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Re: key processing for manual and dynamic SA
> 1) Manual Mode SA.
>
> As an example, I need to prompt the UI for a DES session key for an ESP SA.
> DES only actually requires a 56bit stream to do the calculation - although
> this 56bits is expanded to include parity-bits (probably for historic
> reasons - pre parity memory?).
>
> Should the UI ask for 56bits (14 hexadecimal digits) and then expand with
> parity bits and check against the weak-key list, or should the UI ask for
> 64bits.
I ask for 64 bits, and AFAIK everyone else's does too.
> The problems with asking for 64bits are :
>
> a) either the use is expected to get the parity bit right
> b) or the management code applies the parity automatically
>
> a) is too much to ask and b) changes the key.
I do b), because it only changes the key if the parity is wrong.
> For the sake of interop, I think we need to decide on a common way of
> presenting keying material at the UI. If one end of the link takes 56bits,
> and the other takes 64bits, converting between the two over the 'phone
> is not straightforward!
Everytime I've seen manual keys thrown around, it's been in 64-bit
quantities. That's what we've done at the interoperability events.
> It sounds easiest (to me), if we could agree on using the non-parity
> version of the required key, where parity is an issue. Then I can easier
> 'communicate' manual keys without worrying about parity.
If the implementation fixes parity, you don't have to worry about it. If you
and your friend agree that 1234567890abcdef is a good key, who cares if it
gets adjusted to 1334577991abcdef (the standard "low-bit-parity" method)?
> 2) Dynamic Mode SA
You're right in that the derivation better be the same on both systems.
> Question: What do I do if the constructed 64bit key is weak? Do I:
> a) reject the establishment
We discussed this before I think, and IIRC, the conclusion was to reject the
establishment if weak key checks fail.
Dan
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