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  1. #1
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    WinXP EFS: is it compatible with Win7 EFS and Win10 EFS?

    Hi all,
    I have a WinXP machine that is able to process its own EFS files just fine.
    My Win7 and Win10 boxes can also open files created on it, and they can open files created on each other.
    But the WinXP box doesn't seem to want to open EFS files created on the Win7 or Win10 box.
    Of course, I can't find any information in the documentation on backwards compatibility.
    Does anyone here have an example where they can open a Win7 or Win10 EFS file on their WinXP box?
    Is there something special that needs to be done on the XP box to make things fully interchangeable?
    Thanks in advance.
    Dave

  2. #2
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    The first time an acronym or initials show in a sentence or paragraph the actual name should be used, just too many possibilities of they stand for, especially for those who have not seen them before. In the case of EFS the gamut includes food and finance but since this is a computer forum it probably means Encryption File System (Intel).
    https://www.acronymfinder.com/EFS.html
    https://duckduckgo.com/?q=Encryption...2-3_j&ia=about
    I'm going out on a limb with the thought that it may involve whether the version of Windows involved is 32-bit or 64-bit. WinXP Pro was the first to be available as either 32-bit/x86 or as 64-bit/x64. Then there was the IA-64/Itanium mostly used as servers.
    https://duckduckgo.com/?q=itanium&t=...2-3_j&ia=about

  3. #3
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    Hi Burton,
    Interesting thought: 32 vs 64 bit, as indeed the machines in question are on either side of that divide. The encryption used ought to be independent of CPU word length, but that's exactly the kind of thing that would cause bugs. Particularly in a MSFT backwater like EFS. And of course, this would be totally undocumented. Thanks for the idea...gives me something to investigate further.
    FWIW, the keys pretend to import just fine into their respective stores. The EFS cipher command in XP is way primitive, so you can't really see what's going on the way you can in Win7/10.
    Silly side-light: I deliberately don't spell out acronyms in technical forums. Why? Because I want the person answering to know at least as much as I do. Too often, forum replies are full of misinformation that ends up wasting a lot of readers' time...people trying to be helpful, but adding far more noise than signal.
    David

  4. #4
    5 Star Lounger tonyl's Avatar
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    I believe Windows XP SP1 onwards uses the same algorithm as Windows 7. I'm not sure about Windows 10, which probably uses an updated one, but I would've thought it was backwards-compatible.
    Last edited by tonyl; 2019-02-06 at 08:59. Reason: changed "different" to "updated"

  5. #5
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    Just to add to the weirdness, some data:
    - I now have the XP machines using exactly the same key as the Win7 and Win10 machines (obviously, all are Pro edition)
    - All machines have DRA rights on the others
    - All machines can decrypt files created on XP
    - XP machines cannot decrypt anything from Win7 or Win10
    - Win7 and Win10 are fully interoperable
    - All keys (certificates, really) are the same version (V3, 2048 bits)

    When I look at a file's properties created by Win7, but reading on XP...the "details" area of the "advanced" properties sheet points to the correct key and the correct DRAs.

  6. #6
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    Hi all,
    Well, I just spun up yet another WinXP Pro 32 bit computer, and on THAT one, the EFS files open up just fine.
    So, there's something fishy with the first two WinXP boxes I was working with...dunno, will investigate in my copious free time.
    But I've proven that Win10-Win7-WinXP are fully compatible for EFS files.

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    RockE (2019-02-11)

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