RE: Encryption question

From: Daniel Menezes (pordeus_at_email.it)
Date: 03/02/04

  • Next message: Preston, Tony: "RE: Protecting Multiple Public IP Workstations" 
    Date: Tue,  2 Mar 2004 13:24:59 +0100
To: "amon87secfx" <amon87secfx@hotmail.com>

    I think what Tony wants to say is, he can creates a key pair public/private ans publish saying that the keys belongs to Alice, but it isn't. When he encrypt a message with this private key and send to Bob, when Bob search for Alice's public key, he will find a fake key, but he won't know.

    how can we solve this? Using a trusted third party. An association that store all certificates validating one a one.

    []s

    Daniel Pordeus Menezes
    Analista de Sistemas
    Petrobras - cp37

    > Hi Tony,
    >
    > I think there's a mistake here. Digital signature is done by applying the
    > sender's private key at the message hash. The private key is known only by
    > the sender. The receiver knows that the message is not a fake one because he
    > (she) has the sender's public key to check. He (she) applies the public key
    > at the message hash to check. It's not possible to make a new private key
    > from the public key.
    >
    > Hope it helps.
    >
    > Marco Araujo
    > MCSE
    > Recife/PE - Brasil
    >
    >
    >
    >
    >
    > >From: "Preston, Tony"
    > >To: security-basics@securityfocus.com
    > >Subject: Encryption question
    > >Date: Tue, 24 Feb 2004 13:01:29 -0600
    > >
    > >
    > >
    > >Tony Preston
    > >Systems Engineer, AS&T Inc.
    > >Division of L3 Corporation
    > >(609) 485-0205 x 181
    > >
    > >I have what is a rather basic question... I probably am missing something
    > >so I thought I would ask here.
    > >
    > >Alice and Bob both have a public and private key.
    > >
    > >Alice encrypts her email to Bob using his public key. Sends the email and
    > >Bob decrypts it using his keys..
    > >
    > >Since both Bob and Alice's public keys are known, Why can't I take Alice's
    > >public key and create a key pair using any other private key. Now, I fake
    > >an electronic signature from Alice using the pair I created and send a
    > >bogus
    > >encrypted message to Bob with my "fake" Alice signature. Bob checks the
    > >signature by using the public key and it is valid. Bob assumes the
    > >message
    > >is from Alice...
    > >
    > >What prevents me from spoofing someone's electronic signature this way?
    > >
    > >
    > >
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  • Next message: Preston, Tony: "RE: Protecting Multiple Public IP Workstations"

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