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Re: [Openvpn-users] secret key question


  • Subject: Re: [Openvpn-users] secret key question
  • From: "James Yonan" <jim@xxxxxxxxx>
  • Date: Fri, 9 Apr 2004 06:21:39 -0000

Sara,

It's a good question -- not all of the bits in the --secret key file are
actually used for key material.  Different ciphers and HMAC hashes need a
varying amount of entropy for key material, and the 2048 bit OpenVPN static
key file format is designed to have enough entropy to seed large-key ciphers
such as AES-256.

Basically the 2048 bits of entropy are divided 4 ways:

encrypt cipher (512 bits)
encrypt HMAC   (512 bits)
decrypt cipher (512 bits)
decrypt HMAC   (512 bits)

This is considerably future-proofed, as most ciphers in common use today use
128 bit keys, and the SHA1 hash uses 160 bits of key material.

So if you tweak a bit in the key file that isn't used, it won't have any
functional effect.

James 

sara <srps1579@xxxxxxxxxxx> said:

> I am using a key based authentaication for my vpn set
> up.
> I created a seceret key in the server and copy that
> key to my client side and everyhing works
> fine.Yesterday i opened that secret key in editor and
> deleted 2 or 3 lines in the key file.After this i
> start the the vpn and it is creating the peer
> connection.What is going wrong here?.I think the VPN
> connection sud be established only if the secret keys
> are matching both the sides.I just followed the steps
> in the howto in openvpn website.So there is nothing
> wrong in my configuration.
>                                            --Sara
> 
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