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problem while decrypting private key getting javax.crypto.AEADBadTagException: Tag mismatch! Error

I have been trying to figure this out for 2 days now. Encryption method works fine, but during the decryption tests I am getting the exception below. Especially I am using: AES/GCM/NoPadding.
Error :
Exception in thread "main" javax.crypto.AEADBadTagException: Tag mismatch!
at java.base/com.sun.crypto.provider.GaloisCounterMode.decryptFinal(GaloisCounterMode.java:623)
at java.base/com.sun.crypto.provider.CipherCore.finalNoPadding(CipherCore.java:1116)
at java.base/com.sun.crypto.provider.CipherCore.fillOutputBuffer(CipherCore.java:1053)
at java.base/com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:853)
at java.base/com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:446)
at java.base/javax.crypto.Cipher.doFinal(Cipher.java:2202)
at com.solarwinds.whd.symmetric.GSMTest.decrypt(GSMTest.java:72)
at com.solarwinds.whd.symmetric.GSMTest.main(GSMTest.java:38)
Code:
import javax.crypto.*;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.UnsupportedEncodingException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import static java.nio.charset.StandardCharsets.UTF_8;
public class GSMTest {
private static final String ALGORITHM = "AES";
private static final int T_LEN = 128;
private static final int IV_LENGTH = 12;
public static void main(String[] args) throws NoSuchAlgorithmException, InvalidAlgorithmParameterException, UnsupportedEncodingException, InvalidKeyException, IllegalBlockSizeException, NoSuchPaddingException, BadPaddingException {
String s = "xaT2UtvzIt2rO8OMxaT2UtvzIt2rO8OM";
KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
keyGenerator.init(256);
SecretKey key = keyGenerator.generateKey();
GSMTest ob = new GSMTest();
System.out.println("Before encrypt: "+s);
String se = ob.encrypt(s, key);
System.out.println("After encrypt: "+se);
String sd = ob.decrypt(se, key);
System.out.println("After decrypt: "+sd);
}
public String encrypt(String text, SecretKey key) throws UnsupportedEncodingException, IllegalBlockSizeException, BadPaddingException, NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, NoSuchPaddingException, IllegalBlockSizeException {
byte[] iv = new byte[IV_LENGTH];
(new SecureRandom()).nextBytes(iv);
SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(), ALGORITHM);
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
GCMParameterSpec ivSpec = new GCMParameterSpec(T_LEN, iv);
cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
byte[] ciphertext = cipher.doFinal(text.getBytes(UTF_8));
byte[] encrypted = new byte[iv.length + ciphertext.length];
System.arraycopy(iv, 0, encrypted, 0, iv.length);
System.arraycopy(ciphertext, 0, encrypted, iv.length, ciphertext.length);
Base64.Encoder en = Base64.getEncoder();
return en.encodeToString(encrypted);
}
public String decrypt(String encryptedText, SecretKey key) throws IllegalBlockSizeException, BadPaddingException, NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException {
Base64.Decoder de = Base64.getDecoder();
byte[] decoded = de.decode(encryptedText);
byte[] iv = Arrays.copyOfRange(decoded, IV_LENGTH, decoded.length);
SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(), ALGORITHM);
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
GCMParameterSpec ivSpec = new GCMParameterSpec(T_LEN, iv);
cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
byte[] decryptedText = cipher.doFinal(decoded);
return new String(decryptedText);
}
}
Can anyone help? I have been reading many about, and still cannot find anything wrong.

