Only RSAPrivate (Crt) KeySpec and PKCS8EncodedKeySpec supported for RSA private keys

Question

I following the steps from the link : How to read .pem file to get private and public key. I executed the following three commands:

1. $openssl genrsa -out mykey.pem 2048
2. $openssl pkcs8 -topk8 -inform PEM -outform PEM -in mykey.pem -out private_key.pem -nocrypt
3. $ openssl rsa -in mykey.pem -pubout -outform DER -out public_key.der

This created three files, but when I was trying to read those through Java code I started facing below error:

PUBLIC KEY EXPO : 65537
Only RSAPrivate(Crt)KeySpec and PKCS8EncodedKeySpec supported for RSA private keys

My code for reference:

public class PublicPrivateKeyDemo {
    private static File privateKeyFile = null;
    private static File publicKeyFile = null;

    public static void main(String[] args) {
        String path = "C:/Users/test898/keys";
        privateKeyFile = new File(path + "/" + "private.pem");
        publicKeyFile = new File(path + "/" + "public.der");

        try {
            loadkeys();
        } catch (IOException | GeneralSecurityException e) {
            System.out.println(e.getMessage());
        }
    }

    private static void loadkeys() throws IOException, GeneralSecurityException {
        byte[] publicKeyBytes = new byte[(int) publicKeyFile.length()];
        FileInputStream publicFis = null;
        publicFis = new FileInputStream(publicKeyFile);
        if (publicFis.read(publicKeyBytes) > 0) {
            X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeyBytes);
            KeyFactory factory = KeyFactory.getInstance("RSA");
            RSAPublicKey pubKey = (RSAPublicKey) factory.generatePublic(publicKeySpec);
            BigInteger pKeyModulus = pubKey.getModulus();
            BigInteger pKeyExponent = pubKey.getPublicExponent();
            System.out.println("PUBLIC KEY EXPO : "+pKeyExponent);

        }

        byte[] privateKeyBytes = new byte[(int) privateKeyFile.length()];
        FileInputStream privateFis = null;
        privateFis = new FileInputStream(privateKeyFile);
        if (privateFis.read(privateKeyBytes) > 0) {
            //PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(privateKeyBytes);
            X509EncodedKeySpec spec = new X509EncodedKeySpec(privateKeyBytes);
            KeyFactory keyFactory = KeyFactory.getInstance("RSA");
            RSAPrivateKey privKey = (RSAPrivateKey) keyFactory.generatePrivate(spec);
            BigInteger pKeyModulus = privKey.getModulus();
            BigInteger pKeyExponent = privKey.getPrivateExponent();
            System.out.println("PRIVATE KEY : "+pKeyExponent);
        } 
    }
}

Please help me whats wrong here ? I assume Private Key should give value something simillar like below":

21150549370950609585296765828149303178265715265804890679831411170495636016527926323370428466362501818569080118374307191403222367256185274427528812911191842330928112748042350818573390540259857225467392220170770506599589136056049534085562156615813126185240565396115577449461468695709719589257257375788267753694280485882595576829517086782992300102288858453543505912425724874212273830247789870669315715724390578125469483751830964757980799543436412647956770560679365767737577100276745456138533646455249170660612983618544127693626739283128573829732806886889896396374650462743743148634276240986662548043510018342217214342529

Answer 1

As per the link :http://codeartisan.blogspot.in/2009/05/public-key-cryptography-in-java.html You should be trying the below

Generate a 2048-bit RSA private key

$ openssl genrsa -out private_key.pem 2048

Convert private Key to PKCS#8 format (so Java can read it)

$ openssl pkcs8 -topk8 -inform PEM -outform DER -in private_key.pem -out private_key.der -nocrypt

Output public key portion in DER format (so Java can read it)

$ openssl rsa -in private_key.pem -pubout -outform DER -out public_key.der

You can read the java code like below:

import java.io.DataInputStream;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.security.KeyFactory;
    import java.security.NoSuchAlgorithmException;
    import java.security.interfaces.RSAPrivateKey;
    import java.security.interfaces.RSAPublicKey;
    import java.security.spec.InvalidKeySpecException;
    import java.security.spec.PKCS8EncodedKeySpec;
    import java.security.spec.X509EncodedKeySpec;

    public class Demo {

        public static final String PRIVATE_KEY="/home/user/private.der";
        public static final String PUBLIC_KEY="/home/user/public.der";

        public static void main(String[] args) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException {
            //get the private key
            File file = new File(PRIVATE_KEY);
            FileInputStream fis = new FileInputStream(file);
            DataInputStream dis = new DataInputStream(fis);

            byte[] keyBytes = new byte[(int) file.length()];
            dis.readFully(keyBytes);
            dis.close();

            PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);
            KeyFactory kf = KeyFactory.getInstance("RSA");
            RSAPrivateKey privKey = (RSAPrivateKey) kf.generatePrivate(spec);
            System.out.println("Exponent :" + privKey.getPrivateExponent());
            System.out.println("Modulus" + privKey.getModulus());

            //get the public key
            File file1 = new File(PUBLIC_KEY);
            FileInputStream fis1 = new FileInputStream(file1);
            DataInputStream dis1 = new DataInputStream(fis1);
            byte[] keyBytes1 = new byte[(int) file1.length()];
            dis1.readFully(keyBytes1);
            dis1.close();

            X509EncodedKeySpec spec1 = new X509EncodedKeySpec(keyBytes1);
            KeyFactory kf1 = KeyFactory.getInstance("RSA");
            RSAPublicKey pubKey = (RSAPublicKey) kf1.generatePublic(spec1);

            System.out.println("Exponent :" + pubKey.getPublicExponent());
            System.out.println("Modulus" + pubKey.getModulus());
        }
    }

Program Output:

PUBLIC KEY EXPO : 65537
PRIVATE KEY : 16540425323481903232154296082061217323015064904150073221896716535825697862890781586244035403066600439504989225032100277459509106847714925918656002207273016950425690931486784061794302602299415224979080443644674838230854689682941689891752703570749249869153966528967635783430367525635094847999700308350727275663213969614628360232440655477057807291869565586695953970804798770095849408924111596670565606097668752646013504502815936286143578191877967720393294592625997337105475883689954727277867955887242546330469781268095607005541678733388864537898085207735975487415418212440417692928205650585590564551063589766600954407329