Write public/private key to the SharedPreferences and use it

Question

I am trying to encrypt and decrypt a text with public/private keys.First of all, I create my keys and store them in sharedpreferences with this code :

SharedPreferences SP;

SharedPreferences.Editor SPE;

KeyPairGenerator keyGen;

KeyPair keypair;

PublicKey publicKey;

PrivateKey privateKey;

keyGen = KeyPairGenerator.getInstance("RSA"); 

keyGen.initialize(1024);        

keypair = keyGen.genKeyPair();

privateKey = keypair.getPrivate(); 

publicKey = keypair.getPublic();

SPE = SP.edit();

SPE.putString("PublicKey", publicKey.toString());

SPE.putString("PrivateKey", privateKey.toString());

SPE.commit();

In my SharedPreferences file, keys are written like this :

PublicKey: RSA Public Key

modulus: d07b8f32968cf65301fd710f9d6d036feac01d7b98c92ff979cd324d252cb257ff48d6630b33f0f68bd0ee81c3a83502a0abf0b263dc96c2b86940f7ec19ab1865626383e55cf5a37e25ef4eb6ca88a39f31becb6065434bc2236177aa5b35266fe0379164faea6ef7a92812e7aa3ef5fc488c70ab085f5564f09c0f6e927b49

public exponent: 10001

PrivateKey: RSA Private CRT Key

modulus: d07b8f32968cf65301fd710f9d6d036feac01d7b98c92ff979cd324d252cb257ff48d6630b33f0f68bd0ee81c3a83502a0abf0b263dc96c2b86940f7ec19ab1865626383e55cf5a37e25ef4eb6ca88a39f31becb6065434bc2236177aa5b35266fe0379164faea6ef7a92812e7aa3ef5fc488c70ab085f5564f09c0f6e927b49

public exponent: 10001
private exponent: 67ebef696c1a3fff0892e8f4bba8477a562e05844298a6cd58a5ac59401a939bc1a8f114d5d4c25c633d766640bd6c0f2f4005ef265022e6553e4220531448702e4bbf4322b9d5cf444d16eea151e5d565412b49208a73d9236607475d201affa21d374e3186f14b651b08565be4725f89fc6797a79c8433c4dd089589284a01

primeP: ee4ad1a56f4ee3b12c198d09b08a92c349f94cc79a6143ca7140fa64c919f2d9c24c29d3b413fdc4039000b6b5feac5a764ce436db4a4a382d8ceecbc768e0d1

primeQ: dff9a761807440b4a5a4fb04ebaa22849f6543f33168bd6e83b3c549b346661124d7879e168c1009e97c01b3fdcd7088eebd9c989b64d7c4b81ea46f9e06d0f9

primeExponentP: 2ce01e371f8d25c819dbfdf9932ba593ed7c6b7f338d99aca8436a644c92fc6f11ee31fa5271695adea8e1d986d09d38b40aaaf7c1b86dddc28645fa4e656be1

primeExponentQ: 21904af9fc82ef5362e3474ea4763978005eef80d92da5fd92b4f4e2a77fec39b378acf50ed1ec715fd0da7c7b9336c2fe6be1b4a8ccc2dcd2ee9c9bb165ba19

crtCoefficient: d8ccccb874ec4c2d464e84829547507e1ebf78e506caa77950b04329957b8713e80553874b825bf5c90b214984b4657b64965867460d87aab135f43930db48ec

And with this code i am trying to read this keys :

private PublicKey getPublicKey() throws UnsupportedEncodingException, NoSuchAlgorithmException, InvalidKeySpecException{

    byte[] keyBytes = Base64.decodeBase64(SP.getString("PublicKey", "default value").getBytes("utf-8"));
    X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    PublicKey key = keyFactory.generatePublic(spec);
    return key;}

But something goes wrong.It gives InvalidKeySpecException. I thing this cannot read the keys from file.How can i fix this problem? Thank you.

Answer 1

Ok. I found some solution and change something. This is new class for public/private key storing and getting it again from stored string. This class works for me !

import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;
import org.bouncycastle.util.encoders.Base64;
import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;

public class KeyGenerator extends Activity{

    SharedPreferences SP;
    SharedPreferences.Editor SPE;
    PublicKey pubKey;
    PrivateKey privKey; 
    Context context;

    public KeyGenerator(Context context){
        this.context = context;
        SP = context.getSharedPreferences("KeyPair", MODE_PRIVATE);
    }

    public void generateKeys(){
        try {
            KeyPairGenerator generator;
            generator = KeyPairGenerator.getInstance("RSA", "BC");
            generator.initialize(256, new SecureRandom());
            KeyPair pair = generator.generateKeyPair();
            pubKey = pair.getPublic();
            privKey = pair.getPrivate();            
            byte[] publicKeyBytes = pubKey.getEncoded();
            String pubKeyStr = new String(Base64.encode(publicKeyBytes));
            byte[] privKeyBytes = privKey.getEncoded();
            String privKeyStr = new String(Base64.encode(privKeyBytes));            
            SPE = SP.edit();
            SPE.putString("PublicKey", pubKeyStr);
            SPE.putString("PrivateKey", privKeyStr);           
            SPE.commit();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        }           
    }
    public PublicKey getPublicKey(){
        String pubKeyStr = SP.getString("PublicKey", "");       
        byte[] sigBytes = Base64.decode(pubKeyStr);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(sigBytes);
        KeyFactory keyFact = null;
        try {
            keyFact = KeyFactory.getInstance("RSA", "BC");
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        }
        try {
            return  keyFact.generatePublic(x509KeySpec);
        } catch (InvalidKeySpecException e) {
            e.printStackTrace();
        }
        return null;
    }
    public String getPublicKeyAsString(){
        return SP.getString("PublicKey", "");       
    }
    public PrivateKey getPrivateKey(){
        String privKeyStr = SP.getString("PrivateKey", "");
        byte[] sigBytes = Base64.decode(privKeyStr);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(sigBytes);
        KeyFactory keyFact = null;
        try {
            keyFact = KeyFactory.getInstance("RSA", "BC");
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        }
        try {
            return  keyFact.generatePrivate(x509KeySpec);
        } catch (InvalidKeySpecException e) {
            e.printStackTrace();
        }
        return null;
    }
    public String getPrivateKeyAsString(){
        return SP.getString("PrivateKey", "");      
    }
}

Answer 2

Thanks for the accepted code above (maybe below). However, in my case, the 'getPrivatekey()' throws an InvalidKeySpecException. It says 'Unknown KeySpc type: java.secrity.spec.X509EncodedKeySpec'. The solution I used is to replace X509EncodedKeySpec with PKCS8EncodedKeySpec. Then it works! Reference: https://stackoverflow.com/a/9755391/2481444