Add constructors for PGPPadding class

pg/src/main/java/org/bouncycastle/openpgp/PGPPadding.java

@@ -1,10 +1,12 @@
 package org.bouncycastle.openpgp;
 
 import java.io.IOException;
+import java.security.SecureRandom;
 
 import org.bouncycastle.bcpg.BCPGInputStream;
 import org.bouncycastle.bcpg.Packet;
 import org.bouncycastle.bcpg.PaddingPacket;
+import org.bouncycastle.crypto.CryptoServicesRegistrar;
 
 /**
  * The PGPPadding contains random data, and can be used to defend against traffic analysis on version 2 SEIPD messages
@@ -16,10 +18,25 @@ public class PGPPadding
 {
     private PaddingPacket p;
 
+    /**
+     * Minimum random padding length in octets.
+     * Chosen totally arbitrarily.
+     */
+    public static final int MIN_PADDING_LEN = 16;
+
+    /**
+     * Maximum random padding length.
+     * Chosen somewhat arbitrarily, as SSH also uses max 255 bytes for random padding.
+     *
+     * @see <a href="https://www.rfc-editor.org/rfc/rfc4253.html#section-6">
+     *     rfc4253 - Binary Packet Protocol</a>
+     */
+    public static final int MAX_PADDING_LEN = 255;
+
     /**
      * Default constructor.
      *
-     * @param in
+     * @param in packet input stream
      * @throws IOException
      */
     public PGPPadding(
@@ -34,6 +51,53 @@ public PGPPadding(
         p = (PaddingPacket)packet;
     }
 
+    /**
+     * Generate a new, random {@link PGPPadding} object.
+     * The padding consists of n random bytes, where n is a number between (inclusive) {@link #MIN_PADDING_LEN}
+     * and {@link #MAX_PADDING_LEN}.
+     */
+    public PGPPadding()
+    {
+        this(CryptoServicesRegistrar.getSecureRandom());
+    }
+
+    /**
+     * Generate a new, random {@link PGPPadding} object.
+     * The padding consists of n random bytes, where n is a number between (inclusive) {@link #MIN_PADDING_LEN}
+     * and {@link #MAX_PADDING_LEN}.
+     *
+     * @param random random number generator instance
+     */
+    public PGPPadding(SecureRandom random)
+    {
+        this(MIN_PADDING_LEN + random.nextInt(MAX_PADDING_LEN - MIN_PADDING_LEN + 1), random);
+    }
+
+    /**
+     * Generate a new, random {@link PGPPadding} object.
+     * The padding consists of <pre>len</pre> random bytes.
+     */
+    public PGPPadding(int len)
+    {
+        this(len, CryptoServicesRegistrar.getSecureRandom());
+    }
+
+    /**
+     * Generate a new, random {@link PGPPadding} object.
+     * The padding consists of <pre>len</pre> random bytes.
+     *
+     * @param len number of random octets
+     * @param random random number generator instance
+     */
+    public PGPPadding(int len, SecureRandom random)
+    {
+        this.p = new PaddingPacket(len, random);
+    }
+
+    /**
+     * Return the padding octets as a byte array.
+     * @return padding octets
+     */
     public byte[] getPadding()
     {
         return p.getPadding();