Hybrid RSA-AES encryption

i try to create hybrid encryption using RSA-AES but for now i face a problem in this coding. From this code i try to Creating an RSA key pair , private and public key. After that i should Generating a random key symmetrical algorithm AES then i have to create an AES cipher in order to encrypt a text string with the AES key. Then after the text is encrypted with the AES key, then the AES key needs to be encrypted with the RSA public key and the encrypted AES key needs to be decrypted with the RSA private key. And finally decrypt the text message entered with AES key in order to read the message. I think i missing something in my coding. Please help me guys.
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
import java.security.spec.EncodedKeySpec;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;
public class HybridAesRsa
{
private Cipher cipher;
// RSA keys will be generated when the client and server connect
private PrivateKey myPrivateKey;
private byte[] myPublicKey;
private byte[] interlocutorPublicKey = null;
// Strings are encoded / decoded in BASE64
private BASE64Decoder b64decoder = new BASE64Decoder();
private BASE64Encoder b64encoder = new BASE64Encoder();
public HybridAesRsa()
{
try
{
cipher = Cipher.getInstance("RSA");
Security.addProvider(new BouncyCastleProvider());
}
catch (Exception ex){
Logger.getLogger(HybridAesRsa.class.getName()).log(Level.SEVERE,null,ex);
}
}
// Generate the pair of public and private keys using 1024 bytes
public KeyPair generateKey() throws Exception
{
KeyPair keyPair = null;
try{
//generate RSA key pair
KeyPairGenerator rsaKeyGen = KeyPairGenerator.getInstance("RSA");
rsaKeyGen.initialize(1024);
keyPair = rsaKeyGen.generateKeyPair();
//RSA public and private key
PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();
//System.out.println("RSA public key 1 ---> "+publicKey);
//System.out.println("RSA private key 1 ---> " +privateKey);
//for Chatting
myPublicKey = publicKey.getEncoded();
setMyPrivateKey(privateKey);
//Generating a random key symmetrical algorithm AES
KeyGenerator aesKeyGenerator = KeyGenerator.getInstance("AES");
SecureRandom random = new SecureRandom();
aesKeyGenerator.init(random);
SecretKey aesSecretKey = aesKeyGenerator.generateKey();
/*//The key is presented in a byte array
byte[] symmetricKey = aesSecretKey.getEncoded();
//Printing out the generated key
System.out.println("\nAES symmetric key --> " + symmetricKey); */
} catch (NoSuchAlgorithmException ex) {
Logger.getLogger(HybridAesRsa.class.getName()).log(Level.SEVERE,null,ex);
}
return keyPair;
}
// Encrypts text using public key
public String encrypt(String text, PublicKey publicKey, SecretKey aesSecretKey ) throws Exception
{
//Creating an AES cipher in order to encrypt a text string with the AES key
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, aesSecretKey);
//Now that the text is encrypted with the AES key, then the AES key needs to be encrypted with the RSA public key
Cipher rsaCipher = Cipher.getInstance("RSA");
rsaCipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] encryptedAESkey = rsaCipher.doFinal(aesSecretKey.getEncoded());
//Printing out the encrypted AES key
System.out.println("\nAES key encrypted with RSA --> " + encryptedAESkey);
return text;
}
// Use the public key to encrypt the interlocutor
public String encrypt(String text) throws Exception
{
return encrypt(text, bytesToPublicKey(interlocutorPublicKey), null);
}
// Decrypts text using private key
public String decrypt(String text, PrivateKey privatekey) throws Exception
{
