Help with RSA Encryption using SATSA

Question

Hello,
I am a new to writing code on J2ME . I am trying to encrypt data using
RSA public key on J2ME using SATSA.
I generated the public key using openssl in the PEM format and stored the
key (mypublickey) as a Base64 decoded byte array in my code.
Next, I did the following:
X509EncodedKeySpec test - new X509EncodedKeySpec(mypublickey);
KeyFactory kf = KeyFactory.getInstance("RSA");
PublicKey key = kf.generatePublic(test);
I used this key to encrypt as follows:
cipher c = Cipher.getInstance("RSA");
c.init(Cipher.ENCRYPT_MODE, key);
c.doFinal(data,0,data.length,ciphertext,0);
where byte[] data = "1234567890".getBytes();
I get no errors during this process.
Now, when I try to decrypt the string, I get a padding error as follows:
javax.crypto.BadPaddingException: Data must start with zero
The decode is done on a server.
I tried getting an instance of the cipher with RSA/ECB/NoPadding and this time the decrypt gives junk.
Question 2: The SATSA example online at http://java.sun.com/j2me/docs/satsa-dg/AppD.html
has a public key embedded as a byte array. They haven't explained how
this key is generated. Does someone know?
Question 3: Suppose, I can get the modulus and exponent of the public key is there any way I can convert it to X509EncodedKeySpec so that I can
use the APIs in SATSA?
Thanks in advance for your help. I have been trying to solve this for a lot of time and any help will be greatly appreciated.

Answer 1

Just wanted to add my code:
public class test2 {
     public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException, ShortBufferException {
          // TODO Auto-generated method stub
          byte [] data = "012345678901234567890123456789ab".getBytes();
          Base64 base64 = new Base64();
/*public key generated by
          byte [] mypublickey = base64.decode("publickey in PEM format");
          byte [] ciphertext = new byte[128];
          X509EncodedKeySpec test = new X509EncodedKeySpec(mypublickey);
          byte [] myprivatekey = base64.decode("privatekey in pkcs8format");
KeyFactory rsakeyfac = KeyFactory.getInstance("RSA");
          PublicKey pubkey = rsakeyfac.generatePublic(test);
          Cipher c1 = Cipher.getInstance("RSA");
          c1.init(Cipher.ENCRYPT_MODE, pubkey);
          c1.doFinal(data, 0,data.length, ciphertext);
          PKCS8EncodedKeySpec pks2 = new PKCS8EncodedKeySpec(myprivatekey);
          RSAPrivateCrtKey privkey = (RSAPrivateCrtKey)rsakeyfac.generatePrivate(pks2);
          Cipher c2 = Cipher.getInstance("RSA");
          c2.init(Cipher.DECRYPT_MODE, privkey);
          byte [] decrypteddata = c2.doFinal(ciphertext);
          System.out.println("Decrypted String is:"+new String(decrypteddata).trim());
Error that I get is:
Exception in thread "main" javax.crypto.BadPaddingException: Data must start with zero
     at sun.security.rsa.RSAPadding.unpadV15(Unknown Source)
     at sun.security.rsa.RSAPadding.unpad(Unknown Source)
     at com.sun.crypto.provider.RSACipher.a(DashoA13*..)
     at com.sun.crypto.provider.RSACipher.engineDoFinal(DashoA13*..)
     at javax.crypto.Cipher.doFinal(DashoA13*..)