Fix crash with recent Java 8 versions for old forge modpacks

This applies to old Forge modpacks that crashed on startup with the new versions of Java.
The crash may look as follows:

2024-02-28 10:35:15 [SEVERE] [Forestry] myrathi.flatsigns.FlatSigns failed validation. Halting runtime for security reasons. Please replace your mods with untampered versions from the official download sites.
2024-02-28 10:31:56 [SEVERE] [ForgeModLoader] The minecraft jar file:/home/********/.var/app/org.prismlauncher.PrismLauncher/data/PrismLauncher/libraries/com/mojang/minecraft/1.6.4/minecraft-1.6.4-client.jar!/net/minecraft/client/ClientBrandRetriever.class appears to be corrupt! There has been CRITICAL TAMPERING WITH MINECRAFT, it is highly unlikely minecraft will work! STOP NOW, get a clean copy and try again!
2023-01-23 16:10:09 [SEVERE] [Forestry] ic2.core.IC2 failed validation. Halting runtime for security reasons. Please replace your mods with untampered versions from the official download sites.

Solution

  1. Create a file named java.security inside the instance minecraft(.minecraft/minecraft) folder with the following content:

    jdk.certpath.disabledAlgorithms=MD2, MD5, SHA1 jdkCA & usage TLSServer, \
    RSA keySize < 1024, DSA keySize < 1024, EC keySize < 224, \
    include jdk.disabled.namedCurves

jdk.jar.disabledAlgorithms=MD2, MD5, RSA keySize < 1024, \
    DSA keySize < 1024, \
    include jdk.disabled.namedCurves

  2. Open Edit instance window

  3. Navigate to Java Setting

  4. Check the Java arguments checkbox

  5. Paste -Djava.security.properties=java.security inside the java arguments text box

Sources

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