// Now the encrypted AES key needs to be decrypted with the RSA private key
Cipher rsaCipher2 = Cipher.getInstance("RSA");
rsaCipher2.init(Cipher.DECRYPT_MODE, privatekey);
byte[] encryptedAESkey = null;
byte[] decryptedAESkey = rsaCipher2.doFinal(encryptedAESkey);
//Print out the decrypted AES key
System.out.println("AES key decrypted with RSA private key --> " + decryptedAESkey);
//And finally decrypt the text message entered with AES key in order to read the message.
Cipher aesCipher2 = Cipher.getInstance("AES");
Key aesSecretKey = null;
aesCipher2.init(Cipher.DECRYPT_MODE,aesSecretKey);
byte[] encrypt = null;
byte [] decrypt = aesCipher2.doFinal(encrypt);
return text;
}
// Use my private key to decrypt
public String decrypt(String text) throws Exception
{
return decrypt(text, myPrivateKey);
}
// Public Key the caller is sent in byte [ ] and converted into a PublicKey object
public static PublicKey bytesToPublicKey(byte[] publicKeybytes)
{
PublicKey publicKey = null;
try {
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKeybytes);
publicKey = keyFactory.generatePublic(publicKeySpec);
}
catch (InvalidKeySpecException ex) {
Logger.getLogger(HybridAesRsa.class.getName()).log(Level.SEVERE, null, ex);
}
catch (NoSuchAlgorithmException ex){
Logger.getLogger(HybridAesRsa.class.getName()).log(Level.SEVERE, null, ex);
}
return publicKey;
}
// Test
public static void main(String[] args){
try {
HybridAesRsa crypto = new HybridAesRsa();
KeyPair keyPair = crypto.generateKey();
PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();
KeyGenerator aesKeyGenerator = KeyGenerator.getInstance("AES");
SecretKey aesSecretKey = aesKeyGenerator.generateKey();
byte[] publicKeyBytes = publicKey.getEncoded();
byte[] privateKeyBytes = privateKey.getEncoded();
byte[] symmetricKey = aesSecretKey.getEncoded();
System.out.println("RSA Public key: " + new BigInteger(publicKeyBytes));
System.out.println("RSA Private key: " + new BigInteger(privateKeyBytes));
System.out.println("AES symmetric key --> " + new BigInteger(symmetricKey));
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, aesSecretKey);
String testeMsg = "As a seed knows how to make a flower ? I love you.";
byte[] encrypt = aesCipher.doFinal(testeMsg.getBytes());
Cipher rsaCipher = Cipher.getInstance("RSA");
rsaCipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] encryptedAESkey = rsaCipher.doFinal(aesSecretKey.getEncoded());
String encrypted = crypto.encrypt(testeMsg, bytesToPublicKey(publicKeyBytes), aesSecretKey);
System.out.println("Encrypted Text: " + encrypted);
String decrypted = crypto.decrypt(encrypted, keyPair.getPrivate());
System.out.println("Decrypted Text: " + decrypted);
}
catch (Exception ex)
{
Logger.getLogger(HybridAesRsa.class.getName()).log(Level.SEVERE, null, ex);
}
}
public byte[] getMyPublicKey(){
return myPublicKey;
}
public void setMyPublicKey(byte[] myPublicKey) {
this.myPublicKey = myPublicKey;
}
public PrivateKey getMyPrivateKey(){
return myPrivateKey;
}
public byte[] getInterlocutorPublicKey(){
return interlocutorPublicKey;
}
public boolean hasInterlocutorPublicKey(){
return interlocutorPublicKey!=null;
}
public void setInterlocutorPublicKey(byte[] interlocutorPublicKey){
this.interlocutorPublicKey = interlocutorPublicKey;
}
public void setMyPrivateKey(PrivateKey aMyPrivateKey){
myPrivateKey = aMyPrivateKey;
}
}
Here the error for this code
Jun 19, 2016 5:50:14 PM HybridAesRsa main
SEVERE: null
java.lang.IllegalArgumentException: Null input buffer
at javax.crypto.Cipher.doFinal(Cipher.java:2117)
at HybridAesRsa.decrypt(HybridAesRsa.java:125)
at HybridAesRsa.main(HybridAesRsa.java:204)

