Magento implements the Authorize.Net Direct Post payment method, using Authorize.Net’s AIM (Advanced Integration Method) and DPM (Direct Post method) APIs, which use MD5 based hash.
Authorize.net will stop supporting MD5 based hash usage on March 14, 2019
Starting from this date, Magento Open Source, Magento Commerce and Magento Cloud merchants will not be able to process payments using Authorize.Net Direct Post payment method. To be able to continue successfully process payments using these methods, merchants need to apply the patch provided by Magento and replace the existing MD5 hash with a Signature Key in the Magento Admin configuration settings.
Further are described the three general steps you need to take be able to continue using Authorize.Net Direct Post payment method.1. Download and APPLY THE PATCHYou may require developer assistance to apply the update. To update, you can download and install packages for your Magento edition and version. Download patches also available for those who installed with Composer.
2. GET A NEW SIGNATURE KEYYou need to get a new Signature Key and add it to your Magento Admin configuration. For more information, see What is a Signature Key?
3. UPDATE MAGENTO ADMIN CONFIGURATIONSetup new signature key in Magento admin
Need help to install this patch in your website. Please contact usHave questions, please chat with us in Skype: mage.support