Use shared SecureRandom

nostr-java-util/src/main/java/nostr/util/NostrUtil.java

@@ -17,6 +17,7 @@
 public class NostrUtil {
 
     private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
+    private static final SecureRandom RANDOM = new SecureRandom();
 
     public static String bytesToHex(byte[] b) {
         char[] hexChars = new char[b.length * 2];
@@ -98,7 +99,7 @@ public static byte[] xor(byte[] b0, byte[] b1) {
 
     public static byte[] createRandomByteArray(int len) {
         byte[] b = new byte[len];
-        new SecureRandom().nextBytes(b);
+        RANDOM.nextBytes(b);
         return b;
     }
 

nostr-java-util/src/test/java/nostr/util/NostrUtilRandomTest.java

@@ -0,0 +1,25 @@
+package nostr.util;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class NostrUtilRandomTest {
+
+    @Test
+    public void testCreateRandomByteArrayLength() {
+        int len = 16;
+        byte[] data = NostrUtil.createRandomByteArray(len);
+        assertNotNull(data, "Random byte array should not be null");
+        assertEquals(len, data.length, "Random byte array has wrong length");
+    }
+
+    @Test
+    public void testCreateRandomByteArrayUniqueness() {
+        byte[] data1 = NostrUtil.createRandomByteArray(16);
+        byte[] data2 = NostrUtil.createRandomByteArray(16);
+        assertFalse(Arrays.equals(data1, data2), "Consecutive random arrays should differ");
+    }
+}