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Access to EFS encrypted files using same domain login across network, or not?

Posted on 2004-09-02
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Last Modified: 2013-12-04
I'm surprised to find that when I'm logged in with my domain account I can't seem to access EFS encrypted files on a shared directory on another (domain member) machine (the files were encrypted using the same account login, and I was logged into the machine that they are stored on).  I can browse the directories, but can't open the files.

Is this a feature, or have I managed to stuff something, or is there a "setting" required? I just don't seem to be able to find any information about this.

Seems a bit odd if you can't do this.

Thanks

Dave Turnbull
PS: I really don't understand how to assign "points" to this question. Obviously it is "easy" if you know the answer?
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Question by:DaveTurnbull
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5 Comments
 
LVL 3

Expert Comment

by:Gargantubrain
ID: 11968791
I tested this and it works in my Windows 2000 domain. I encrypted a file from my XP workstation in a directory on the domain controller. I went and opened the file on another workstation after logging on as myself.

Is the shared folder on the domain controller? Unless you export the key (not recommended, the keys are supposed to stay on the more secure domain controllers) this will probably only work with folders shared on your domain controllers.
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Author Comment

by:DaveTurnbull
ID: 11970871
Hi
Thanks for trying it out.

Up to now the domain controller was not involved/tested, just workstations (all domain members). I have now repeated some tests:

1) Like from other WS(s), from the domain controller I can not access the encrypted files on the WS on which they were encrypted (same domain account login).
2) If I login into the domain controller and encrypt a file on it I CAN access the file from a WS.
3) If I login to a WS and encrypt a file on the domain controller I can then access it from the domain controller (the encryption process seems to take longer though (with a miniscule test file))

So, cross-machine access to encrypted files works, but only if the encrypted files are on the domain controller.

So, I guess the question still is, can I / how do I get WS to WS access to encrypted files?
[These are two "development" machines with local file stores, I want to protect the information on them in case the machines are compromised.]

This "export the keys" lark. Where do I read about it?

Thanks again

Dave Turnbull
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LVL 6

Expert Comment

by:Scott_Willcocks
ID: 11973216
the reason that you can't use it for WS to Ws is that the workstations do not share a common certificte on the machines what you will need to do is export the client certificate from each PC

heres how then

http://www.compulink.co.uk/~davedorn/computing/windows/xpencrypt3.htm



install the exported certificates on each others machines

the certificates that you export from pc1 need to go on pc2 the certificte exported from pc2 need to go on pc1 but remeber to back these up and install ino your certificate server just in case or stor somewhere safe if any of these certificates go missing you will not be able to recover the files easily.

where the certificate store is

in IE browser go to tools > internet options > content > certificates

the rest of the instructions are in the link
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Accepted Solution

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Scott_Willcocks earned 50 total points
ID: 11973256
both workstations need each others certificates so they can encrypt and decrypt  the files if one person encrypts unless they have the other machines certificate then they can't decrypt it and vice versa. the reason that you can on the server is that as part of the domain they have a recovery key certificate that you can use to decrypt the files on the server but on domain admin can if they encryptr using the local certificates you may not be able to decrypt if anything goes wrong with one of the machines so make sure you have a backup of the certificate we cannot express how important it is.
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Expert Comment

by:Gargantubrain
ID: 11973361
As I mentioned before, exporting your key is a security risk. It opens the possibility of someone gaining access to your key, and therefore ALL your encrypted files.

Please be aware of the risks before you import your key into any machine that is out of your control.

The procedure mentioned to export your key is for the purpose of backing it up in case you need to re-install your operating system on a standalone machine. Without a backup of your key, the encrypted files are no longer accessible after an OS re-install because the user accounts (and therefore the keys) are re-created.

EFS is not a perfect solution for file encryption, and you should be aware of what it can and cannot do before you depend on it. There are other methods to encrypt files that may better suit your requirements. The biggest advantage EFS has is transparent encryption -- the files can be opened by an application without first decrypting them. If that is something you can live without, then perhaps an alternative method of encryption would work better for you.
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