Security Basics mailing list archives
RE: Encryption question
From: "David Gillett" <gillettdavid () fhda edu>
Date: Fri, 27 Feb 2004 17:10:56 -0800
Bob checks the signature by using the public key and it is valid.
If you're saying that Bob checks it using ALICE's public key, then what this tells Bob is that the person who signed the message had Alice's PRIVATE key. i.e., It really did come from Alice. Bob should not accept a new public key for Alice without some assurance that it really did come from her. Unless the reason for the new one is that her old private key has been compromised, signing the update with her old private key could be sufficient. A message that says "here is my new public key" and is signed only with its corresponding private key is a form of social engineering attack; it's like having the name on your driver's license read "ME". Encrypting the message (NOT "signing") with Bob's public key means that only someone with Bob's private key (i.e., Bob) can decrypt and read the message. It could have been sent by anyone who had Bob's public key, which might or might not be widely known. Dave Gillett
-----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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Current thread:
- RE: Encryption question David Gillett (Mar 01)
- <Possible follow-ups>
- RE: Encryption question Marco Araujo (Mar 01)
- Re: Encryption question F.O. Bossert (Mar 02)
- Re: Encryption question Joerg Over Dexia (Mar 02)
- Re: Encryption question D.E. Chadbourne (Mar 03)
- Re: Encryption question F.O. Bossert (Mar 02)
- RE: Encryption question Daniel Menezes (Mar 02)
- RE: Encryption question Preston, Tony (Mar 02)
- Re: Encryption question Hector Luis Gimbatti (Mar 03)
- RE: Encryption question Daniel Menezes (Mar 04)