You have this code:
byte[] encrypt = null;
byte [] decrypt = aesCipher2.doFinal(encrypt);
where you try to encrypt with a buffer that's initialised to null .. that is not possible.
The exception is quite clear:
java.lang.IllegalArgumentException: Null input buffer

How to implement password based hybrid encryption in java?

I'm currently working on an Android project for developing a Hybrid File Encryption. From this site, I've already created a hybrid encryption which only able to encrypt text/string. While all the keys are automatically generated within the code. Any idea on how to make the keys to be user input password based and able to encrypt files?
Here is the code:
// Some codes here
// Create key pair (public and private key) for RSA encryption and decryption
try {
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
kp = kpg.genKeyPair();
publicKey = kp.getPublic();
privateKey = kp.getPrivate();
} catch (Exception e) {
Log.e(TAG, "RSA key pair error");
}
}
private void encHybrid() throws GeneralSecurityException {
// Create random secret key with AES algorithm
KeyGenerator kg = KeyGenerator.getInstance("AES");
kg.init(128, sr) ;
SecretKey cipherKey = kg.generateKey() ;
// Encrypt secret key asymmetry algorithm (RSA)
encryptedSecretKey = encrypt(cipherKey.getEncoded(), kp.getPublic());
textHybrid = etHybrid.getText().toString();
// Encrypt inputted text/string with symmetry algorithm using encrypted secret key
encryptedData = encrypt(textHybrid.getBytes(), cipherKey);
}
// Method to encrypt the text/string
public static byte[] encrypt(byte[] toEncrypt, SecretKey key)
throws GeneralSecurityException {
Cipher cipher = Cipher.getInstance("AES") ;
cipher.init(Cipher.ENCRYPT_MODE, key) ;
return cipher.doFinal(toEncrypt);
}
// Method to encrypt the secret key
public static byte[] encrypt(byte[] toEncrypt, PublicKey key)
throws GeneralSecurityException {
Cipher cipher = Cipher.getInstance("RSA") ;
cipher.init(Cipher.ENCRYPT_MODE, key) ;
return cipher.doFinal(toEncrypt);
}
private void decryptHybrid() throws GeneralSecurityException {
// Decrypt secret key with private key
byte[] decryptedSecretKey = decrypt(encryptedSecretKey, kp.getPrivate()) ;
// Decrypted secret key will be stored in sKey
SecretKey sKey = new SecretKeySpec(decryptedSecretKey, "AES") ;
textHybrid = etHybrid.getText().toString();
// Decrypt encrypted text/string with decrypted secret key
byte[] decryptedData = decrypt(encryptedData, sKey) ;
}
// Method to decrypt the text/string
public static byte[] decrypt(byte[] toDecrypt, SecretKey key)
throws GeneralSecurityException {
Cipher deCipher = Cipher.getInstance("AES") ;
deCipher.init(Cipher.DECRYPT_MODE, key) ;
return deCipher.doFinal(toDecrypt);
}
// Method to decrypt the secret key
public static byte[] decrypt(byte[] toDecrypt, PrivateKey key)
throws GeneralSecurityException {
Cipher deCipher = Cipher.getInstance("RSA") ;
deCipher.init(Cipher.DECRYPT_MODE, key) ;
return deCipher.doFinal(toDecrypt);
}

