using System;

using System.Security.Cryptography;

using System.Text;

//using System.IO;

​

class RsaEncryptionOaepSha1 {

    static void Main() {

    Console.WriteLine("RSA AES GCM hybrid encryption");

​

    Console.WriteLine("\nuses AES GCM 256 random key for the plaintext encryption");

    Console.WriteLine("and RSA OAEP SHA 1 2048 bit for the encryption of the random key\n");

​

    string plaintextString = "The quick brown fox jumps over the lazy dog";

    Console.WriteLine("plaintext: " + plaintextString);

​

    // # # # usually we would load the private and public key from a file or keystore # # #

    // # # # here we use hardcoded keys for demonstration - don't do this in real programs # # #

    string filenamePrivateKeyXml = "privatekey2048.xml";

    string filenamePublicKeyXml = "publickey2048.xml";

​

        try {

      // encryption

        Console.WriteLine("\n* * * Encryption * * *");

        string publicKeyLoad = loadRsaPublicKeyPem();

        // use this in production

        //string publicKeyLoad = File.ReadAllText(filenamePublicKeyXml);

        string completeCiphertextBase64 = rsaOaepSha1AesGcm256HybridStringEncryption(publicKeyLoad, plaintextString);

        Console.WriteLine("complete ciphertext: " + completeCiphertextBase64);

        Console.WriteLine("output is (Base64) encryptionKey : (Base64) nonce : (Base64) ciphertext : (Base64) gcmTag");

​

        // transport the encrypted data to recipient

​

        // receiving the encrypted data, decryption

        Console.WriteLine("\n* * * Decryption * * *");

        string completeCiphertextReceivedBase64 = completeCiphertextBase64;

        Console.WriteLine("completeCiphertextReceivedBase64: " + completeCiphertextReceivedBase64);

        string privateKeyLoad = loadRsaPrivateKeyPem();

        // use this in production

        //string privateKeyLoad = File.ReadAllText(filenamePrivateKeyXml);

        string decryptedText = rsaOaepSha1AesGcm256HybridStringDecryption(privateKeyLoad, completeCiphertextReceivedBase64);

        Console.WriteLine("plaintext: " + decryptedText);

        }

        catch(ArgumentNullException) {

            Console.WriteLine("The data was not RSA encrypted");

        }

    }

​

  static string rsaOaepSha1AesGcm256HybridStringEncryption (string publicKeyXml, string plaintext) {

    // generate random key

    byte[] encryptionKey = GenerateRandomAesKey();

    // encrypt plaintext

    string ciphertextBase64 = aesGcmEncryptToBase64(encryptionKey, plaintext);

    // encrypt the aes encryption key with the rsa public key

    string encryptionKeyBase64 = Base64Encoding(rsaEncryptionOaepSha1(publicKeyXml, encryptionKey));

    // complete output

    return encryptionKeyBase64 + ":" + ciphertextBase64;

  }

​

  static string rsaOaepSha1AesGcm256HybridStringDecryption (string privateKeyXml, string data) {

    String[] parts = data.Split(':');

    byte[] encryptedKeyReceived = Base64Decoding(parts[0]);

    byte[] nonce = Base64Decoding(parts[1]);

    byte[] encryptedData = Base64Decoding(parts[2]);

    byte[] gcmTag = Base64Decoding(parts[3]);

    // decrypt the encryption key with the rsa private key

    byte[] decryptionKey = rsaDecryptionOaepSha1(privateKeyXml, encryptedKeyReceived);

    return aesGcmDecrypt(decryptionKey, nonce, encryptedData, gcmTag);

  }

​

    static string aesGcmEncryptToBase64(byte[] key, string data) {

        byte[] plaintext = Encoding.UTF8.GetBytes(data);

        byte[] gcmTag = new byte[16];

        byte[] nonce = GenerateRandomNonce();

        byte[] cipherText = new byte[plaintext.Length];

        byte[] associatedData = new byte[0];

        using(var cipher = new AesGcm(key)) {

            cipher.Encrypt(nonce, plaintext, cipherText, gcmTag, associatedData);

            return Base64Encoding(nonce) + ":" + Base64Encoding(cipherText) + ":" + Base64Encoding(gcmTag);

        }

    }

​

    static string aesGcmDecrypt(byte[] key, byte[] nonce, byte[] ciphertext, byte[] gcmTag) {

        string decryptedtext;

        byte[] associatedData = new byte[0];

        byte[] decryptedData = new byte[ciphertext.Length];

        using(var cipher = new AesGcm(key)) {

            cipher.Decrypt(nonce, ciphertext, gcmTag, decryptedData, associatedData);

            decryptedtext = Encoding.UTF8.GetString(decryptedData, 0, decryptedData.Length);

            return decryptedtext;

        }

    }   

  static byte[] GenerateRandomAesKey() {

    RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();

    byte[] key = new byte[32];

    rngCsp.GetBytes(key);

    return key;

  }

​

    static byte[] GenerateRandomNonce() {

        RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();

        byte[] nonce = new byte[12];

        rngCsp.GetBytes(nonce);

        return nonce;

    }       

​

  public static byte[] rsaEncryptionOaepSha1(string publicKeyXml, byte[] plaintext) {

    RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(2048);

        RSAalg.PersistKeyInCsp = false;

        RSAalg.FromXmlString(publicKeyXml);

        return RSAalg.Encrypt(plaintext, true);

