need to generate RSA keys from txt files

[Bala Raju Mandala]

Hi All,

I want to generate RSA keys from the txt files. I wrote the code by refering Google but it is not much fruitful. Please help me to get the keys from txt files.

getKeys(keySize, output, algorithm);
------------------------------------
Create RSA keys and write them to text files.

encrypt();
----------
read Public key from text file (RSA.pub) and encrypt a file.

decrypt();
----------
read a Private key from text file (RSA.pri) and decrypt the file.


Program i am using to write Keys to files are:

import java.io.*;
import java.math.*;
import java.security.*;
import java.security.interfaces.*;
import java.security.spec.KeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
import javax.crypto.Cipher;

public class JcaKeyPair {
public static void main(String[] a) {
System.out.println("in main");
int keySize = 1024; //1024 bits, 128 bytes
String output = "RSA";
String algorithm = "RSA"; // RSA, DSA
try {
getKeys(keySize, output, algorithm);
//encrypt();
//decrypt();
} catch (Exception e) {
System.out.println("Exception: " + e);
return;
}
}

private static void getKeys(int keySize, String output, String algorithm) throws Exception {
System.out.println("in getKeys method");
KeyPairGenerator kg = KeyPairGenerator.getInstance(algorithm);
kg.initialize(keySize);
System.out.println();
System.out.println("KeyPairGenerator Object Info: ");
System.out.println("Algorithm = " + kg.getAlgorithm());
System.out.println("Provider = " + kg.getProvider());
System.out.println("Key Size = " + keySize);
//System.out.println("toString = " + kg.toString());
KeyPair pair = kg.generateKeyPair();
System.out.println("Key Size = " + keySize);
PrivateKey priKey = pair.getPrivate();
PublicKey pubKey = pair.getPublic();
String fl = output + ".pri";
FileOutputStream out = new FileOutputStream("c:\\encrypt\\" + fl);
byte[] ky = priKey.getEncoded();
out.write(ky);
out.close();
System.out.println();
System.out.println("Private Key Info: ");
System.out.println("Algorithm = " + priKey.getAlgorithm());
System.out.println("Saved File = " + fl);
System.out.println("Size = " + ky.length);
System.out.println("Format = " + priKey.getFormat());
//System.out.println("toString = " + priKey.toString());
fl = output + ".pub";
out = new FileOutputStream("c:\\encrypt\\" + fl);
ky = pubKey.getEncoded();
out.write(ky);
out.close();
System.out.println();
System.out.println("Public Key Info: ");
System.out.println("Algorithm = " + pubKey.getAlgorithm());
System.out.println("Saved File = " + fl);
System.out.println("Size = " + ky.length);
System.out.println("Format = " + pubKey.getFormat());
//System.out.println("toString = " + pubKey.toString());
}

public static void encrypt() {
System.out.println("in Encrypt");
try {
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
String pubKeyFile = "c:\\encrypt\\RSA.pub";
System.out.println("1");
FileInputStream pubKeyStream = new FileInputStream(pubKeyFile);
System.out.println("2");
byte[] pubKeyBytes = new byte[128]; //1024 bits
System.out.println("3");
pubKeyStream.read(pubKeyBytes);
System.out.println("4");
pubKeyStream.close();
System.out.println("5");
X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(pubKeyBytes);
System.out.println("6");
PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);
System.out.println("7");

Cipher cf = Cipher.getInstance("RSA/ECB/NoPadding");
System.out.println("8");
cf.init(Cipher.ENCRYPT_MODE, pubKey);
System.out.println("9");
byte[] data = new byte[128];
byte[] cipher = new byte[128];

