Exception on download: sun.security.validator.Vali

I'm trying to use sbt on Ubuntu 16.04, but am getting errors when trying to run it. I did a fresh install, then followed the directions exactly from the sbt site, but get the following when I do sbt:

Getting org.scala-sbt sbt 0.13.12 ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/main/0.13.12/jars/main.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/compiler-interface/0.13.12/jars/compiler-interface.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/actions/0.13.12/jars/actions.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/main-settings/0.13.12/jars/main-settings.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/io/0.13.12/jars/io.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/ivy/0.13.12/jars/ivy.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/command/0.13.12/jars/command.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/completion/0.13.12/jars/completion.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/api/0.13.12/jars/api.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/collections/0.13.12/jars/collections.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/incremental-compiler/0.13.12/jars/incremental-compiler.jar ...
downloading https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/compile/0.13.12/jars/compile.jar ...

:: problems summary ::
:::: WARNINGS
        [FAILED     ] org.scala-sbt#main;0.13.12!main.jar: sun.security.validator.ValidatorException: No trusted certificate found (1180ms)

        [FAILED     ] org.scala-sbt#main;0.13.12!main.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/main/0.13.12/jars/main.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/main/0.13.12/main-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/main/0.13.12/jars/main.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/main/0.13.12/jars/main.jar

        [FAILED     ] org.scala-sbt#compiler-interface;0.13.12!compiler-interface.jar: sun.security.validator.ValidatorException: No trusted certificate found (577ms)

        [FAILED     ] org.scala-sbt#compiler-interface;0.13.12!compiler-interface.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/compiler-interface/0.13.12/jars/compiler-interface.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/compiler-interface/0.13.12/compiler-interface-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/compiler-interface/0.13.12/jars/compiler-interface.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/compiler-interface/0.13.12/jars/compiler-interface.jar

        [FAILED     ] org.scala-sbt#actions;0.13.12!actions.jar: sun.security.validator.ValidatorException: No trusted certificate found (569ms)

        [FAILED     ] org.scala-sbt#actions;0.13.12!actions.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/actions/0.13.12/jars/actions.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/actions/0.13.12/actions-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/actions/0.13.12/jars/actions.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/actions/0.13.12/jars/actions.jar

        [FAILED     ] org.scala-sbt#main-settings;0.13.12!main-settings.jar: sun.security.validator.ValidatorException: No trusted certificate found (666ms)

        [FAILED     ] org.scala-sbt#main-settings;0.13.12!main-settings.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/main-settings/0.13.12/jars/main-settings.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/main-settings/0.13.12/main-settings-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/main-settings/0.13.12/jars/main-settings.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/main-settings/0.13.12/jars/main-settings.jar

        [FAILED     ] org.scala-sbt#io;0.13.12!io.jar: sun.security.validator.ValidatorException: No trusted certificate found (597ms)

        [FAILED     ] org.scala-sbt#io;0.13.12!io.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/io/0.13.12/jars/io.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/io/0.13.12/io-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/io/0.13.12/jars/io.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/io/0.13.12/jars/io.jar

        [FAILED     ] org.scala-sbt#ivy;0.13.12!ivy.jar: sun.security.validator.ValidatorException: No trusted certificate found (644ms)

        [FAILED     ] org.scala-sbt#ivy;0.13.12!ivy.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/ivy/0.13.12/jars/ivy.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/ivy/0.13.12/ivy-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/ivy/0.13.12/jars/ivy.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/ivy/0.13.12/jars/ivy.jar

        [FAILED     ] org.scala-sbt#command;0.13.12!command.jar: sun.security.validator.ValidatorException: No trusted certificate found (762ms)

        [FAILED     ] org.scala-sbt#command;0.13.12!command.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/command/0.13.12/jars/command.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/command/0.13.12/command-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/command/0.13.12/jars/command.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/command/0.13.12/jars/command.jar

        [FAILED     ] org.scala-sbt#completion;0.13.12!completion.jar: sun.security.validator.ValidatorException: No trusted certificate found (594ms)

        [FAILED     ] org.scala-sbt#completion;0.13.12!completion.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/completion/0.13.12/jars/completion.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/completion/0.13.12/completion-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/completion/0.13.12/jars/completion.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/completion/0.13.12/jars/completion.jar

        [FAILED     ] org.scala-sbt#api;0.13.12!api.jar: sun.security.validator.ValidatorException: No trusted certificate found (585ms)

        [FAILED     ] org.scala-sbt#api;0.13.12!api.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/api/0.13.12/jars/api.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/api/0.13.12/api-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/api/0.13.12/jars/api.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/api/0.13.12/jars/api.jar

        [FAILED     ] org.scala-sbt#collections;0.13.12!collections.jar: sun.security.validator.ValidatorException: No trusted certificate found (568ms)