  }

​

  public static byte[] rsaDecryptionOaepSha1(string privateKeyXml, byte[] ciphertext) {

    RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(2048);

        RSAalg.PersistKeyInCsp = false;

        RSAalg.FromXmlString(privateKeyXml);

    return RSAalg.Decrypt(ciphertext, true);

  }

​

  static string Base64Encoding(byte[] input) {

    return Convert.ToBase64String(input);

  }

​

  static byte[] Base64Decoding(String input) {

    return Convert.FromBase64String(input);

  }

​

  public static string loadRsaPublicKeyPem() {

    return "<RSAKeyValue><Modulus>8EmWJUZ/Osz4vXtUU2S+0M4BP9+s423gjMjoX+qP1iCnlcRcFWxthQGN2CWSMZwR/vY9V0un/nsIxhZSWOH9iKzqUtZD4jt35jqOTeJ3PCSr48JirVDNLet7hRT37Ovfu5iieMN7ZNpkjeIG/CfT/QQl7R+kO/EnTmL3QjLKQNV/HhEbHS2/44x7PPoHqSqkOvl8GW0qtL39gTLWgAe801/w5PmcQ38CKG0oT2gdJmJqIxNmAEHkatYGHcMDtXRBpOhOSdraFj6SmPyHEmLBishaq7Jm8NPPNK9QcEQ3q+ERa5M6eM72PpF93g2p5cjKgyzzfoIV09Zb/LJ2aW2gQw==</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>";

  }

​

  public static string loadRsaPrivateKeyPem() {

    return "<RSAKeyValue><Modulus>8EmWJUZ/Osz4vXtUU2S+0M4BP9+s423gjMjoX+qP1iCnlcRcFWxthQGN2CWSMZwR/vY9V0un/nsIxhZSWOH9iKzqUtZD4jt35jqOTeJ3PCSr48JirVDNLet7hRT37Ovfu5iieMN7ZNpkjeIG/CfT/QQl7R+kO/EnTmL3QjLKQNV/HhEbHS2/44x7PPoHqSqkOvl8GW0qtL39gTLWgAe801/w5PmcQ38CKG0oT2gdJmJqIxNmAEHkatYGHcMDtXRBpOhOSdraFj6SmPyHEmLBishaq7Jm8NPPNK9QcEQ3q+ERa5M6eM72PpF93g2p5cjKgyzzfoIV09Zb/LJ2aW2gQw==</Modulus><Exponent>AQAB</Exponent><P>/8atV5DmNxFrxF1PODDjdJPNb9pzNrDF03TiFBZWS4Q+2JazyLGjZzhg5Vv9RJ7VcIjPAbMy2Cy5BUffEFE+8ryKVWfdpPxpPYOwHCJSw4Bqqdj0Pmp/xw928ebrnUoCzdkUqYYpRWx0T7YVRoA9RiBfQiVHhuJBSDPYJPoP34k=</P><Q>8H9wLE5L8raUn4NYYRuUVMa+1k4Q1N3XBixm5cccc/Ja4LVvrnWqmFOmfFgpVd8BcTGaPSsqfA4j/oEQp7tmjZqggVFqiM2mJ2YEv18cY/5kiDUVYR7VWSkpqVOkgiX3lK3UkIngnVMGGFnoIBlfBFF9uo02rZpC5o5zebaDIms=</Q><DP>BPXecL9Pp6u/0kwY+DcCgkVHi67J4zqka4htxgP04nwLF/o8PF0tlRfj0S7qh4UpEIimsxq9lrGvWOne6psYxG5hpGxiQQvgIqBGLxV/U2lPKEIb4oYAOmUTYnefBCrmSQW3v93pOP50dwNKAFcGWTDRiB/e9j+3EmZm/7iVzDk=</DP><DQ>rBWkAC/uLDf01Ma5AJMpahfkCZhGdupdp68x2YzFkTmDSXLJ/P15GhIQ+Lxkp2swrvwdL1OpzKaZnsxfTIXNddmEq8PEBSuRjnNzRjQaLnqjGMtTBvF3G5tWkjClb/MW2q4fgWUG8cusetQqQn2k/YQKAOh2jXXqFOstOZQc9Q0=</DQ><InverseQ>BtiIiTnpBkd6hkqJnHLh6JxBLSxUopFvbhlR37Thw1JN94i65dmtgnjwluvR/OMgzcR8e8uCH2sBn5od78vzgiDXsqITF76rJgeO639ILTA4MO3Mz+O2umrJhrkmgSk8hpRKA+5Mf9aE7dwOzHrc8hbj8J102zyYJIE6pOehrGE=</InverseQ><D>hXGYfOMFzXX/vds8HYQZpISDlSF3NmbTCdyZkIsHjndcGoSOTyeEOxV93MggxIRUSjAeKNjPVzikyr2ixdHbp4fAKnjsAjvcfnOOjBp09WW4QCi3/GCfUh0w39uhRGZKPjiqIj8NzBitN06LaoYD6MPg/CtSXiezGIlFn/Hs+MuEzNFu8PFDj9DhOFhfCgQaIgEEr+IHdnl5HuUVrwTnIBrEzZA/08Q0Gv86qQZctZWoD9hPGzeAC+RSMyGVJw6Ls8zBFf0eysB4spsu4LUom/WnZMdS1ls4eqsAX+7AdqPKBRuUVpr8FNyRM3s8pJUiGns6KFsPThtJGuH6c6KVwQ==</D></RSAKeyValue>";

  }

}

​