Oracle says that starting with April 18, 2017, Java (JRE) will treat all JAR files signed with the MD5 algorithm as unsigned , meaning they'll be considered insecure and blocked from running. Oracle originally planned MD5's deprecation for the current Critical Patch Update, released this week, which included a whopping 270 security fixes , one of the biggest security updates to date. The company decided to give developers and companies more time to prepare and delayed MD5's deprecation for the release of Oracle Java SE 8u131 and the next Java CPU, scheduled for release in April...
Oracle removed MD5 as a default code signing option from Java SE 6, released in 2006. Despite this, there will be thousands of Java apps that will never be resigned. For this, Oracle will allow system administrators to set up custom deployment rule sets and exception site lists to allow Java applets and Java Web Start applications signed with MD5 to run. Sometimes in the second half of 2017, Oracle also plans to change the minimum key length for Diffie-Hellman algorithms to 1024 bits. These updates are part of Oracle's long-standing plan for changes to the security algorithms in the Oracle Java Runtime Environment and Java SE Development Kit.