FileInputStream fis = new FileInputStream("c:\\encrypt\\Source.txt");
fis.read(data);

cipher = cf.doFinal(data);
System.out.println("3");
FileOutputStream fos = new FileOutputStream("c:\\encrypt\\Data.enc");
fos.write(cipher);
} catch(Exception e) {
System.out.println("Exception in encryption " + e);
}
}

public static void decrypt() {
try {
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
String priKeyFile = "C:\\encrypt\\RSA.pri";
FileInputStream priKeyStream = new FileInputStream(priKeyFile);
byte[] priKeyBytes = new byte[128];
priKeyStream.read(priKeyBytes);
priKeyStream.close();
PKCS8EncodedKeySpec priKeySpec = new PKCS8EncodedKeySpec(priKeyBytes);
PrivateKey priKey = keyFactory.generatePrivate(priKeySpec);

Cipher cf = Cipher.getInstance("RSA/ECB/NoPadding");
cf.init(Cipher.DECRYPT_MODE, priKey);

byte[] cipher = new byte[128];
byte[] plain = new byte[128];

FileInputStream fis = new FileInputStream("C:\\encrypt\\Data.enc");
fis.read(cipher);

plain = cf.doFinal(cipher);

FileOutputStream fos = new FileOutputStream("C:\\encrypt\\Result.txt");
fos.write(plain);
} catch(Exception e) {
System.out.println("Exception in decryption " + e);
}
}
}

It is giving following error message:

Exception in encryption java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: IOException: null

[Ulf Dittmer]

Please edit your post toUseCodeTags. It is unnecessarily hard to read as it is.

In which line of code does the exception occur?

[greg stark]

I have taken the liberty of slightly rewriting the code so that I could eliminate the hard-coded absolute pathnames, and I'll post that here with code tags. I'll comment on the bugs in the next reply.

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
 
import javax.crypto.Cipher;
 
public class JcaKeyPair
{
    private final File privKeyFile;
 
    private final File pubKeyFile;
 
    public JcaKeyPair(int keySize, String output, String algorithm) throws Exception
    {
        this.privKeyFile = new File(output + ".pri");
        this.pubKeyFile = new File(output + ".pub");
        System.out.println("in JcaKeyPair constructor");
        KeyPairGenerator kg = KeyPairGenerator.getInstance(algorithm);
        kg.initialize(keySize);
        System.out.println();
        System.out.println("KeyPairGenerator Object Info: ");
        System.out.println("Algorithm = " + kg.getAlgorithm());
        System.out.println("Provider = " + kg.getProvider());
        System.out.println("Key Size = " + keySize);
        // System.out.println("toString = " + kg.toString());
        KeyPair pair = kg.generateKeyPair();
        System.out.println("Key Size = " + keySize);
        PrivateKey priKey = pair.getPrivate();
        PublicKey pubKey = pair.getPublic();
        FileOutputStream out = new FileOutputStream(privKeyFile);
        byte[] ky = priKey.getEncoded();
        out.write(ky);
        out.close();
        System.out.println();
        System.out.println("Private Key Info: ");
        System.out.println("Algorithm = " + priKey.getAlgorithm());
        System.out.println("Saved File = " + privKeyFile.getCanonicalPath());
        System.out.println("Size = " + ky.length);
        System.out.println("Format = " + priKey.getFormat());
        // System.out.println("toString = " + priKey.toString());
        out = new FileOutputStream(pubKeyFile);
        ky = pubKey.getEncoded();
        out.write(ky);
        out.close();
        System.out.println();
        System.out.println("Public Key Info: ");
        System.out.println("Algorithm = " + pubKey.getAlgorithm());
        System.out.println("Saved File = " + pubKeyFile.getCanonicalPath());
        System.out.println("Size = " + ky.length);
        System.out.println("Format = " + pubKey.getFormat());
        // System.out.println("toString = " + pubKey.toString());
    }
 
    public void encrypt() throws Exception
    {
        System.out.println("in Encrypt");
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        System.out.println("1");
        FileInputStream pubKeyStream = new FileInputStream(pubKeyFile);
        System.out.println("2");
        byte[] pubKeyBytes = new byte[128]; // 1024 bits
        System.out.println("3");
        pubKeyStream.read(pubKeyBytes);
        System.out.println("4");
        pubKeyStream.close();
        System.out.println("5");
        X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(pubKeyBytes);
        System.out.println("6");
        PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);
        System.out.println("7");
 
