Dazed and confused by Java Security & BouncyCastle APIs

Question

I\'ve been trying to make sense of the BouncyCastle cryptography APIs for Java. Unfortunately, I\'m finding Java cryptography in general to be so obscured by service provider in

Answer 1

import java.security.GeneralSecurityException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;

import javax.crypto.Cipher;

public class RSACrypto
{

  /* A 1024-bit key will encrypt messages up to 117 bytes long. */
  private static final int KEY_SIZE = 1024;

  private static final String XFORM = 
    "RSA/ECB/OAEPWITHSHA-256ANDMGF1PADDING";

  public static KeyPair generateRSAKeyPair()
    throws GeneralSecurityException
  {
    KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");
    gen.initialize(KEY_SIZE);
    return gen.generateKeyPair();
  }

  public static byte[] encrypt(byte[] plaintext, PublicKey pub)
    throws GeneralSecurityException
  {
    Cipher cipher = Cipher.getInstance(XFORM);
    cipher.init(Cipher.ENCRYPT_MODE, pub);
    return cipher.doFinal(plaintext);
  }

  public static byte[] decrypt(byte[] ciphertext, PrivateKey pvt)
    throws GeneralSecurityException
  {
    Cipher cipher = Cipher.getInstance(XFORM);
    cipher.init(Cipher.DECRYPT_MODE, pvt);
    return cipher.doFinal(ciphertext);
  }

  public static void main(String... argv)
    throws Exception
  {
    KeyPair pair = RSACrypto.generateRSAKeyPair();
    byte[] plaintext = "A short secret message.".getBytes("UTF-8");
    byte[] ciphertext = RSACrypto.encrypt(plaintext, pair.getPublic());
    byte[] recovered = RSACrypto.decrypt(ciphertext, pair.getPrivate());
    System.out.println(new String(recovered, "UTF-8"));
  }

}