RE: Encryption question

From: Gene LeDuc (Gene.LeDuc_at_tns-md.com)
Date: 02/25/04

  • Next message: Lars Georg Paulsen: "Re: Encryption question"
    To: "'Preston, Tony'" <Tony.Preston@acs-inc.com>
    Date: Wed, 25 Feb 2004 12:45:12 -0500
    
    

    Alice encrypts the message to Bob using Bob's public key and then signs it
    using her private key. Bob verifies that the message is from Alice by using
    her public key to check the signature and then decrypts the message with his
    private key. The encryption only hides the contents, it does not
    authenticate the message. The signing authenticates the message but does
    not hide the contents. You need both if you want to have a secure
    conversation.

    -----Original Message-----
    From: Preston, Tony [mailto:Tony.Preston@acs-inc.com]
    Sent: Tuesday, February 24, 2004 11:01 AM
    To: security-basics@securityfocus.com
    Subject: Encryption question

    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: Lars Georg Paulsen: "Re: Encryption question"

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