You don't really want to generate the key pair from the password. The problem with that scheme is that there is no way to trust the public key. What is usually done is to encrypt the private key with a secret (symmetric) key that has been generated from a password.
So, in addition to the hybrid encryption you would have a scheme that does it entirely the other way around. It's a bit of code, but it should be readable enough. Or you could use PGP, which essentially performs the same kind of operations.
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.KeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
public class PassphraseWrapRSA {
private static KeyPair generateRSAKeyPair(final int size) {
KeyPairGenerator kpgen;
try {
kpgen = KeyPairGenerator.getInstance("RSA");
} catch (final NoSuchAlgorithmException e) {
throw new IllegalStateException();
}
kpgen.initialize(size);
return kpgen.generateKeyPair();
}
public static byte[] generateSalt() {
final SecureRandom rng = new SecureRandom();
final byte[] salt = new byte[16];
rng.nextBytes(salt);
return salt;
}
private static SecretKey deriveAESKey(final byte[] salt,
final char[] password) {
try {
final SecretKeyFactory factory = SecretKeyFactory
.getInstance("PBKDF2WithHmacSHA1");
final KeySpec spec = new PBEKeySpec(password, salt, 65536, 256);
final SecretKey keyWrapKey = factory.generateSecret(spec);
final SecretKey secret = new SecretKeySpec(keyWrapKey.getEncoded(),
"AES");
return secret;
} catch (final Exception e) {
throw new IllegalStateException(e);
}
}
private static byte[] encryptRSAPrivateKey(final RSAPrivateKey rsaPrivateKey,
final SecretKey aesKey) {
try {
final Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
final SecureRandom ivGen = new SecureRandom();
final byte[] iv = new byte[c.getBlockSize()];
ivGen.nextBytes(iv);
c.init(Cipher.WRAP_MODE, aesKey, new IvParameterSpec(iv));
final byte[] wrappedKey = c.wrap(rsaPrivateKey);
return concat(iv, wrappedKey);
} catch (final GeneralSecurityException e) {
throw new IllegalStateException(e);
}
}
public static byte[] wrapRSAPrivateKey(final String passphrase,
final RSAPrivateKey rsaPrivateKey) {
// --- generate salt
final byte[] newSalt = generateSalt();
// --- derive symmetric key from salt and password
final SecretKey aesKey = deriveAESKey(newSalt,
passphrase.toCharArray());
final byte[] encryptedPrivate = encryptRSAPrivateKey(rsaPrivateKey, aesKey);
final byte[] saltedAndEncryptedPrivate = concat(newSalt,
encryptedPrivate);
return saltedAndEncryptedPrivate;
}
private static RSAPrivateKey decryptRSAPrivateKey(final byte[] encryptedRSAPrivateKey,
final SecretKey aesKey) throws InvalidKeyException {
try {
final Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
int offset = 0;
final byte[] iv = Arrays.copyOfRange(encryptedRSAPrivateKey, 0,
c.getBlockSize());
offset += c.getBlockSize();
c.init(Cipher.UNWRAP_MODE, aesKey, new IvParameterSpec(iv));
final Key key = c.unwrap(Arrays.copyOfRange(encryptedRSAPrivateKey, offset,
encryptedRSAPrivateKey.length), "RSA", Cipher.PRIVATE_KEY);
return (RSAPrivateKey) key;
} catch (final InvalidKeyException e) {
throw e;
} catch (final GeneralSecurityException e) {
throw new IllegalStateException(e);
}
}
public static RSAPrivateKey unwrapRSAPrivateKey(final String passphrase,
final byte[] saltedAndEncryptedPrivate) throws InvalidKeyException {
int offset = 0;
final byte[] backSalt = Arrays.copyOfRange(saltedAndEncryptedPrivate,
offset, 16);
offset += 16;
final SecretKey backAESKey = deriveAESKey(backSalt,
passphrase.toCharArray());
final byte[] backEncryptedPrivateKey = Arrays.copyOfRange(
saltedAndEncryptedPrivate, offset,
saltedAndEncryptedPrivate.length);
final RSAPrivateKey decryptedPrivate = decryptRSAPrivateKey(
backEncryptedPrivateKey, backAESKey);
return decryptedPrivate;
}
public static RSAPublicKey decodeRSAPublicKey(
final byte[] x509EncodedPUblicKey) throws InvalidKeySpecException {
try {
final KeyFactory rsaPublicKeyFactory = KeyFactory.getInstance("RSA");
final PublicKey pubKey = rsaPublicKeyFactory
.generatePublic(new X509EncodedKeySpec(x509EncodedPUblicKey));
return (RSAPublicKey) pubKey;
} catch (final InvalidKeySpecException e) {
throw e;
} catch (final GeneralSecurityException e) {
throw new IllegalStateException(e);
}
}
public static byte[] encodeRSAPublicKey(final RSAPublicKey rsaPublicKey) {
return rsaPublicKey.getEncoded();
}
private static byte[] concat(final byte[] a, final byte[] a2) {
final byte[] result = new byte[a.length + a2.length];
System.arraycopy(a, 0, result, 0, a.length);
System.arraycopy(a2, 0, result, a.length, a2.length);
return result;
}
public static void main(final String[] args) throws Exception {
// --- not required for Java 8
Security.addProvider(new BouncyCastleProvider());
// --- setup key pair (generated in advance)
final String passphrase = "owlstead";
final KeyPair kp = generateRSAKeyPair(1024);
final RSAPublicKey rsaPublicKey = (RSAPublicKey) kp.getPublic();
final RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) kp.getPrivate();
// --- encode and wrap
byte[] x509EncodedRSAPublicKey = encodeRSAPublicKey(rsaPublicKey);
final byte[] saltedAndEncryptedPrivate = wrapRSAPrivateKey(
passphrase, rsaPrivateKey);
// --- decode and unwrap
final RSAPublicKey retrievedRSAPublicKey = decodeRSAPublicKey(x509EncodedRSAPublicKey);
final RSAPrivateKey retrievedRSAPrivateKey = unwrapRSAPrivateKey(passphrase,
saltedAndEncryptedPrivate);
// --- check result
System.out.println(retrievedRSAPublicKey);
System.out.println(retrievedRSAPrivateKey);
}
}
WARNING: for demonstration purposes only, please implement using classes and a more flexible method of handling the protocol (include e.g. a version number) etc.

