public key RSA encrption in dotnet c#

Question

I'm integrating a 3rd party API, where they want us to send some fields encrypted using their public key. I've seen RSACryptoServiceProvider and RSA class in dotnet but didn't find any way to put my public key explicitly.

What I want: string encryptedString Encrypt(string data, string publicKey, RSAEncryptionPadding.Pkcs1) { //code here. }

Answer 1

The following code is doing a complete round in RSA encryption & decryption with PKCS1 padding. As you can see I'm using hard coded keys in (dotnet) XML-format. As @Topaco already commented you can import the public key with other functions as well, depending on the key type.

As you probably get the public key in PEM-format ("-----BEGIN PUBLIC KEY-----...") you can use an online service like https://superdry.apphb.com/tools/online-rsa-key-converter to convert the PEM-key to a XML key (never ever do this with a private key!!).

This is the output of my sample program, you can run it in my live fiddle as well: https://dotnetfiddle.net/1LyKFB

RSA 2048 encryption PKCS1 string
plaintext: The quick brown fox jumps over the lazy dog

* * * encrypt the plaintext with the RSA public key * * *
ciphertextBase64: 7S7u+43NwYNV6041R0FlLMGvcJ/fRLPs4KQunUpa09XMk09Hzmzi6f0PYsoo5Bi8Y+kxYq0ocg+5BRCwyXV8MiH07ABzpGN9dDiijH16o5SJbDqN+8wC6PDJXirSY/8xj+4CPMbM4uFZI0wuWUGc5VchQ7UhgOg0fGo2nU3i2+UvDk9MSaU7V9GxfqHt03T92D0O7alXcak+Zm4khnzyONDzl9atlRdH5Gvm+BKy6Pi5ntoJj7BWcIhHF9qyKpUOkhN8shC3gGj/XpWfQpXs/inPXyR0DjrbtJ6MLIG+ScgCIMTB90L6L/r8pR0I1JJ0jAl+DR3U0V1DX7xPsV+utA==

* * * decrypt the ciphertext with the RSA private key * * *
ciphertextReceivedBase64: 7S7u+43NwYNV6041R0FlLMGvcJ/fRLPs4KQunUpa09XMk09Hzmzi6f0PYsoo5Bi8Y+kxYq0ocg+5BRCwyXV8MiH07ABzpGN9dDiijH16o5SJbDqN+8wC6PDJXirSY/8xj+4CPMbM4uFZI0wuWUGc5VchQ7UhgOg0fGo2nU3i2+UvDk9MSaU7V9GxfqHt03T92D0O7alXcak+Zm4khnzyONDzl9atlRdH5Gvm+BKy6Pi5ntoJj7BWcIhHF9qyKpUOkhN8shC3gGj/XpWfQpXs/inPXyR0DjrbtJ6MLIG+ScgCIMTB90L6L/r8pR0I1JJ0jAl+DR3U0V1DX7xPsV+utA==
decryptedData: The quick brown fox jumps over the lazy dog

Security warning: the following code has no exception handling and is for educational purpose only.

using System;
using System.Security.Cryptography;
using System.Text;
using System.IO;

public class RsaEncryptionOaepSha1 {
    public static void Main() {
    Console.WriteLine("RSA 2048 encryption PKCS1 string");
    string dataToEncryptString = "The quick brown fox jumps over the lazy dog";
    Console.WriteLine("plaintext: " + dataToEncryptString);

    // # # # 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* * * encrypt the plaintext with the RSA public key * * *");
        string publicKeyLoad = loadRsaPublicKeyPem();
        // use this in production
        //string publicKeyLoad = File.ReadAllText(filenamePublicKeyXml);
        byte[] dataToEncrypt = Encoding.UTF8.GetBytes(dataToEncryptString);
        string ciphertextBase64 = Base64Encoding(rsaEncryptionPkcs1(publicKeyLoad, dataToEncrypt));
        //string ciphertextBase64 = "";
        Console.WriteLine("ciphertextBase64: " + ciphertextBase64);

        // transport the encrypted data to recipient

        // receiving the encrypted data, decryption
        Console.WriteLine("\n* * * decrypt the ciphertext with the RSA private key * * *");
        string ciphertextReceivedBase64 = ciphertextBase64;
        Console.WriteLine("ciphertextReceivedBase64: " + ciphertextReceivedBase64);
        string privateKeyLoad = loadRsaPrivateKeyPem();
        // use this in production
        //string privateKeyLoad = File.ReadAllText(filenamePrivateKeyXml);
        byte[] ciphertextReceived = Base64Decoding(ciphertextReceivedBase64);
        byte[] decryptedtextByte = rsaDecryptionPkcs1(privateKeyLoad, ciphertextReceived);
        Console.WriteLine("decryptedData: " + Encoding.UTF8.GetString(decryptedtextByte, 0, decryptedtextByte.Length));
        }
        catch(ArgumentNullException) {
            Console.WriteLine("The data was not RSA encrypted");
        }
    }

  public static byte[] rsaEncryptionPkcs1(string publicKeyXml, byte[] plaintext) {
    RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(2048);
        RSAalg.PersistKeyInCsp = false;
        RSAalg.FromXmlString(publicKeyXml);
        return RSAalg.Encrypt(plaintext, false);
  }

  public static byte[] rsaDecryptionPkcs1(string privateKeyXml, byte[] ciphertext) {
    RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(2048);
        RSAalg.PersistKeyInCsp = false;
        RSAalg.FromXmlString(privateKeyXml);
    return RSAalg.Decrypt(ciphertext, false);
  }

  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>";
  }

}