StreamWriteSizeDemo.java

package com.qozix.crypto;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.SecureRandom;

public class BlockTests3 {

  private byte[] mKey = new byte[16];
  private byte[] mIv = new byte[16];

  {
    SecureRandom secureRandom = new SecureRandom();
    secureRandom.nextBytes(mIv);
    secureRandom.nextBytes(mKey);
  }

  private byte[] mMessage = new byte[50];
  {
    for(int i = 0; i < mMessage.length; i++) {
      mMessage[i] = (byte) (i + 1);
    }
  }

  SecretKeySpec mKeySpec;
  IvParameterSpec mIvSpec;

  private Cipher mEncryptionCipher;
  private Cipher mDecryptionCipher;

  public BlockTests3() throws Exception {

    mKeySpec = new SecretKeySpec(mKey, "AES");
    mIvSpec = new IvParameterSpec(mIv);

    mEncryptionCipher = Cipher.getInstance("AES/CTR/NoPadding");
    mDecryptionCipher = Cipher.getInstance("AES/CTR/NoPAdding");

    mEncryptionCipher.init(Cipher.ENCRYPT_MODE, mKeySpec, mIvSpec);
    mDecryptionCipher.init(Cipher.DECRYPT_MODE, mKeySpec, mIvSpec);

    System.out.println("clear");
    printBytes(mMessage);

    System.out.println("encryptMessage");
    mMessage = encryptMessage(mMessage);
    printBytes(mMessage);

    System.out.println("decryptMessage");
    mMessage = decryptMessage(mMessage);
    printBytes(mMessage);

    System.out.println();
    System.out.println("Done.");
  }

  private byte[] encryptMessage(byte[] input) throws IOException {
    ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(input);
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    CipherOutputStream cipherOutputStream = new CipherOutputStream(byteArrayOutputStream, mEncryptionCipher);
    int size = byteArrayInputStream.available();
    int bytesRead;
    byte[] buffer = new byte[mEncryptionCipher.getBlockSize()];
    while((bytesRead = byteArrayInputStream.read(buffer, 0, buffer.length)) > -1) {
      cipherOutputStream.write(buffer, 0, Math.min(buffer.length, bytesRead));
    }
    return byteArrayOutputStream.toByteArray();
  }

  private byte[] decryptMessage(byte[] encrypted) throws IOException {
    ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(encrypted);
    CipherInputStream cipherInputStream = new CipherInputStream(byteArrayInputStream, mDecryptionCipher);
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    int bytesRead;
    byte[] buffer = new byte[mDecryptionCipher.getBlockSize()];
    while((bytesRead = cipherInputStream.read(buffer, 0, buffer.length)) > -1) {
      byteArrayOutputStream.write(buffer, 0, Math.min(bytesRead, buffer.length));
    }
    return byteArrayOutputStream.toByteArray();
  }

  private void printBytes(byte[] bytes) {
    for(byte b : bytes) {
      System.out.print(printByte(b) + ",");
    }
    System.out.println();
  }

  private String printByte(byte b) {
    int intValue = (int) b;
    String stringValue = String.valueOf(intValue);
    while(stringValue.length() < 4) {
      stringValue = " " + stringValue;
    }
    return stringValue;
  }

}