia.org/wiki/Instruction_pipelining
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