Discussion Regarding Digital Signatures

Discussion Regarding Digital Signatures

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Discussion Regarding Digital Signatures Ari 08-01-2007
Posted by Eugene Mayevski on December 29, 2007, 12:22 pm
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Hello!
You wrote on Sat, 29 Dec 2007 10:00:27 -0500:

A> I suppose they assume that the user has been authenticated (identity)
A> which leads me to think why the signatory process couldn't be tied to
A> the verification process. hmmm....

I am not sure that I understand your point/question. The problem with
absense of timestamping is that when the signature is verified several years
later, the certificate, used to sign the document, will most likely be
expired. If there's no timestamp, the validator will alert the user that the
certificate has expired. If the certificate is revoked and this is
discovered by the validator, the validator will complain about this too.

Timestamping lets the validator check when the timestamp was made and not to
alert the user about the expired certificate. If the certificate was
revoked, the validator will compare the revocation moment with the timestamp
and will have a chance to figure out whether the signature was made with a
valid or revoked certificate.

Timestamping authority timestamps the signature (to be precise, the hash of
some data), it doesn't care about what was used to produce the hash.

With best regards,
Eugene Mayevski


Posted by Ari on December 31, 2007, 4:22 am
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On Sat, 29 Dec 2007 19:22:00 +0200, Eugene Mayevski wrote:

> Hello!
> You wrote on Sat, 29 Dec 2007 10:00:27 -0500:
>
> A> I suppose they assume that the user has been authenticated (identity)
> A> which leads me to think why the signatory process couldn't be tied to
> A> the verification process. hmmm....
>
> I am not sure that I understand your point/question. The problem with
> absense of timestamping is that when the signature is verified several years
> later, the certificate, used to sign the document, will most likely be
> expired. If there's no timestamp, the validator will alert the user that the
> certificate has expired. If the certificate is revoked and this is
> discovered by the validator, the validator will complain about this too.
>
> Timestamping lets the validator check when the timestamp was made and not to
> alert the user about the expired certificate. If the certificate was
> revoked, the validator will compare the revocation moment with the timestamp
> and will have a chance to figure out whether the signature was made with a
> valid or revoked certificate.
>
> Timestamping authority timestamps the signature (to be precise, the hash of
> some data), it doesn't care about what was used to produce the hash.

I see what your saying but the most important process is the authentication
of the *identity* of the signer. If there is no ID that is verified, then
the rest doesn't matter. I can use your Adobe on your computer to sign in
your name as long as I can get to your software.

Which is my point. Why not incorporate the system that determines that it
is *you* accessing your Adobe, or PDFBlackBox seamlessly with the digital
signature capabilities? Rather than have two or more programs to do this.

Posted by Eugene Mayevski on December 31, 2007, 4:51 am
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Hello!
You wrote on Mon, 31 Dec 2007 04:22:28 -0500:

A> I see what your saying but the most important process is the
A> authentication of the *identity* of the signer. If there is no ID that
A> is verified, then the rest doesn't matter. I can use your Adobe on your
A> computer to sign in your name as long as I can get to your software.

That's a totally different story. Digital signatures don't prove the
identity of the user, they prove the set of "what the person has" and "what
the person knows". With digital means you can't reliably prove "what the
person is", i.e. whether the signature or fingerprint - once they are placed
into the document, they can be duplicated.

Example: you can copy the signature (or fingerprint) from the document I
signed, then come to my computer and use it to create another document.
Afaik there's no reliable solution for this problem.

With best regards,
Eugene Mayevski


Posted by Ari on December 31, 2007, 5:41 am
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On Mon, 31 Dec 2007 11:51:20 +0200, Eugene Mayevski wrote:

> Hello!
> You wrote on Mon, 31 Dec 2007 04:22:28 -0500:
>
> A> I see what your saying but the most important process is the
> A> authentication of the *identity* of the signer. If there is no ID that
> A> is verified, then the rest doesn't matter. I can use your Adobe on your
> A> computer to sign in your name as long as I can get to your software.
>
> That's a totally different story. Digital signatures don't prove the
> identity of the user, they prove the set of "what the person has" and "what
> the person knows". With digital means you can't reliably prove "what the
> person is", i.e. whether the signature or fingerprint - once they are placed
> into the document, they can be duplicated.
>
> Example: you can copy the signature (or fingerprint) from the document I
> signed, then come to my computer and use it to create another document.
> Afaik there's no reliable solution for this problem.
>
> With best regards,
> Eugene Mayevski

Yes, that is what I am saying, why not have a single program that will do
both? Your identity is carried to the signature; if the signature is
queried, the ID proof could emerge as well.

Posted by Arthur T. on December 31, 2007, 2:23 pm
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>Hello!
>You wrote on Mon, 31 Dec 2007 04:22:28 -0500:
>
> A> I see what your saying but the most important process is the
> A> authentication of the *identity* of the signer. If there is no ID that
> A> is verified, then the rest doesn't matter. I can use your Adobe on your
> A> computer to sign in your name as long as I can get to your software.
>
>That's a totally different story. Digital signatures don't prove the
>identity of the user, they prove the set of "what the person has" and "what
>the person knows". With digital means you can't reliably prove "what the
>person is", i.e. whether the signature or fingerprint - once they are placed
>into the document, they can be duplicated.
>
>Example: you can copy the signature (or fingerprint) from the document I
>signed, then come to my computer and use it to create another document.
>Afaik there's no reliable solution for this problem.

-----BEGIN PGP SIGNED MESSAGE-----

You're forgetting that a good digital signature is a
transformation of a secure hash of the original. Take this
signature and see if it works with any other document:

-----BEGIN PGP SIGNATURE-----
Version: PGPfreeware 6.5.3 for non-commercial use
<http://www.pgp.com>

iQCVAwUBR3k7HkktjQmm3DQRAQFsLgP+ILXyjljJPm3A3xWt1XF6xoS4sK9W0t8e
rYjnAG5M04CJtL3yqNgLj3S+ntOAMHauzvDfTKX3ZEWAjNc1zzXI+jt2y7GtpYsu
vevdhu7Fw+kMQw07l1VqamNgeQTda2HCZMg5qDGzJltEvVOj70373sYGrOWKKWB4
PFhyX4vxEQQ=
=88A3
-----END PGP SIGNATURE-----


--
Arthur T. - ar23hur "at" intergate "dot" com
Looking for a z/OS (IBM mainframe) systems programmer position

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