Re: Encryption Key Question

From: David Heise (dheise_at_gmail.com)
Date: 03/03/05

  • Next message: L. Walker: "Re: anyone who saw this arp traffic?" 
    Date: Thu, 3 Mar 2005 14:04:59 -0700
To: Simon Zuckerbraun <szucker@sst-pr-1.com>

    Essentially its not about the user, its about the software. I want to
    ensure that only my software can talk to my webservice and vice versa.
    I don't care about the user, or who is using it, but the application.
    So, the thought is to have a unique method of sending and recieving
    data...namely encryption. The user will supply credentials and
    authenticate on top of this extra layer.

    On Thu, 03 Mar 2005 14:10:06 -0600, Simon Zuckerbraun
    <szucker@sst-pr-1.com> wrote:
    > David: If I'm understanding you correctly, you have the following
    > situation: An application, running on behalf of a particular user, has a
    > piece of sensitive data that must be stored on the local computer. You
    > are looking for a way to encrypt that data before storing it, so only
    > that user will be able to access the data. Any other individual who gets
    > access to the machine will not be able to access the data.
    >
    > Some operating systems have a facility for performing exactly that task.
    > In Windows, this is known as DPAPI.
    >
    > Zaven: Here's a very quick explanation of how DPAPI works in Windows.
    > For each user in the system, Windows generates a random "master key"
    > used to encrypt the user's secrets. The master key is stored as part of
    > the user's profile, encrypted with a key that is derived from the user's
    > password. Unless the user is logged on to the system with the proper
    > password, the master key can not be decrypted. (Warning! This is a bit
    > oversimplified, as I am about to explain...)
    >
    > Enormous complications result from the fact that we need to be able to
    > deal with password changes and resets. If the user forgets his password
    > and an administrator forcibly resets it to a different string, there has
    > to be some way for the user to regain access to his master key (which
    > sits encrypted using the original password). Microsoft went to great
    > lengths to ensure a proper balance between security and reliable means
    > of recovery in the case of such interruptions in normal operations. In
    > practice, the effectiveness of DPAPI depends on certain details of how
    > the machine is configured; high-security configurations are achievable.
    >
    > I could go on and on about this. It's a topic that never ceases to
    > facinate me.
    >
    > Lots can go wrong. Apply Keychain Manager was found to have a bad
    > security hole (http://seclists.org/lists/bugtraq/2004/Jul/0166.html). I
    > don't know the current status of that issue.
    >
    > David: You will find out - either that, or you've already found out -
    > that there are no universal solutions in security. Every proposed
    > solution has to be carefully evaluated to ensure that it accurately
    > addresses the threats that are relevant. So I need to add this word of
    > caution: I'm not telling you for sure that DPAPI (or the equivalent on
    > another OS) is necessarily the appropriate solution to the problem you
    > are working on. That's something that can only be decided after a
    > careful, holistic study of the environment in which your system will
    > operate, and the potential threats that need to be defended against.
    >
    > Simon
    >
    > > -----Original Message-----
    > > From: Zaven [mailto:zaven@sonic.net]
    > > Sent: Wednesday, March 02, 2005 11:21 PM
    > > To: David Heise; security-basics@securityfocus.com
    > > Subject: Re: Encryption Key Question
    > >
    > >
    > > David Heise wrote:
    > >
    > >> Here's my question:
    > >> What is the best method of storing this passphrase internally in the
    > >> application such that it would be as secure as possible?
    > >
    > > AFAIK, you can't store the passphrase anywhere securely. You should
    > > think in terms of requiring the user/other process/whatever to input the
    > > passphrase in to authenticate, and then storing only the hash digest.
    > >
    > > If anyone knows how (e.g., Apple Keychain Manager) manages to diaplat
    > > the plaintext of stored passwords, I'd like to know, because it makes me
    > > nervous :)
    > >
    > > Zaven
    > 

    -- 
David B Heise [dheise@gmail.com]
http://endofuniverse.blogspot.com      Personal Blog
http://students.cs.byu.edu/~dheise    Personal Web
http://www.stonetempest.com           Company
  • Next message: L. Walker: "Re: anyone who saw this arp traffic?"

    Relevant Pages

    • RE: Encryption Key Question
      ... Here's a very quick explanation of how DPAPI works in Windows. ... For each user in the system, Windows generates a random "master key" ... used to encrypt the user's secrets. ... David: You will find out - either that, or you've already found out - ...
      (Security-Basics)
    • Re: CryptAcquireContext returns NTE_BAD_KEY_STATE?
      ... The Microsoft software CSPs encrypt the private keys using DPAPI ... which encrypts this using a master key. ...
      (microsoft.public.platformsdk.security)
    • Re: Back Doors
      ... >> Design into the system a master key. ... Encrypt that with public key. ... Decrypt random symmetric key with private key. ...
      (sci.crypt)
    • Security log Error 596
      ... when I go to request a certificate I ... > Backup of data protection master key. ... DPAPI is used to encrypt secrets (like EFS encryption ... domain recovery key. ...
      (microsoft.public.windowsxp.security_admin)
    • Re: secrets of the EFS key pair maker
      ... DPAPI doesn't use the password when it generates ... encrypt master key with key-from-password; ... generate symmetric FEK ...
      (microsoft.public.windowsxp.security_admin)