CODEWITHSUNDEEP
javapublic-keycryptoapi
MichBoy
MichBoy

Reputation: 299

java - get key from byte array

I have a java program that encrypts file content with a random-generated key. That key is encrpyted with RSA and saved into a text file.

Now, I have a java program that given the file and the keystore where the RSA key is stored, needs to first decrypt the encryped key and then with the key to decrypt the file.

Here's what I have so far:

// Fetch the other public key and decrypt the file encryption key
java.security.cert.Certificate cert2 = keystore.getCertificate("keyForSeckeyDecrypt");
Key secKeyPublicKey = cert2.getPublicKey();
Cipher cipher = Cipher.getInstance(secKeyPublicKey.getAlgorithm());
cipher.init(Cipher.DECRYPT_MODE, secKeyPublicKey);
keyFileFis = new FileInputStream(keyFile);
byte[] encryptedKey = new byte[128];
keyFileFis.read(encryptedKey);
byte[] realFileKey = cipher.doFinal(encryptedKey, 0, encryptedKey.length);
Key realKey = //  THE PROBLEM!!!;
keyFileFis.close();

In short, I get the encrypted key from the key text file and decrypt it, now I have the decrypted key as a byte array, how would I make it a Key variable again?

I've generated the key this way:

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
KeyGenerator keyGen = KeyGenerator.getInstance("AES");
Key secKey = keyGen.generateKey();
cipher.init(Cipher.ENCRYPT_MODE, secKey);

And encrypted it this way:

KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
KeyPair kp = kpg.genKeyPair();
PrivateKey privateKey = kp.getPrivate();
Cipher keyCipher = Cipher.getInstance("RSA");
keyCipher.init(Cipher.ENCRYPT_MODE, privateKey);
byte[] encryptedKey = keyCipher.doFinal(secKey.getEncoded());
FileOutputStream keyStream = new FileOutputStream("key.txt");
keyStream.write(encryptedKey);
keyStream.close();

Upvotes: 0

Views: 6090

Answers (2)

Akdeniz
Akdeniz

Reputation: 1270

If I get it right, this should work..

Key privateKey = keyStore.getKey("youralias", "password".toCharArray());
PublicKey publicKey = keyStore.getCertificate("youralias").getPublicKey();

KeyGenerator keyGen = KeyGenerator.getInstance("AES");
Key secKey = keyGen.generateKey();

Cipher keyCipher = Cipher.getInstance("RSA");
keyCipher.init(Cipher.ENCRYPT_MODE, privateKey);
byte[] encryptedKey = keyCipher.doFinal(secKey.getEncoded());

// Write & Read to/from file!

Cipher decryptCipher = Cipher.getInstance("RSA");
decryptCipher.init(Cipher.DECRYPT_MODE, publicKey);
byte[] decryptedKey = decryptCipher.doFinal(encryptedKey);

boolean equals = Arrays.equals(secKey.getEncoded(), new SecretKeySpec(decryptedKey, "AES").getEncoded());
System.out.println(equals?"Successfull!":"Failed!");

Upvotes: 0

micha
micha

Reputation: 49612

I haven't tried it but from clicking through the API SecretKeySpec could be what you are looking for.

SecretKeySpec(byte[] key, String algorithm)

It can be used to construct a SecretKey from a byte array, without having to go through a (provider-based) SecretKeyFactory.

This class is only useful for raw secret keys that can be represented as a byte array and have no key parameters associated with them, e.g., DES or Triple DES keys.

Upvotes: 1

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