RSA implementation using java

I am implementing RSA in java I have encountered a code which is given below it is showing plaintext in numeric form after decrypting the plaintext, but I want it in simple english which I entered. I don't want to use the java api.
TestRsa.Java
import java.io.IOException;
import java.math.BigInteger;
import java.util.Random;
public class TestRsa {
private BigInteger p, q;
private BigInteger n;
private BigInteger PhiN;
private BigInteger e, d;
public TestRsa() {
initialize();
}
public void initialize() {
int SIZE = 512;
/* Step 1: Select two large prime numbers. Say p and q. */
p = new BigInteger(SIZE, 15, new Random());
q = new BigInteger(SIZE, 15, new Random());
/* Step 2: Calculate n = p.q */
n = p.multiply(q);
/* Step 3: Calculate ø(n) = (p - 1).(q - 1) */
PhiN = p.subtract(BigInteger.valueOf(1));
PhiN = PhiN.multiply(q.subtract(BigInteger.valueOf(1)));
/* Step 4: Find e such that gcd(e, ø(n)) = 1 ; 1 < e < ø(n) */
do {
e = new BigInteger(2 * SIZE, new Random());
} while ((e.compareTo(PhiN) != 1)
|| (e.gcd(PhiN).compareTo(BigInteger.valueOf(1)) != 0));
/* Step 5: Calculate d such that e.d = 1 (mod ø(n)) */
d = e.modInverse(PhiN);
}
public BigInteger encrypt(BigInteger plaintext) {
return plaintext.modPow(e, n);
}
public BigInteger decrypt(BigInteger ciphertext) {
return ciphertext.modPow(d, n);
}
public static void main(String[] args) throws IOException {
TestRsa app = new TestRsa();
int plaintext;
System.out.println("Enter any character : ");
plaintext = System.in.read();
BigInteger bplaintext, bciphertext;
bplaintext = BigInteger.valueOf((long) plaintext);
bciphertext = app.encrypt(bplaintext);
System.out.println("Plaintext : " + bplaintext.toString());
System.out.println("Ciphertext : " + bciphertext.toString());
bplaintext = app.decrypt(bciphertext);
System.out.println("After Decryption Plaintext : "
+ bplaintext.toString());
}
}

My RSA Class:
package com.infovale.cripto;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Arrays;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
public class RSA {
static String kPublic = "";
static String kPrivate = "";
public RSA()
{
}
public String Encrypt(String plain) throws NoSuchAlgorithmException,
NoSuchPaddingException, InvalidKeyException,
IllegalBlockSizeException, BadPaddingException {
String encrypted;
byte[] encryptedBytes;
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
KeyPair kp = kpg.genKeyPair();
PublicKey publicKey = kp.getPublic();
PrivateKey privateKey = kp.getPrivate();
byte[] publicKeyBytes = publicKey.getEncoded();
byte[] privateKeyBytes = privateKey.getEncoded();
kPublic = bytesToString(publicKeyBytes);
kPrivate = bytesToString(privateKeyBytes);
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
encryptedBytes = cipher.doFinal(plain.getBytes());
encrypted = bytesToString(encryptedBytes);
return encrypted;
}
public String Decrypt(String result) throws NoSuchAlgorithmException,
NoSuchPaddingException, InvalidKeyException,
IllegalBlockSizeException, BadPaddingException {
byte[] decryptedBytes;
byte[] byteKeyPrivate = stringToBytes(kPrivate);
KeyFactory kf = KeyFactory.getInstance("RSA");
PrivateKey privateKey = null;
try {
privateKey = kf.generatePrivate(new PKCS8EncodedKeySpec(byteKeyPrivate));
} catch (InvalidKeySpecException e) {
e.printStackTrace();
}
String decrypted;
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
decryptedBytes = cipher.doFinal(stringToBytes(result));
decrypted = new String(decryptedBytes);
return decrypted;
}
public String bytesToString(byte[] b) {
byte[] b2 = new byte[b.length + 1];
b2[0] = 1;
System.arraycopy(b, 0, b2, 1, b.length);
return new BigInteger(b2).toString(36);
}
public byte[] stringToBytes(String s) {
byte[] b2 = new BigInteger(s, 36).toByteArray();
return Arrays.copyOfRange(b2, 1, b2.length);
}
}

try these lines:
System.out.println("Plaintext : " + new String(bplaintext.toByteArray() ) );
System.out.println("Ciphertext : " + new String(bciphertext.toByteArray() ) );
bplaintext = app.decrypt(bciphertext);
System.out.println("After Decryption Plaintext : " + new String(bplaintext.toByteArray() ) );

