title: javax.crypto.BadPaddingException: data hash wrong
body: <p>I try to write a crypto package in java that wraps the javax.crypto package and makes it more comfortable to use. So I implemented a RSACore class that only wraps javax.crypto. Then I implemented two classes RSAEncoder and RSADecoder to hide tha javax.crypto.Cipher and initiation of it.</p>
  
  <p>Now to my problem:
  I have written some small tests for RSACore, RSAEncoder and RSADecoder.
  All tests work fine except the decoder's one. I get everytime the BadPaddingException when I call the dofinal() on the encoded data.
  I googled for it and find in most cases it has to do with wrong keys but I am sure I only generate one pair and work on it. I do not know where to search the error.
  As provider I use bouncycastle because with JCE I got an error that signing is not possible with OAEP
  Here is the complete errormessage:</p>
  
  <pre><code>javax.crypto.BadPaddingException: data hash wrong
  at org.bouncycastle.jcajce.provider.asymmetric.rsa.CipherSpi.engineDoFinal(Unknown Source)
  at javax.crypto.Cipher.doFinal(Cipher.java:2145)
  at de.coding.crypto.rsa.RSACore.doFinal(RSACore.java:178)
  at de.coding.crypto.rsa.RSADecoder.doFinal(RSADecoder.java:59)
  at de.coding.crypto.interfaces.AbstractDecoder.doFinal(AbstractDecoder.java:49)
  at de.coding.crypto.rsa.RSADecoderTest.test(RSADecoderTest.java:21)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
  at java.lang.reflect.Method.invoke(Unknown Source)
  at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
  at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
  at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
  at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
  at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
  at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
  at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
  at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
  at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
  at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
  at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
  at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
  at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
  at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
  at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
  </code></pre>
  
  <p>here is the test:</p>
  
  <pre><code>package de.coding.crypto.rsa;
  
  import static org.junit.Assert.*;
  
  import java.security.KeyPair;
  
  import org.junit.Test;
  
  public class RSADecoderTest
  {
      @Test
      public void test()
      {
          try
          {
              KeyPair kp = RSACore.generateKeys();
              String str = "Hello world! This is me. Life should be fun for everyone.";
              RSAEncoder encoder = new RSAEncoder(kp.getPublic());
              byte[] encoded = encoder.doFinal(str.getBytes());
              RSADecoder decoder = new RSADecoder(kp.getPrivate());
              byte[] decoded = decoder.doFinal(encoded);//&lt;-------------------BadPaddingException
              assertTrue(str.getBytes().length == decoded.length);
              int size = decoded.length;
              for (int i=0; i&lt;size; i++)
              {
                  assertTrue(decoded[i] == str.getBytes()[i]);
              }
          }
          catch (Exception e)
          {
              fail();
          }
      }
  }
  </code></pre>
  
  <p>Do you see there any logical error?
  I also can post encoder, decoder and core but that are plenty of lines.
  Thank you for reading and helping!</p>
  
  <p>RSAEncoder:</p>
  
  <pre><code>public RSAEncoder(PublicKey key) throws InvalidKeyException
  {
      super();
      cipher = RSACore.initEncodeMode(key);
  }
  
  public byte[] doFinal()
  {
      try
      {
          buffer.add(RSACore.doFinal(cipher));//buffer is a LinkedList&lt;byte[]&gt;
          return clearBuffer();
      }
      catch (IllegalBlockSizeException e)
      {
          throw new RuntimeException(e);
      }
      catch (BadPaddingException e)
      {
          throw new RuntimeException(e);
      }
  }
  
  protected byte[] clearBuffer()
  {
      byte[] ret = new byte[getBufferSize()];
      int index = 0;
      for (byte[] b : buffer)
      {
          if (b != null)
          {
              for (int i=0; i&lt;b.length; i++)
              {
                  ret[index] = b[i];
              }
          }
      }
      buffer.clear();
      return ret;
  }
  
  public byte[] doFinal(byte[] b, int offset, int length)
  {
      if (length &gt; RSACore.KEYSIZE-11)
      {
          update(b, offset, length);
          return doFinal();
      }
      else
      {
          try
          {
              buffer.add(RSACore.doFinal(cipher, b, offset, length));
              return clearBuffer();
          }
          catch (IllegalBlockSizeException e)
          {
              throw new RuntimeException(e);
          }
          catch (BadPaddingException e)
          {
              throw new RuntimeException(e);
          }
      }
  }
  </code></pre>
  
  <p>RSADecoder (same except condtructor):</p>
  
  <pre><code>public RSADecoder(PrivateKey key) throws InvalidKeyException
  {
      cipher = RSACore.initDecodeMode(key);
  }
  </code></pre>
  
  <p>RSACore:</p>
  
  <pre><code>public byte[] doFinal(byte[] b)
  {
      return doFinal(b, 0, b.length);
  }
  
  public static byte[] doFinal(Cipher cipher, byte[] msg, int offset, int length) throws IllegalBlockSizeException, BadPaddingException
  {
      byte[] ret = cipher.doFinal(msg, offset, length);
      if (ret == null)
      {
          return new byte[0];
      }
      return ret;
  }
  
  public static Cipher initEncodeMode(Key key) throws InvalidKeyException
  {
      try
      {
          Cipher cipher = Cipher.getInstance(ALGORITHMDETAIL, PROVIDER);
          cipher.init(Cipher.ENCRYPT_MODE, key);
          return cipher;
      }
      catch (NoSuchAlgorithmException e)
      {
          throw new RuntimeException(e);
      }
      catch (NoSuchPaddingException e)
      {
          throw new RuntimeException(e);
      }
      catch (NoSuchProviderException e)
      {
          throw new RuntimeException(e);
      }
  }
  
  public static Cipher initDecodeMode(Key key) throws InvalidKeyException
  {
      try
      {
          Cipher cipher = Cipher.getInstance(ALGORITHMDETAIL, PROVIDER);
          cipher.init(Cipher.DECRYPT_MODE, key);
          return cipher;
      }
      catch (NoSuchAlgorithmException e)
      {
          throw new RuntimeException(e);
      }
      catch (NoSuchPaddingException e)
      {
          throw new RuntimeException(e);
      }
      catch (NoSuchProviderException e)
      {
          throw new RuntimeException(e);
      }
  }
  </code></pre>