I am using Magento2.3 and download the Authorize.net Direct Post Signature Key Patch file and put it to magento's root directory then go to the putty and run below command:
It is not working for me.
Now Apply Patch directly in vendor folder
This patch is applicable on all Magento 2.x and 1.x versions.
Alternatively you can use patched files from following address and replace them in your vendor folder.
If Need Run
php bin/magento setup:upgrade; php bin/magento setup:static-content:deploy -f;