        [FAILED     ] org.scala-sbt#collections;0.13.12!collections.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/collections/0.13.12/jars/collections.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/collections/0.13.12/collections-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/collections/0.13.12/jars/collections.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/collections/0.13.12/jars/collections.jar

        [FAILED     ] org.scala-sbt#incremental-compiler;0.13.12!incremental-compiler.jar: sun.security.validator.ValidatorException: No trusted certificate found (672ms)

        [FAILED     ] org.scala-sbt#incremental-compiler;0.13.12!incremental-compiler.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/incremental-compiler/0.13.12/jars/incremental-compiler.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/incremental-compiler/0.13.12/incremental-compiler-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/incremental-compiler/0.13.12/jars/incremental-compiler.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/incremental-compiler/0.13.12/jars/incremental-compiler.jar

        [FAILED     ] org.scala-sbt#compile;0.13.12!compile.jar: sun.security.validator.ValidatorException: No trusted certificate found (587ms)

        [FAILED     ] org.scala-sbt#compile;0.13.12!compile.jar:  (0ms)

    ==== local: tried

      /home/james/.ivy2/local/org.scala-sbt/compile/0.13.12/jars/compile.jar

    ==== Maven Central: tried

      https://repo1.maven.org/maven2/org/scala-sbt/compile/0.13.12/compile-0.13.12.jar

    ==== typesafe-ivy-releases: tried

      https://repo.typesafe.com/typesafe/ivy-releases/org.scala-sbt/compile/0.13.12/jars/compile.jar

    ==== sbt-ivy-snapshots: tried

      https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.scala-sbt/compile/0.13.12/jars/compile.jar

        ::::::::::::::::::::::::::::::::::::::::::::::

        ::              FAILED DOWNLOADS            ::

        :: ^ see resolution messages for details  ^ ::

        ::::::::::::::::::::::::::::::::::::::::::::::

        :: org.scala-sbt#main;0.13.12!main.jar

        :: org.scala-sbt#actions;0.13.12!actions.jar

        :: org.scala-sbt#io;0.13.12!io.jar

        :: org.scala-sbt#completion;0.13.12!completion.jar

        :: org.scala-sbt#collections;0.13.12!collections.jar

        :: org.scala-sbt#api;0.13.12!api.jar

        :: org.scala-sbt#incremental-compiler;0.13.12!incremental-compiler.jar

        :: org.scala-sbt#compile;0.13.12!compile.jar

        :: org.scala-sbt#ivy;0.13.12!ivy.jar

        :: org.scala-sbt#main-settings;0.13.12!main-settings.jar

        :: org.scala-sbt#command;0.13.12!command.jar

        :: org.scala-sbt#compiler-interface;0.13.12!compiler-interface.jar

        ::::::::::::::::::::::::::::::::::::::::::::::



:: USE VERBOSE OR DEBUG MESSAGE LEVEL FOR MORE DETAILS
download failed: org.scala-sbt#main;0.13.12!main.jar
download failed: org.scala-sbt#actions;0.13.12!actions.jar
download failed: org.scala-sbt#io;0.13.12!io.jar
download failed: org.scala-sbt#completion;0.13.12!completion.jar
download failed: org.scala-sbt#collections;0.13.12!collections.jar
download failed: org.scala-sbt#api;0.13.12!api.jar
download failed: org.scala-sbt#incremental-compiler;0.13.12!incremental-compiler.jar
download failed: org.scala-sbt#compile;0.13.12!compile.jar
download failed: org.scala-sbt#ivy;0.13.12!ivy.jar
download failed: org.scala-sbt#main-settings;0.13.12!main-settings.jar
download failed: org.scala-sbt#command;0.13.12!command.jar
download failed: org.scala-sbt#compiler-interface;0.13.12!compiler-interface.jar
Error during sbt execution: Error retrieving required libraries
  (see /home/james/.sbt/boot/update.log for complete log)
Error: Could not retrieve sbt 0.13.12

I'm not sure what would be causing this. I also tried sudo sbt, which made no difference (in case it was a permissions error). I should note that some downloads succeed.

Edit:

Here's some proof I'm doing it right:

On Ubuntu, when you have the package openjdk-9-jre-headless installed, sbt can't verify its downloads because they're not signed against the OpenJDK 9 certificates. To fix this, you need to uninstall OpenJDK 9:

$ apt-get remove openjdk-9-*

Then make sure you have openjdk-8-jre-headless installed, and use update-java-alternatives to select it as the default JRE (see https://askubuntu.com/a/731862/459610 for details).

Answer found at https://medium.com/@henricook/solution-to-sun-security-validator-validatorexception-e300dd7dba70#.wn7uh2z9q

(Note: I'm not on an Ubuntu machine now, so I can't verify this, but: you may be able to get away with just setting the default Java to JDK 8.)