RsaDecryptionOaepSha1.java

package RSA_Encryption_2048;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.OAEPParameterSpec;
import javax.crypto.spec.PSource;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.*;
import java.security.spec.MGF1ParameterSpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Base64;

public class RsaDecryptionOaepSha1 {
    public static void main(String[] args) throws GeneralSecurityException, IOException {
        System.out.println("RSA 2048 decryption OAEP SHA-1 string");

        // # # # usually we would load the private from a file or keystore # # #
        // # # # here we use a hardcoded key for demonstration - don't do this in real programs # # #
        String filenamePrivateKeyPem = "privatekey2048.pem";

        // receiving the encrypted data, decryption
        System.out.println("\n* * * decrypt the ciphertext with the RSA private key * * *");
        String ciphertextReceivedBase64 = "In0CE7VSJlr6PT+fl9SCejWhNZYioVn1UzYaqYUms7Y63oi4xK/2Qrgyi5a3CnvappM1MHdDaZVc+bDzl/iBiUslkHcF8lWGD4YdKuJgtfSS8WBRuIxz78EFhU3TfMU3y0v0bhUUj1/6ZdO/p9j8KcNbnpEB8A9YW+bZC1qOO8ibnTNbb3RHQekafz6r9oAYsILNga1pi9ZlyXQPYi7VpWAeZmUOq+MHEgD/Nkq/oxkyMo/yf5SVk1ig8M5Lr6arj22r2ePpQ8j3onmN7aOTCWUhZ7FdLm7IiRYebZ3MWPWozt9O6BSNjALLDXm7NfKaYcgQ+bVXrA4k1M9f4M9OEA==";
        System.out.println("ciphertextReceivedBase64: " + ciphertextReceivedBase64);
        PrivateKey privateKeyLoad = getPrivateKeyFromString(loadRsaPrivateKeyPem());
        // use this in production
        //PrivateKey privateKeyLoad = getPrivateKeyFromString(loadRsaKeyPemFile(filenamePrivateKeyPem));
        byte[] ciphertextReceived = base64Decoding(ciphertextReceivedBase64);
        byte[] decryptedtextByte = rsaDecryptionOaepSha1(privateKeyLoad, ciphertextReceived);
        System.out.println("decryptedtext: " + new String(decryptedtextByte, StandardCharsets.UTF_8));
    }

    public static byte[] rsaDecryptionOaepSha1 (PrivateKey privateKey, byte[] ciphertextByte) throws NoSuchAlgorithmException,
            NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, InvalidAlgorithmParameterException {
        byte[] decryptedtextByte = null;
        Cipher decryptCipher = Cipher.getInstance("RSA/ECB/OAEPWITHSHA-1ANDMGF1PADDING");
        //OAEPParameterSpec oaepParameterSpecJCE = new OAEPParameterSpec("SHA-256", "MGF1", MGF1ParameterSpec.SHA256, PSource.PSpecified.DEFAULT);
        OAEPParameterSpec oaepParameterSpecJCE = new OAEPParameterSpec("SHA1", "MGF1", MGF1ParameterSpec.SHA1, PSource.PSpecified.DEFAULT);
        decryptCipher.init(Cipher.DECRYPT_MODE, privateKey, oaepParameterSpecJCE);
        decryptedtextByte = decryptCipher.doFinal(ciphertextByte);
        return decryptedtextByte;
    }

    private static byte[] base64Decoding(String input) {
        return Base64.getDecoder().decode(input);
    }

