Signing a key for a particular purpose - PGP

This is a discussion on Signing a key for a particular purpose - PGP ; Supose there is a george.washington@yahoo.com with whom I exchanged quite a few mails, and all his mails were signed with the key: XYZZY 1776-07-04 George Washington I never met him in person, so I can not sign his key and ...

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Thread: Signing a key for a particular purpose

  1. Signing a key for a particular purpose

    Supose there is a george.washington@yahoo.com with whom I exchanged
    quite a few mails, and all his mails were signed with the key:

    XYZZY 1776-07-04 George Washington

    I never met him in person, so I can not sign his key and certify he's
    the one true George Washington (indeed, I beleive he's not).
    Nonetheless, I would like to sign his key to tell:

    "I do not certify anything about the real identity, but I certify that
    the owner of key XYZZY is also the owner of the email address
    george.washington@yahoo.com, and he's not a spammer or one of their
    friends."

    Is there a way to do that with the current standard for PGP keys? This
    would allow to sign a lot more keys and have a thicker web of trust.

  2. Re: Signing a key for a particular purpose

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    Nicolas George wrote in
    news:c58q5f$1j4r$1@biggoron.nerim.net:

    > Supose there is a george.washington@yahoo.com with whom I exchanged
    > quite a few mails, and all his mails were signed with the key:
    >
    > XYZZY 1776-07-04 George Washington
    >
    > I never met him in person, so I can not sign his key and certify he's
    > the one true George Washington (indeed, I beleive he's not).
    > Nonetheless, I would like to sign his key to tell:
    >
    > "I do not certify anything about the real identity, but I certify that
    > the owner of key XYZZY is also the owner of the email address
    > george.washington@yahoo.com, and he's not a spammer or one of their
    > friends."
    >
    > Is there a way to do that with the current standard for PGP keys? This
    > would allow to sign a lot more keys and have a thicker web of trust.


    Signing a key does not mean that the person has his/her real name on the
    key, and it does not mean that you have personally met the person. It
    means that the key belongs to who it is suppose to belong to, and usually
    includes the idea that an included email address is correct for that
    individual. I have signed Imad's key, but have never met him or talked
    with him (except that I might have once when trying PGPfone - I'm not
    sure now). But I have had extensive online communication with him (I
    don't really know that is his real name) using his "BAD" key, and I know
    that extensive communication is with the person using that well known
    name. If I want to communicate with him, that is the key to use.

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  3. Re: Signing a key for a particular purpose

    Tom McCune wrote:

    > Signing a key does not mean that the person has his/her real name on
    > the key, and it does not mean that you have personally met the person.
    > It means that the key belongs to who it is suppose to belong to, and
    > usually includes the idea that an included email address is correct
    > for that individual.


    This depends on your personal signature policy.

    Take mine, for example: http://www.nieveler.org/PGP/pgp.htm - I would
    NEVER sign the key of a person whose identity I didn't personally
    verify, and I'll never trust somebody who signs keys from unchecked
    persons as introducer.

    If you want to sign a key for your own personal use only (so that
    mesages don't show up as invalid), at least sign it non-exportable...

    --
    Juergen Nieveler / juergen.nieveler@web.de / PGP supported!
    "Keep good relations with the Grecians."
    George W. Bush --Quoted in the Economist, June 12, 1999

  4. Re: Signing a key for a particular purpose

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    Juergen Nieveler writes:
    >Tom McCune wrote:


    >> Signing a key does not mean that the person has his/her real name on
    >> the key, and it does not mean that you have personally met the person.
    >> It means that the key belongs to who it is suppose to belong to, and
    >> usually includes the idea that an included email address is correct
    >> for that individual.


    >This depends on your personal signature policy.


    I agree that this depends on personal choices.

    >Take mine, for example: http://www.nieveler.org/PGP/pgp.htm - I would
    >NEVER sign the key of a person whose identity I didn't personally
    >verify, and I'll never trust somebody who signs keys from unchecked
    >persons as introducer.


    My most important use of PGP is for verifying signatures on opens
    source software. In most cases, I have no way to "personally verify"
    the identity of the key holder. It doesn't even matter to me what
    the person looks like. What I need to know is that this is the key
    to use to be sure that the copy of the software is not trojanized.

    [In most cases, I don't actually bother to sign -- presence of the key
    on my keyring is evidence that I have done some preliminary
    checking.]

    My point is, that often the key is important to establish a net
    identity, rather than a real-life identity. One should take the
    steps needed to be sure you are dealing with the net identity you
    intend before signing.

    For example, I don't have any questions about Tom McCune as a net
    identity, even though I have never met him. I'm guessing that he
    uses his real name, but that doesn't matter to me. So I have signed
    Tom's key, albeit with a local (non-exportable) signature.

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    -----END PGP SIGNATURE-----


  5. Re: Signing a key for a particular purpose

    Neil W Rickert wrote:

    > My most important use of PGP is for verifying signatures on opens
    > source software. In most cases, I have no way to "personally verify"
    > the identity of the key holder. It doesn't even matter to me what
    > the person looks like. What I need to know is that this is the key
    > to use to be sure that the copy of the software is not trojanized.


    But how do you know this if you can't REALLY tell that this is the real
    key of that person?

    That's why we have a web-of-trust: You don't know the guy who wrote the
    software, but you know other people. Who know other people, who in turn
    know other people who happen to know the programmer.

    > [In most cases, I don't actually bother to sign -- presence of the key
    > on my keyring is evidence that I have done some preliminary
    > checking.]


