I believe what the NetScreens do is, by this definition, pre-shared keying. The extra wrinkle here is that NetScreen allows you to enter the key in hexadecimal, or enter a "password" from which it will generate the necessary key. (It is easier to transmit such a password over the phone, or memorize it, than to try to duplicate the hexadecimal value at a remote location.
The password->key generation feature will generate different sizes of key, depending on the encryption method selected. The poster is finding that it is generating only 2/3 the key length that he expects for the selected encryption, 3DES-CBC. I don't have a NetScreen manual handy, but I suspect that this is one of the 3DES flavours that re-uses one of the keys, so although there are three steps, only two keys are used. (Giving an effective strength of 112 bits instead of 168). I've held off answering, in hopes that someone with a manual or other hard information would speak up.... Dave Gillett On 11 Jan 2002, at 17:47, Ben Nagy wrote: > Are you sure you want to use manual keying? Especially with 3DES, which > is one of the most secure IPSec choices if used correctly? > > I may be falling victim to some Netscreen terminology blunder, but > "Manual Keying" normally means that the actual keys used by the ESP and > AH encryption algorithms (3DES in your case) are fixed manually at each > end. This is bad, since there will be no re-keying, ever, and you'd need > to have a way of transferring the keys to each site so that they can be > typed in and then arrange for some sort of key-change schedule, > otherwise you'll end up sending all your data under one key. This is > both fragile and possibly insecure, depending on how much of the > differential analysis stuff you buy into for DES. > > Note that manual keying isn't the same as "pre-shared keys" which are > used to generate keys that are used in IKE (Internet Key Exchange > protocol), which then takes care of all the keying, re-keying and > associated issues for both ESP and AH, in a secure manner. In a good > IPSec setup the keys are changed (by IKE) regularly, and the negotiation > phase of IKE would use either digital signatures or one of the public > key modes. My _personal_ favourite is probably using "RSA encrypted > nonces" with large (1024+) keys, or digital sigs with a self-maintained > CA. > > The long and the short of it is that manual keying is really only for > testing purposes or for EXTREMELY hardcore crypto freaks who have a > super secure out-of-band key exchange protocol, with associated rotation > and re-keying regimes. > > If you know all this, and you're actually implying that you mistrust IKE > for some reason, please let me know, because I'd be very interested in > any discussion suggested that it is flawed. If none of this made any > sense, then let me know and I'll be less terse! > > Cheers, > > -- > Ben Nagy > Network Security Specialist > Mb: +61 414 411 520 PGP Key ID: 0x1A86E304 > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED]] On Behalf Of Warren van Eyssen > > Sent: Friday, January 11, 2002 5:17 PM > > To: Firewalls (E-mail) (E-mail) > > Subject: Netscreen 5xp 3Des Keys > > > > > > Hi All, > > > > Can anybody help with the following problem > > I have a Netscreen 5xp OS Ver 3.0.0r1.0 > > I want to use 3Des-CBC Manual Key encryption[...] _______________________________________________ Firewalls mailing list [EMAIL PROTECTED] http://lists.gnac.net/mailman/listinfo/firewalls
