implications of subkeys?

[Len Sassaman]

So, the idea behind signing subkeys is pretty cool, but the drawback is it
takes an already overly complicated system and makes it that much more
complicated. (This is why, I believe, PGP doesn't support it. Although I
do wish that PGP understood such keys...)

The basic idea is that you can collect your trust (signatures from other
people) on the master signing key, which binds the subkeys to itself.
Then, when you retire old keys and generate new ones (you do do this on a
regular basis, right?) you don't have to worry about regaining trust,
since trust isn't calculated on subkeys.

This isn't actually needed, however, due to a trick in the PGP trust
model that isn't too widely known:

If a key A bearing a given user-id signs a key B with an identicial
user-id (and the signature is made on that identical user id) then trust
for key B is calculated as though all the signatures for this shared
user-id on key A were made on key B. This was introduced around the time
of PGP 3.0, to prevent an RSA/DSA divide in the web of trust.



On Wed, 27 Feb 2002, Nick Andriash wrote:

> Hello Alex,
>
> On Wednesday, February 27 2002 at 05:25 AM PDT, you wrote:
>
> > Others can't sign a subkey (or a primary key)- they sign  the UIDs which are
> > atatched to a primary key.
>
> Alex, Frank and Dizss... That sounds simple enough, and thank you. I
> think another aspect which is confusing to me is the term "Master
> Signing Key", and then "signing subkey", which is, as I understand it,
> something PGP doesn't offer. So, in an attempt to understand this,
> myself and other people sign my UID(s), while my (owner) signature is
> also attached to any subkey, be it signing or encryption, correct?
>
> What is the purpose behind a signing subkey, and how does it differ from
> the Master (Private) Key which I presume is also used for signing... or
> are they one in the same? Can one change a signing subkey without it
> affecting the Master Key? Can others still verify your signature even if
> you change your signing subkey without having to issue a new Public Key?
>
>
> --
> Nick Andriash
> Courtenay, B.C. Canada
>
>
>
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--Len.