I edited Elton Da Costa's class a little bit adding that feature to convert Public key from String to PublicKey class. Because the user of this class might ultimately want to give out the public key to a third party for encryption of the message and keep the private key with himself for decryption.
package com.custom.util;
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
public class RSA {
static String kPublic = "";
static String kPrivate = "";
public RSA() {
}
public class KeyPairStrings {
private String pubKey;
private String privKey;
public String getPubKey() {
return pubKey;
}
public String getPrivKey() {
return privKey;
}
#Override
public String toString() {
return "KeyPairStrings [pubKey=" + pubKey + ", privKey=" + privKey + "]";
}
}
public KeyPairStrings getKeyPair() throws NoSuchAlgorithmException{
KeyPairStrings keyPairStrings = new RSA.KeyPairStrings();
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
KeyPair kp = kpg.genKeyPair();
PublicKey publicKey = kp.getPublic();
PrivateKey privateKey = kp.getPrivate();
byte[] publicKeyBytes = publicKey.getEncoded();
byte[] privateKeyBytes = privateKey.getEncoded();
keyPairStrings.pubKey = bytesToString(publicKeyBytes);
keyPairStrings.privKey = bytesToString(privateKeyBytes);
return keyPairStrings ;
}
public String encrypt(String text , String pubKey) throws NoSuchAlgorithmException, NoSuchPaddingException, IllegalBlockSizeException, BadPaddingException, InvalidKeyException{
byte[] pubKeyByte = stringToBytes(pubKey) ;
KeyFactory kf = KeyFactory.getInstance("RSA");
PublicKey publicKey = null;
try {
publicKey = kf.generatePublic(new X509EncodedKeySpec(pubKeyByte));
} catch (InvalidKeySpecException e) {
e.printStackTrace();
}
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey );
byte[] encryptedBytes = cipher.doFinal(text.getBytes());
String encrypted = bytesToString(encryptedBytes);
return encrypted;
}
public String decrypt(String encryptedText , String privKey) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
byte[] privKeyByte = stringToBytes(privKey) ;
KeyFactory kf = KeyFactory.getInstance("RSA");
PrivateKey privateKey = null;
try {
privateKey = kf.generatePrivate(new PKCS8EncodedKeySpec(privKeyByte));
} catch (InvalidKeySpecException e) {
e.printStackTrace();
}
String decrypted;
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] decryptedBytes = cipher.doFinal(stringToBytes(encryptedText));
decrypted = new String(decryptedBytes);
return decrypted;
}
public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeyException, NoSuchPaddingException, IllegalBlockSizeException, BadPaddingException {
String text = "hello" ;
RSA rsa = new RSA();
KeyPairStrings keyPairStrings = rsa.getKeyPair() ;
System.out.println(keyPairStrings);
String encrypted = rsa.encrypt(text, keyPairStrings.getPubKey());
System.out.println("encrypted : "+encrypted);
String textResult = rsa.decrypt(encrypted, keyPairStrings.getPrivKey());
System.out.println("textResult : "+textResult);
}
public static String bytesToString(byte[] b) {
byte[] b2 = new byte[b.length + 1];
b2[0] = 1;
System.arraycopy(b, 0, b2, 1, b.length);
return new BigInteger(b2).toString(36);
}
public byte[] stringToBytes(String s) {
byte[] b2 = new BigInteger(s, 36).toByteArray();
return Arrays.copyOfRange(b2, 1, b2.length);
}
}

Instead of this (which only reads the first character):
int plaintext;
plaintext = System.in.read();
bplaintext = BigInteger.valueOf((long) plaintext);
Use this (to read the string):
byte[] plaintext;
plaintext = new Scanner(System.in).nextLine().getBytes();
bplaintext = new BigInteger(plaintext);
Then add this to the end (to convert the decrypted BigInteger back to a string)
System.out.println("Original String: " + new String(bplaintext.toByteArray()));

