topic Re: IPsec Site to Site Tunnel Crypto in General Topics

IPsec Site to Site Tunnel Crypto

cmateam — Tue, 23 Jul 2013 17:57:27 GMT

All,

First, please forgive me if this has been asked before, I wasn't able to find anything conclusive with any good explanation.

Recently I renewed a couple of web server certificates and in doing so the CA recommended that I use SHA2 with a 256-bit message digest as SHA1 was known to have been cracked and was weak. This lead to some further digging on some of the crypto stuff for the PAN firewalls and noticed that a site-to-site IPsec tunnel I had setup nearly a year ago is using SHA1 (both are PAN firewalls). My current config is:

IKE Crypto is using:

Encryption - aes128, 3des
Authentication - sha1
DH Group - group2
Lifetime - 8 hours

IPsec Crypto is using:

ESP/AH - ESP
Encryption - aes128, 3des
Authentication - sha1
DH Group - group2
Lifetime - 1 hours

I kinda followed the 'book' based on PAN's documentation from a couple years ago, and some of the details are coming back to me, but what I am wondering if implementing some of the higher encryption/authentication standards can be done by stacking. I believe I can do this on both sides with no problem, but what I am little fuzzy on is the DH group setting and does that need to be adjusted. I found this site that explained the details a little bit more: Help - IBM z/OS Management Facility.

Additionally what has been your experience with using AES256 over AES128 for encryption - any performance issues? (IPsec crypto also supports AES128 CCM16). And for Authentication SHA512 over SHA256?

Thanks for any help.

Re: IPsec Site to Site Tunnel Crypto

tshiv — Tue, 23 Jul 2013 18:59:40 GMT

Hi,

The DH group signifies the strength of the key. Higher the DH group, stronger is the key and hence more secure. Saying that, the higher the DH group more will be the processing time as the key size is larger. Below are the numbers:

DH group 1: 768-bit key
DH group 2: 1024-bit key
DH group 5: 1536-bit key

If you you have enabled FIPS mode on the firewall and want to know what cipher suites are supported by the PA, go through the discussion on the following thread :

The key size in the AES signifies the number of repetition cycles with each cycle consisting of finite processing steps to convert a plain text into a cipher text. The repetition cycles are more in AES256 ( 14 cycles) as compared to AES128 ( 10 cycles ). The additional 4 cycles can delay the processing time.

If computing time for hash is not a concern, then SHA512 should be preferred. Note that more time to compute hash means more time to crack the hash. Hope this was helpful to you.

Regards

Tilak

Re: IPsec Site to Site Tunnel Crypto

ukhapre — Thu, 25 Jul 2013 01:40:09 GMT

Hello, there had been issues seen with DH group set for cisco devices. Can you try setting up DH as no-pfs on both ends and check?

Re: IPsec Site to Site Tunnel Crypto

cmateam — Thu, 25 Jul 2013 16:41:58 GMT

ukhapre,

In our site to site setup, we are not using and Cisco products. Both sides are PAN-2020s.