Disable the unsupported hashing algorithm SHA256 message

Problem details

When digitally signing a PDF in Adobe Acrobat or Acrobat Reader, the following message appears:
Your signature device does not support the required hashing algorithm SHA256. Do you want to continue using the deprecated SHA1 algorithm or cancel the signature?  

Your signature device does not support the required hashing algorithm SHA256 message

You get the above message even after trying the following settings:

aSignFormat=adbe.pkcs7.detached
aSignHash=SHA

Environment

  • Adobe Acrobat, Acrobat Reader
  • Windows

Steps

  1. Quit the Acrobat or Acrobat Reader application if it's already running.

  2. Open the registry editor -  go to Run (Windows menu + R), type regedit.exe in the Open field, and select OK.

  3. In the registry editor, based on your installed version of the product, go to the version-specific location listed below

    For Acrobat (Continuous):

    • Location: HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\DC\AVAlert\cCheckbox

    For Acrobat (Classic - Acrobat 2020):

    • Location: HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\2020\AVAlert\cCheckbox

    For Acrobat (Classic - Acrobat 2017):

    • Location: HKEY_CURRENT_USER\SOFTWARE\Adobe\Adobe Acrobat\2017\AVAlert\cCheckbox
  4. Create a key of type DWORD and name it iDontShowSHA1Dep. Change its value to 1 (one).

    Note:

    When the value of iDontShowSHA1Dep is:

    • 0: The security warning dialog is enabled in Acrobat
    • 1: The security warning dialog is disabled in Acrobat
  5. Close the registry editor.

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