How to Encrypt or Decrypt a File in Java?

Question

I want to encrypt and decrypt a file in java, i had read this url http://www-users.york.ac.uk/~mal503/lore/pkencryption.htm and i got two files namely public Security certificate and private security certificate file and private.pem file, i copied these files and pasted in the current directory and worte java code as follows, when i run this no encryption or decryption is performed, pls see this and tell me where i went wrong

Encrypt Code

File ecryptfile=new File("encrypt data");
                File publickeydata=new File("/publickey");
                File encryptmyfile=new File("/sys_data.db");
                File copycontent =new File("Copy Data");
                secure.makeKey();
                secure.saveKey(ecryptfile, publickeydata);
                secure.encrypt(encryptmyfile, copycontent);

Decrypt code

File ecryptfile=new File("encrypt data");
                File privateKeyFile=new File("/privatekey");
                File encryptmyfile=new File("/sys_data.db");
                File unencryptedFile =new File("unencryptedFile");
                try {
                                secure.loadKey(encryptmyfile, privateKeyFile);
                                secure.decrypt(encryptmyfile, unencryptedFile);
                        } catch (GeneralSecurityException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                        } catch (IOException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                        }

Answer 1

You simply have muddled your files. This code works using the DER files generated from openssl as described in the article you linked:

    FileEncryption secure = new FileEncryption();

    // Encrypt code
    {
        File encryptFile = new File("encrypt.data");
        File publicKeyData = new File("public.der");
        File originalFile = new File("sys_data.db");
        File secureFile = new File("secure.data");

        // create AES key
        secure.makeKey();

        // save AES key using public key
        secure.saveKey(encryptFile, publicKeyData);

        // save original file securely 
        secure.encrypt(originalFile, secureFile);
    }

    // Decrypt code
    {
        File encryptFile = new File("encrypt.data");
        File privateKeyFile = new File("private.der");
        File secureFile = new File("secure.data");
        File unencryptedFile = new File("unencryptedFile");

        // load AES key
        secure.loadKey(encryptFile, privateKeyFile);

        // decrypt file
        secure.decrypt(secureFile, unencryptedFile);
    }

Answer 2

Here is the Simplest Piece of Code for encrypting a document with any Key(Here Random Key)

randomKey = randomKey.substring(0, 16);
        keyBytes = randomKey.getBytes();
        key = new SecretKeySpec(keyBytes, "AES");
        paramSpec = new IvParameterSpec(iv);
        ecipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
        in = new FileInputStream(srcFile);
        out = new FileOutputStream(encryptedFile);
        out = new CipherOutputStream(out, ecipher);
        int numRead = 0;
        while ((numRead = in.read(buf)) >= 0) {
            out.write(buf, 0, numRead);
        }
        in.close();
        out.flush();
        out.close();