How to replace the SecretKeyFactory.getInstance(“Some String”) with a file source

Question

I am using SecretKeyFactory.getInstance("some String") to encrypt/dycrypt a string.But I am using SecretKeyFactory.getInstance("some String") as the key , but I need to use the String key from a file name and that file instance I need to pass inside the SecretKeyFactory.getInstance() method which I can't do.

  SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");// here i need to replace
  SecretKeyFactory factory = SecretKeyFactory.getInstance(keyFis.toString());
  char[] password = "Pass@word1".toCharArray();
  byte[] salt = "S@1tS@1t".getBytes("UTF-8");

  KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);
  SecretKey tmp = factory.generateSecret(spec);
  byte[] encoded = tmp.getEncoded();
  return new SecretKeySpec(encoded, "AES");

I am doing

  // reading the key 
  String fileName = "C://somewhere//aesKey.dat";
  FileInputStream keyFis = new FileInputStream(fileName);
  byte[] encKey = new byte[keyFis.available()];
  keyFis.read(encKey);
  keyFis.close();

  SecretKeyFactory factory = SecretKeyFactory.getInstance(keyFis.toString());
  char[] password = "Pass@word1".toCharArray();
  byte[] salt = "S@1tS@1t".getBytes("UTF-8");

  KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);
  SecretKey tmp = factory.generateSecret(spec);
  byte[] encoded = tmp.getEncoded();
  return new SecretKeySpec(encoded, "AES");

But I am getting below exception

Exception in thread "main" java.security.NoSuchAlgorithmException: java.io.FileInputStream@5ea75ea7 SecretKeyFactory not available
at javax.crypto.SecretKeyFactory.<init>(Unknown Source)
at javax.crypto.SecretKeyFactory.getInstance(Unknown Source)
at test.Main.generateKey(Main.java:66)
at test.Main.getCipher(Main.java:42)
at test.Main.Encrypt(Main.java:30)
at test.Main.main(Main.java:21)

How to solve this

Answer 1

If C:\\\\somewhere\\\\aesKey.dat contains the AES key, then you can read the file into a byte[] and directly create a Key from that, because a SecretKeySpec implements the Key interface.

String fileName = "C:\\somewhere\\aesKey.dat";
byte[] encoded = Files.readAllBytes(Paths.get(fileName));
return new SecretKeySpec(encoded, "AES");

Make sure that you import java.nio.file.* .

---

Never use FileInputStream#available to determine the size of the file. The returned size can be smaller than the actual file, because the reader is buffered.