Re: Encryption question

From: Hollis Johnson (hollis_at_cisco.com)
Date: 02/26/04

  • Next message: Gideon T. Rasmussen, CISSP, CISM, CFSO, SCSA: "Re: How to find a changing IP on ethernet network" 
    Date: Wed, 25 Feb 2004 16:36:11 -0800
To: Lars Georg Paulsen <maillist@braindead.nu>, "Preston, Tony" <Tony.Preston@acs-inc.com>, security-basics@securityfocus.com

    Lars. That's interesting. I always thought Priv/Pub keys had to be composed
    of two primes. If you "combine" them (i'm thinking p*q) the result is no
    longer prime -- although it may not be any easier to break -- Is that what
    you meant? or did you mean applying one then the other??

    Thanks for any additional info :-)

    Hollis

    At 07:17 PM 2/25/2004 +0100, Lars Georg Paulsen wrote:
    >The encrypted key you have made, is not valid. Bob can't decrypt the
    >messange with his public nor with is private.
    >
    >If alice sends a message to bob, and what him to be the only one to read
    >it, she will encrypt it with his public key. And to make sure bob can
    >trust the message, and tell for sure it's from alice, she will sign the
    >message with alice private key.
    >
    >What you think of, combinding a private key and a public to make a new
    >key, is the himlich method. The way describe above takes quite long time
    >to decrypt.
    >
    >Another scenarior, is to make to new keys that are identical.
    >This you do by combinding private keys and public keys.
    >Alice makes a new key with her private and bobs public key.
    >Bobs makes a new key with his private and alices public key.
    >The two new keys are now identical, can not be produced by any
    >outsiders.
    >
    >Hopes this answer a bit of your question.
    >
    >regards
    >Lars Georg Paulsen.
    >
    >On Tue, 2004-02-24 at 20:01, Preston, Tony wrote:
    > > 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?
    > >
    > >
    > >
    > > ---------------------------------------------------------------------------
    > >
    > ----------------------------------------------------------------------------
    > >
    > >
    > >
    >
    >
    >---------------------------------------------------------------------------
    >----------------------------------------------------------------------------

    ---------------------------------------------------------------------------
    ----------------------------------------------------------------------------

  • Next message: Gideon T. Rasmussen, CISSP, CISM, CFSO, SCSA: "Re: How to find a changing IP on ethernet network"

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