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Thread: Unsure about the iso-verification (gpg-verification)

  1. #1
    Join Date
    May 2021
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    Unsure about the iso-verification (gpg-verification)

    Hello community,

    I'm really looking forward to try (K)ubuntu but I've got a problem with understanding the verification of the iso...

    In general I understand what I have to do:

    1) download iso, sha256 and gpg-file
    2) then verify the sha256-checksum-file with help of the gpg file
    3) then verify the iso file with the sha256-checksum-file

    I'm using these instructions: https://ubuntu.com/tutorials/how-to-...ha256-checksum

    After adding the server-keys to my "keyring" (step 4), I type "gpg --keyid-format long --verify SHA256SUMS.gpg SHA256SUMS.txt" in the console to verify the checksumfile. My output is something like this:

    "gpg: Signature made 01.04.2021 18:12:56 Mitteleuropäische Sommerzeit using RSA key ID D94AA3F0EFE21092
    gpg: Good signature from "Ubuntu CD Image Automatic Signing Key (2012) <cdimage@ubuntu.com>" [unknown]
    gpg: WARNING: This key is not certified with a trusted signature!
    gpg: There is no indication that the signature belongs to the owner.
    Primary key fingerprint: 8439 38DF 228D 22F7 B374 2BC0 D94A A3F0 EFE2 1092"

    This seems good to me... But: I only get the verification for this one "RSA Key ID D94...." In the Description theres another second "DSA key ID 46..." in the output-message. Another description I found also says that I have to check the two "Good Signature from..." Messages.
    Why don't I get the OK for both keys? Is my file okay? I added both keys to my "keyring" like in the description before... Why are there two btw?

    Btw I tried it with Ubuntu and Kubuntu 20.04.2 LTS.

    Thanks a lot for your support and excuse my english. Its not my home-language.

    Cheers

    Thanks a lot
    Last edited by fj7hUtJ83S@; May 7th, 2021 at 07:50 AM.

  2. #2
    Join Date
    Oct 2004
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    Ubuntu Budgie

    Re: Unsure about the iso-verification (gpg-verification)

    It just means the mostly deprecated DSA key was not used for verification.
    DSA keys were provided on Trusty but [soon] afterwards no longer used.

    The tutorial you reference does correctly state (my emphasis):
    "...tells us which key or keys were used to generate the signature file."

    So in this case it is the RSA key.
    /path/to/Truth

  3. #3
    Join Date
    May 2021
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    2

    Re: Unsure about the iso-verification (gpg-verification)

    Great. Thank you!

    So this one key is sufficient, and tells me, that the checksum file is correct and original, right?

    And just to make sure, that I understood the last step correctly: In the last step (6) I compare the checksum in the checksum-file with the checksum of the iso. The command "sha256sum -c SHA256SUMS 2>&1 | grep OK" doesn't work. Probably because the program sha256sum is missing. Is it also a possible way to use the command "get-filehash ubuntu......iso" in windows powershell? My output then is a sha256 checksum.
    When my output checksum then matches with the checksum in the checksum-file, it's safe!?


    Thanks again. After this info the topic is solved.

  4. #4
    Join Date
    Jun 2007
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    Arizona U.S.A.
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    5,002

    Re: Unsure about the iso-verification (gpg-verification)

    There is also a little utility named GtkHash that does all the work.
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