    private static String loadRsaPrivateKeyPem() {
        // this is a sample key - don't worry !
        return "-----BEGIN PRIVATE KEY-----\n" +
                "MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQDwSZYlRn86zPi9\n" +
                "e1RTZL7QzgE/36zjbeCMyOhf6o/WIKeVxFwVbG2FAY3YJZIxnBH+9j1XS6f+ewjG\n" +
                "FlJY4f2IrOpS1kPiO3fmOo5N4nc8JKvjwmKtUM0t63uFFPfs69+7mKJ4w3tk2mSN\n" +
                "4gb8J9P9BCXtH6Q78SdOYvdCMspA1X8eERsdLb/jjHs8+gepKqQ6+XwZbSq0vf2B\n" +
                "MtaAB7zTX/Dk+ZxDfwIobShPaB0mYmojE2YAQeRq1gYdwwO1dEGk6E5J2toWPpKY\n" +
                "/IcSYsGKyFqrsmbw0880r1BwRDer4RFrkzp4zvY+kX3eDanlyMqDLPN+ghXT1lv8\n" +
                "snZpbaBDAgMBAAECggEBAIVxmHzjBc11/73bPB2EGaSEg5UhdzZm0wncmZCLB453\n" +
                "XBqEjk8nhDsVfdzIIMSEVEowHijYz1c4pMq9osXR26eHwCp47AI73H5zjowadPVl\n" +
                "uEAot/xgn1IdMN/boURmSj44qiI/DcwYrTdOi2qGA+jD4PwrUl4nsxiJRZ/x7PjL\n" +
                "hMzRbvDxQ4/Q4ThYXwoEGiIBBK/iB3Z5eR7lFa8E5yAaxM2QP9PENBr/OqkGXLWV\n" +
                "qA/YTxs3gAvkUjMhlScOi7PMwRX9HsrAeLKbLuC1KJv1p2THUtZbOHqrAF/uwHaj\n" +
                "ygUblFaa/BTckTN7PKSVIhp7OihbD04bSRrh+nOilcECgYEA/8atV5DmNxFrxF1P\n" +
                "ODDjdJPNb9pzNrDF03TiFBZWS4Q+2JazyLGjZzhg5Vv9RJ7VcIjPAbMy2Cy5BUff\n" +
                "EFE+8ryKVWfdpPxpPYOwHCJSw4Bqqdj0Pmp/xw928ebrnUoCzdkUqYYpRWx0T7YV\n" +
                "RoA9RiBfQiVHhuJBSDPYJPoP34kCgYEA8H9wLE5L8raUn4NYYRuUVMa+1k4Q1N3X\n" +
                "Bixm5cccc/Ja4LVvrnWqmFOmfFgpVd8BcTGaPSsqfA4j/oEQp7tmjZqggVFqiM2m\n" +
                "J2YEv18cY/5kiDUVYR7VWSkpqVOkgiX3lK3UkIngnVMGGFnoIBlfBFF9uo02rZpC\n" +
                "5o5zebaDImsCgYAE9d5wv0+nq7/STBj4NwKCRUeLrsnjOqRriG3GA/TifAsX+jw8\n" +
                "XS2VF+PRLuqHhSkQiKazGr2Wsa9Y6d7qmxjEbmGkbGJBC+AioEYvFX9TaU8oQhvi\n" +
                "hgA6ZRNid58EKuZJBbe/3ek4/nR3A0oAVwZZMNGIH972P7cSZmb/uJXMOQKBgQCs\n" +
                "FaQAL+4sN/TUxrkAkylqF+QJmEZ26l2nrzHZjMWROYNJcsn8/XkaEhD4vGSnazCu\n" +
                "/B0vU6nMppmezF9Mhc112YSrw8QFK5GOc3NGNBoueqMYy1MG8Xcbm1aSMKVv8xba\n" +
                "rh+BZQbxy6x61CpCfaT9hAoA6HaNdeoU6y05lBz1DQKBgAbYiIk56QZHeoZKiZxy\n" +
                "4eicQS0sVKKRb24ZUd+04cNSTfeIuuXZrYJ48Jbr0fzjIM3EfHvLgh9rAZ+aHe/L\n" +
                "84Ig17KiExe+qyYHjut/SC0wODDtzM/jtrpqyYa5JoEpPIaUSgPuTH/WhO3cDsx6\n" +
                "3PIW4/CddNs8mCSBOqTnoaxh\n" +
                "-----END PRIVATE KEY-----";
    }

    public static PrivateKey getPrivateKeyFromString(String key) throws GeneralSecurityException {
        String privateKeyPEM = key;
        privateKeyPEM = privateKeyPEM.replace("-----BEGIN PRIVATE KEY-----", "");
        privateKeyPEM = privateKeyPEM.replace("-----END PRIVATE KEY-----", "");
        privateKeyPEM = privateKeyPEM.replaceAll("[\\r\\n]+", "");
        byte[] encoded = Base64.getDecoder().decode(privateKeyPEM);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
        PrivateKey privKey = (PrivateKey) kf.generatePrivate(keySpec);
        return privKey;
    }

    private static String loadRsaKeyPemFile(String filename) throws IOException {
        return new String(Files.readAllBytes(Paths.get(filename)), StandardCharsets.UTF_8);
    }
}