    At least you can check that all releases have been signed with the same
    key - not much, but better than nothing :-)

    > My point is, that often the key is important to establish a net
    > identity, rather than a real-life identity. One should take the
    > steps needed to be sure you are dealing with the net identity you
    > intend before signing.


    There is no difference between those indentities, IMHO

    > For example, I don't have any questions about Tom McCune as a net
    > identity, even though I have never met him. I'm guessing that he
    > uses his real name, but that doesn't matter to me. So I have signed
    > Tom's key, albeit with a local (non-exportable) signature.


    That's my point: If you use exportable signatures, you make a statement
    that you can't really make. Non-exportable signatures are just for
    convenience - Exportable keys are a matter of security and shouldn't be
    made without real checks.

    The same applies even more to signatures marking somebody as "trusted
    introducer" - doing so only for yourself (non-exportable) will only
    affect how you see other keys, but creating an exportable
    introducer-signature, you affect everybody who trusts you as an
    introducer as well (depending on what level he has set).

    I'm in favor of making LOTS of exportable signatures - without them,
    there'd be no web-of-trust. But always remember: An exportable
    signature is a public statement that YOU vouch for this key to really
    belong to that person, and that the name and address in that key are
    real. If everybody just signs keys of people for the fun of it, the
    web-of-trust would be worthless, we'd be up to our neck in fake keys
    used by scammers.

    --
    Juergen Nieveler / juergen.nieveler@web.de / PGP supported!
    I know a good tagline when I steal one.

  6. Re: Signing a key for a particular purpose

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    Juergen Nieveler wrote in
    news:Xns94C7A234D88E0juergennieveler@nieveler.org:

    >> Signing a key does not mean that the person has his/her real name on
    >> the key, and it does not mean that you have personally met the person.
    >> It means that the key belongs to who it is suppose to belong to, and
    >> usually includes the idea that an included email address is correct
    >> for that individual.

    >
    > This depends on your personal signature policy.


    Yes, PGP does allow you to make your own decision on this. And that
    decision should be made in relation to your security needs. What I said
    above is the basic concept.

    > Take mine, for example: http://www.nieveler.org/PGP/pgp.htm - I would
    > NEVER sign the key of a person whose identity I didn't personally
    > verify, and I'll never trust somebody who signs keys from unchecked
    > persons as introducer.


    Actually, I don't recall ever assigning Trust to anyone, but have thought
    about doing so for people like Phil Zimmermann and Will Price.

    > If you want to sign a key for your own personal use only (so that
    > mesages don't show up as invalid), at least sign it non-exportable...


    I think I have only ever made exportable signatures for about three
    people (I have refused requests to do so). I don't make non-exportable
    sigs for the purpose of eliminating the Invalid message, but rather to
    eliminate the possibility of anyone substituting a key on my keyring for
    a man in the middle type attack - not that it is likely that anyone would
    want to with me.

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  7. Re: Signing a key for a particular purpose

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    Juergen Nieveler writes:
    >Neil W Rickert wrote:


    >> My most important use of PGP is for verifying signatures on opens
    >> source software. In most cases, I have no way to "personally verify"
    >> the identity of the key holder. It doesn't even matter to me what
    >> the person looks like. What I need to know is that this is the key
    >> to use to be sure that the copy of the software is not trojanized.


    >But how do you know this if you can't REALLY tell that this is the real
    >key of that person?


    There are usually other ways. For example, if the MD5 sum is found
    at a usually reliable site (such as CERT), this is a pretty good
    indicator that the software is good. If the software is well known,
    from a well known site, has not been reported as trojanized, and a
    currently fetched version is identical to one that you fetched some
    time ago, that is a good indicate (though not conclusive).

    You use these sorts of checks initially, while deciding whether
    the pgp key is sufficiently trustworthy. Thereafter, the pgp
    signature should suffice.

    >That's why we have a web-of-trust: You don't know the guy who wrote the
    >software, but you know other people. Who know other people, who in turn
    >know other people who happen to know the programmer.


    Too often, this software does not connect into the web of trust, or
    only connects to signatures of unknown persons.

    >> [In most cases, I don't actually bother to sign -- presence of the key
    >> on my keyring is evidence that I have done some preliminary
    >> checking.]


    >At least you can check that all releases have been signed with the same
    >key - not much, but better than nothing :-)


    Of course.

    ----

    >I'm in favor of making LOTS of exportable signatures - without them,
    >there'd be no web-of-trust. But always remember: An exportable


    I agree with that. And I have have made those for a number of people
    that I do know well enough to make a public statement about
    (including some student at this campus). But most of those are
    people whose signatures I rarely need to check.

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  8. Re: Signing a key for a particular purpose

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    Nicolas George wrote:

    > Supose there is a george.washington@yahoo.com with whom I exchanged
    > quite a few mails, and all his mails were signed with the key:
    >
    > XYZZY 1776-07-04 George Washington
    >
    > I never met him in person, so I can not sign his key and certify he's
    > the one true George Washington (indeed, I beleive he's not).
    > Nonetheless, I would like to sign his key to tell:
    >
    > "I do not certify anything about the real identity, but I certify that
    > the owner of key XYZZY is also the owner of the email address
    > george.washington@yahoo.com, and he's not a spammer or one of their
    > friends."
    >
    > Is there a way to do that with the current standard for PGP keys? This
    > would allow to sign a lot more keys and have a thicker web of trust.


    In kgpg when signing the dialog gives me a menu to select one of: I have not
    checked at all, I have done casual checking, or I have done thorough
    checking. Is this not present in pgp? If so, the man page says to use the
    first option to sign a "persona".


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