Java tutorial
//package com.java2s; import java.math.BigInteger; import java.security.KeyFactory; import java.security.NoSuchAlgorithmException; import java.security.PrivateKey; import java.security.spec.InvalidKeySpecException; import java.security.spec.PKCS8EncodedKeySpec; import java.security.spec.RSAPublicKeySpec; public class Main { private static String RSA = "RSA"; public static PrivateKey getPrivateKey(byte[] keyBytes) throws NoSuchAlgorithmException, InvalidKeySpecException { PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes); KeyFactory keyFactory = KeyFactory.getInstance(RSA); PrivateKey privateKey = keyFactory.generatePrivate(keySpec); return privateKey; } public static PrivateKey getPrivateKey(String modulus, String privateExponent) throws NoSuchAlgorithmException, InvalidKeySpecException { BigInteger bigIntModulus = new BigInteger(modulus); BigInteger bigIntPrivateExponent = new BigInteger(privateExponent); RSAPublicKeySpec keySpec = new RSAPublicKeySpec(bigIntModulus, bigIntPrivateExponent); KeyFactory keyFactory = KeyFactory.getInstance(RSA); PrivateKey privateKey = keyFactory.generatePrivate(keySpec); return privateKey; } }