Add some needed utilities for encryption

src/test/java/com/velocitypowered/proxy/util/EncryptionUtilsTest.java

@@ -0,0 +1,25 @@
+package com.velocitypowered.proxy.util;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+
+public class EncryptionUtilsTest {
+    @Test
+    public void twoComplementsSha1Digest() throws Exception {
+        String notchHash = hexDigest("Notch");
+        Assert.assertEquals("4ed1f46bbe04bc756bcb17c0c7ce3e4632f06a48", notchHash);
+
+        String jebHash = hexDigest("jeb_");
+        Assert.assertEquals("-7c9d5b0044c130109a5d7b5fb5c317c02b4e28c1", jebHash);
+    }
+
+    private String hexDigest(String str) throws Exception {
+        MessageDigest digest = MessageDigest.getInstance("SHA-1");
+        digest.update(str.getBytes(StandardCharsets.UTF_8));
+        byte[] digested = digest.digest();
+        return EncryptionUtils.twoComplementsSha1Digest(digested);
+    }
+}