Java – 対称鍵暗号の例

package com.techfou.symmetric;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;
import javax.swing.JOptionPane;

public class SymmetricKeyExample {
    private SecretKeySpec secretKey;
    private Cipher cipher;

    public SymmetricKeyExample(String secret, int length, String algorithm)
            throws UnsupportedEncodingException, NoSuchAlgorithmException, NoSuchPaddingException {
        byte[]key = new byte[length];
        key = fixSecret(secret, length);
        this.secretKey = new SecretKeySpec(key, algorithm);
        this.cipher = Cipher.getInstance(algorithm);
    }

    private byte[]fixSecret(String s, int length) throws UnsupportedEncodingException {
        if (s.length() < length) {
            int missingLength = length - s.length();
            for (int i = 0; i < missingLength; i++) {
                s += " ";
            }
        }
        return s.substring(0, length).getBytes("UTF-8");
    }

    public void encryptFile(File f)
            throws InvalidKeyException, IOException, IllegalBlockSizeException, BadPaddingException {
        System.out.println("Encrypting file: " + f.getName());
        this.cipher.init(Cipher.ENCRYPT__MODE, this.secretKey);
        this.writeToFile(f);
    }

    public void decryptFile(File f)
            throws InvalidKeyException, IOException, IllegalBlockSizeException, BadPaddingException {
        System.out.println("Decrypting file: " + f.getName());
        this.cipher.init(Cipher.DECRYPT__MODE, this.secretKey);
        this.writeToFile(f);
    }

    public void writeToFile(File f) throws IOException, IllegalBlockSizeException, BadPaddingException {
        FileInputStream in = new FileInputStream(f);
        byte[]input = new byte[(int) f.length()];
        in.read(input);

        FileOutputStream out = new FileOutputStream(f);
        byte[]output = this.cipher.doFinal(input);
        out.write(output);

        out.flush();
        out.close();
        in.close();
    }

    public static void main(String[]args) {
        File dir = new File("src/cryptodir");
        File[]filelist = dir.listFiles();

        SymmetricKeyExample ske;
        try {
            ske = new SymmetricKeyExample("!@#$MySecr3tPassw0rd", 16, "AES");

            int choice = -2;
            while (choice != -1) {
                String[]options = { "Encrypt All", "Decrypt All", "Exit" };
                choice = JOptionPane.showOptionDialog(null, "Select an option", "Options", 0,
                        JOptionPane.QUESTION__MESSAGE, null, options, options[0]);

                switch (choice) {
                case 0:
                    Arrays.asList(filelist).forEach(file -> {
                        try {
                            ske.encryptFile(file);
                        } catch (InvalidKeyException | IllegalBlockSizeException | BadPaddingException
                                | IOException e) {
                            System.err.println("Couldn't encrypt " + file.getName() + ": " + e.getMessage());
                        }
                    });
                    System.out.println("Files encrypted successfully");
                    break;
                case 1:
                    Arrays.asList(filelist).forEach(file -> {
                        try {
                            ske.decryptFile(file);
                        } catch (InvalidKeyException | IllegalBlockSizeException | BadPaddingException
                                | IOException e) {
                            System.err.println("Couldn't decrypt " + file.getName() + ": " + e.getMessage());
                        }
                    });
                    System.out.println("Files decrypted successfully");
                    break;
                default:
                    choice = -1;
                    break;
                }
            }
        } catch (UnsupportedEncodingException ex) {
            System.err.println("Couldn't create key: " + ex.getMessage());
        } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
            System.err.println(e.getMessage());
        }
    }
}

Encrypting file: Hello world.docx
Encrypting file: Hello world.pdf
Encrypting file: Smiley.png
Encrypting file: Text.txt
Files encrypted successfully

Decrypting file: Hello world.docx
Decrypting file: Hello world.pdf
Decrypting file: Smiley.png
Decrypting file: Text.txt
Files decrypted successfully

This is a text file.

‡(?ê?z@ou7ÿ—pø"é3.Õ0Ò;jVi¶‚