diff --git a/external-sop/src/test/java/sop/external/JUtils.java b/external-sop/src/test/java/sop/external/JUtils.java
index d0d1601..38a5829 100644
--- a/external-sop/src/test/java/sop/external/JUtils.java
+++ b/external-sop/src/test/java/sop/external/JUtils.java
@@ -12,10 +12,25 @@ import static org.junit.jupiter.api.Assertions.fail;
 
 public class JUtils {
 
+    /**
+     * Return true, if the given <pre>array</pre> starts with <pre>start</pre>.
+     *
+     * @param array array
+     * @param start start
+     * @return true if array starts with start, false otherwise
+     */
     public static boolean arrayStartsWith(byte[] array, byte[] start) {
         return arrayStartsWith(array, start, 0);
     }
 
+    /**
+     * Return true, if the given <pre>array</pre> contains the given <pre>start</pre> at offset <pre>offset</pre>.
+     *
+     * @param array array
+     * @param start start
+     * @param offset offset
+     * @return true, if array contains start at offset, false otherwise
+     */
     public static boolean arrayStartsWith(byte[] array, byte[] start, int offset) {
         if (offset < 0) {
             throw new IllegalArgumentException("Offset cannot be negative");
@@ -33,6 +48,12 @@ public class JUtils {
         return true;
     }
 
+    /**
+     * Assert that the given <pre>array</pre> starts with <pre>start</pre>.
+     *
+     * @param array array
+     * @param start start
+     */
     public static void assertArrayStartsWith(byte[] array, byte[] start) {
         if (!arrayStartsWith(array, start)) {
             byte[] actual = new byte[Math.min(start.length, array.length)];
@@ -43,6 +64,13 @@ public class JUtils {
         }
     }
 
+    /**
+     * Assert that the given <pre>array</pre> contains <pre>start</pre> at <pre>offset</pre>.
+     *
+     * @param array array
+     * @param start start
+     * @param offset offset
+     */
     public static void assertArrayStartsWith(byte[] array, byte[] start, int offset) {
         if (!arrayStartsWith(array, start, offset)) {
             byte[] actual = new byte[Math.min(start.length, array.length - offset)];
@@ -53,6 +81,12 @@ public class JUtils {
         }
     }
 
+    /**
+     * Assert equality of the given two ascii armored byte arrays, ignoring armor header lines.
+     *
+     * @param first first ascii armored bytes
+     * @param second second ascii armored bytes
+     */
     public static void assertAsciiArmorEquals(byte[] first, byte[] second) {
         byte[] firstCleaned = removeArmorHeaders(first);
         byte[] secondCleaned = removeArmorHeaders(second);
@@ -60,6 +94,13 @@ public class JUtils {
         assertArrayEquals(firstCleaned, secondCleaned);
     }
 
+    /**
+     * Remove armor headers "Comment:", "Version:", "MessageID:", "Hash:" and "Charset:" along with their values
+     * from the given ascii armored byte array.
+     *
+     * @param armor ascii armored byte array
+     * @return ascii armored byte array with header lines removed
+     */
     public static byte[] removeArmorHeaders(byte[] armor) {
         String string = new String(armor, StandardCharsets.UTF_8);
         string = string.replaceAll("Comment: .+\\R", "")