RSA - Encrypt in Android / Decrypt in PHP

Question

I encrypt a word in java and I have trouble decrypting it in php.

here is how I create the keys in android:

public void GenerateAndSaveToFile(){
    try {

        KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
        kpg.initialize(1024);
        KeyPair kp = kpg.genKeyPair();
        Key publicKey = kp.getPublic();
        Key privateKey = kp.getPrivate();
        KeyFactory fact = KeyFactory.getInstance("RSA");
        RSAPublicKeySpec pub = fact.getKeySpec(kp.getPublic(), RSAPublicKeySpec.class);
        RSAPrivateKeySpec priv = fact.getKeySpec(kp.getPrivate(), RSAPrivateKeySpec.class);
        //////////////////////////
        String root = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).toString();
        File myDir = new File(root + "/keys");
        myDir.mkdirs();
        File file = new File (myDir, "private.key");
        FileOutputStream fileout1 = new FileOutputStream(file);
        ObjectOutputStream oout1 = new ObjectOutputStream(fileout1);
        oout1.writeObject(priv.getModulus());
        oout1.writeObject( priv.getPrivateExponent());
        oout1.close();
        ///////////////////////
        File file2 = new File (myDir, "public.key");
        FileOutputStream fileout2 = new FileOutputStream(file2);
        ObjectOutputStream oout2 = new ObjectOutputStream(new BufferedOutputStream(fileout2));
        oout2.writeObject(pub.getModulus());
        oout2.writeObject( pub.getPublicExponent());
        oout2.close();

    }
    catch (Exception ex){
        Exception e = ex;
    }

}

here is how I encrypt the word with generated public key in android:

byte[] u1Encrypted = RSAEncrypt(String.valueOf(inputEmail.getText()).getBytes());

 public byte[] RSAEncrypt(byte[] data) {
    try {
        PublicKey pubKey = ReadPublicKey();
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);
        byte[] cipherData = cipher.doFinal(data);
        return cipherData;
    }        
    catch (Exception ex)
    {
        Exception e = ex;
        return null;
    }

}


private PublicKey ReadPublicKey() throws IOException {
    try {
        AssetManager assetManager = getAssets();
        InputStream in = assetManager.open("public.key");
        ObjectInputStream oin = new ObjectInputStream(new BufferedInputStream(in));

        try {

            BigInteger m = (BigInteger) oin.readObject();
            BigInteger e = (BigInteger) oin.readObject();
            RSAPublicKeySpec keySpec = new RSAPublicKeySpec(m, e);
            KeyFactory fact = KeyFactory.getInstance("RSA");
            PublicKey pubKey = fact.generatePublic(keySpec);
            return pubKey;
        } catch (Exception e) {
            throw new RuntimeException("Spurious serialisation error", e);
        } finally {
            oin.close();
        }
    }
    catch (Exception ex)
    {
        Exception e = ex;
        return null;
    }
}

then I convert the encrypted string to base64 in android:

String u1EncryptedBase64 = Base64.encodeToString(u1Encrypted, Base64.DEFAULT);

and in php I decode the base64 string:

$encryptedString = base64_decode(u1EncryptedBase64);

get the private key:

$keytmp = fopen("../../../private.key", "r") or die("Unable to open file!");
$key = fread($keytmp,filesize("../../../private.key"));
$res = openssl_get_privatekey($key);

and finally I try to decrypt the string in php:

if (openssl_private_decrypt($encryptedString, $decrypted, $res)) {

    echo $decrypted;
}
else
{
    echo "problem";
}

and error I get is:

Warning: openssl_private_decrypt(): key parameter is not a valid private key ...

please guide me how to accompolish this task. thanks

RSA - Encrypt in Android / Decrypt in PHP

Answers (1)

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