        Cipher cf = Cipher.getInstance("RSA/ECB/NoPadding");
        System.out.println("8");
        cf.init(Cipher.ENCRYPT_MODE, pubKey);
        System.out.println("9");
        byte[] data = new byte[128];
        byte[] cipher = new byte[128];
 
        FileInputStream fis = new FileInputStream("Source.txt");
        fis.read(data);
 
        cipher = cf.doFinal(data);
        System.out.println("3");
        FileOutputStream fos = new FileOutputStream("Data.enc");
        fos.write(cipher);
    }
 
    public void decrypt() throws Exception
    {
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        FileInputStream priKeyStream = new FileInputStream(privKeyFile);
        byte[] priKeyBytes = new byte[128];
        priKeyStream.read(priKeyBytes);
        priKeyStream.close();
        PKCS8EncodedKeySpec priKeySpec = new PKCS8EncodedKeySpec(priKeyBytes);
        PrivateKey priKey = keyFactory.generatePrivate(priKeySpec);
 
        Cipher cf = Cipher.getInstance("RSA/ECB/NoPadding");
        cf.init(Cipher.DECRYPT_MODE, priKey);
 
        byte[] cipher = new byte[128];
        byte[] plain = new byte[128];
 
        FileInputStream fis = new FileInputStream("Data.enc");
        fis.read(cipher);
 
        plain = cf.doFinal(cipher);
 
        FileOutputStream fos = new FileOutputStream("Result.txt");
        fos.write(plain);
    }
    
    public static void main(String[] a) throws Exception
    {
        System.out.println("in main");
        int keySize = 1024; // 1024 bits, 128 bytes
        String output = "RSA";
        String algorithm = "RSA"; // RSA, DSA
        JcaKeyPair jcaKeyPair = new JcaKeyPair(keySize, output, algorithm);
        jcaKeyPair.encrypt();
        jcaKeyPair.decrypt();
    }
}

[greg stark]

Your first mistake occurs in

        byte[] pubKeyBytes = new byte[128]; // 1024 bits
        System.out.println("3");
        pubKeyStream.read(pubKeyBytes);
        System.out.println("4");
        pubKeyStream.close();
    

Note that, while the modulus may be 1024 bits, the public key consists of at least the modulus and the exponent. In fact, it contains even more information, such as the fact the public key algorithm is RSA, and other descriptive information. On my computer, in the one instance I checked, this file was in fact 162 bytes in length. Never assume you know what the length is in advance. Either save the length somewhere (ky.length), or let the filesystem tell you the length. You should become familiar with the DataInputStream and DataOutputStream classes; they are very useful. For example, consider this alternative sequence of Java which produces the correct result:

        DataInputStream pubKeyStream = new DataInputStream(new FileInputStream(pubKeyFile));
        System.out.println("2");
//      byte[] pubKeyBytes = new byte[128]; // 1024 bits
        byte[] pubKeyBytes = new byte[(int) pubKeyFile.length()]; // 1024 bits
        System.out.println("3");
//        pubKeyStream.read(pubKeyBytes);
        pubKeyStream.readFully(pubKeyBytes);
        System.out.println("4");
        pubKeyStream.close();
    

I have not examined the rest of the code for errors.

[Bala Raju Mandala]

Thank you Ulf and Greg. But these changes are not made any difference, i am getting same exception. I am searching google for references, but they are using MD5 to encode and checking signatures also. I am confused can't we simply read from txt files and recreate the RSA keys? is it is not that simpler? folks please help!
[ September 21, 2008: Message edited by: Bala Raju Mandala ]

[greg stark]

I am confused can't we simply read from txt files and recreate the RSA keys?

I can, using the code fragment I provided.

[Bala Raju Mandala]

Yes, i did some mistakes. Your code is working. Thank you once again.

[sergio martinelli]

I suggest you use the API Bouncy Castle OpenPGP are easy to use and well documented.