Encrypt Decrypt my own key not generated java

I am new to cryptography, so I have a question:
How can I create my own key (let`s say like a string "1234"). Because I need to encrypt a string with a key (defined by me), save the encrypted string in a database and when I want to use it, take it from the database and decrypt it with the key known by me.
I have this code :
import java.security.InvalidKeyException;
import java.security.*;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESedeKeySpec;
public class LocalEncrypter {
private static String algorithm = "PBEWithMD5AndDES";
//private static Key key = null;
private static Cipher cipher = null;
private static SecretKey key;
private static void setUp() throws Exception {
///key = KeyGenerator.getInstance(algorithm).generateKey();
SecretKeyFactory factory = SecretKeyFactory.getInstance(algorithm);
String pass1 = "thisIsTheSecretKeyProvidedByMe";
byte[] pass = pass1.getBytes();
SecretKey key = factory.generateSecret(new DESedeKeySpec(pass));
cipher = Cipher.getInstance(algorithm);
}
public static void main(String[] args)
throws Exception {
setUp();
byte[] encryptionBytes = null;
String input = "1234";
System.out.println("Entered: " + input);
encryptionBytes = encrypt(input);
System.out.println(
"Recovered: " + decrypt(encryptionBytes));
}
private static byte[] encrypt(String input)
throws InvalidKeyException,
BadPaddingException,
IllegalBlockSizeException {
cipher.init(Cipher.ENCRYPT_MODE, key);
byte[] inputBytes = input.getBytes();
return cipher.doFinal(inputBytes);
}
private static String decrypt(byte[] encryptionBytes)
throws InvalidKeyException,
BadPaddingException,
IllegalBlockSizeException {
cipher.init(Cipher.DECRYPT_MODE, key);
byte[] recoveredBytes =
cipher.doFinal(encryptionBytes);
String recovered =
new String(recoveredBytes);
return recovered;
}
}
Exception in thread "main" java.security.spec.InvalidKeySpecException: Invalid key spec
at com.sun.crypto.provider.PBEKeyFactory.engineGenerateSecret(PBEKeyFactory.java:114)
at javax.crypto.SecretKeyFactory.generateSecret(SecretKeyFactory.java:335)
at LocalEncrypter.setUp(LocalEncrypter.java:22)
at LocalEncrypter.main(LocalEncrypter.java:28)

A KeyGenerator generates random keys. Since you know the secret key, what you need is a SecretKeyFactory. Get an instance for your algorithm (DESede), and then call its generateSecret méthode with an instance of DESedeKeySpec as argument:
SecretKeyFactory factory = SecretKeyFactory.getInstance("DESede");
SecretKey key = factory.generateSecret(new DESedeKeySpec(someByteArrayContainingAtLeast24Bytes));
Here is a complete example that works. As I said, DESedeKeySpec must be used with the DESede algorithm. Using a DESede key with PBEWithMD5AndDES makes no sense.
public class EncryptionTest {
public static void main(String[] args) throws Exception {
byte[] keyBytes = "1234567890azertyuiopqsdf".getBytes("ASCII");
DESedeKeySpec keySpec = new DESedeKeySpec(keyBytes);
SecretKeyFactory factory = SecretKeyFactory.getInstance("DESede");
SecretKey key = factory.generateSecret(keySpec);
byte[] text = "Hello world".getBytes("ASCII");
Cipher cipher = Cipher.getInstance("DESede");
cipher.init(Cipher.ENCRYPT_MODE, key);
byte[] encrypted = cipher.doFinal(text);
cipher = Cipher.getInstance("DESede");
cipher.init(Cipher.DECRYPT_MODE, key);
byte[] decrypted = cipher.doFinal(encrypted);
System.out.println(new String(decrypted, "ASCII"));
}
}

Well, I found the solution after combining from here and there. The encrypted result will be formatted as Base64 String for safe saving as xml file.
package cmdCrypto;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESedeKeySpec;
import javax.xml.bind.DatatypeConverter;
public class CmdCrypto {
public static void main(String[] args) {
try{
final String strPassPhrase = "123456789012345678901234"; //min 24 chars
String param = "No body can see me";
System.out.println("Text : " + param);
SecretKeyFactory factory = SecretKeyFactory.getInstance("DESede");
SecretKey key = factory.generateSecret(new DESedeKeySpec(strPassPhrase.getBytes()));
Cipher cipher = Cipher.getInstance("DESede");
cipher.init(Cipher.ENCRYPT_MODE, key);
String str = DatatypeConverter.printBase64Binary(cipher.doFinal(param.getBytes()));
System.out.println("Text Encryted : " + str);
cipher.init(Cipher.DECRYPT_MODE, key);
String str2 = new String(cipher.doFinal(DatatypeConverter.parseBase64Binary(str)));
System.out.println("Text Decryted : " + str2);
} catch(Exception e) {
e.printStackTrace();
}
}
}