RSA Encrypting & Descrypting in C# sample

Program.cs

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

namespace RsaEncryptionSample
{
    class Program
    {
        static void Main(string[] args)
        {

            var cryptoServiceProvider = new RSACryptoServiceProvider(2048); //2048 - Długość klucza
            var privateKey = cryptoServiceProvider.ExportParameters(true); //Generowanie klucza prywatnego
            var publicKey = cryptoServiceProvider.ExportParameters(false); //Generowanie klucza publiczny

            string publicKeyString = GetKeyString(publicKey);
            string privateKeyString = GetKeyString(privateKey);

            Console.WriteLine("KLUCZ PUBLICZNY: ");
            Console.WriteLine(publicKeyString);
            Console.WriteLine("-------------------------------------------");

            Console.WriteLine("KLUCZ PRYWATNY: ");
            Console.WriteLine(privateKeyString);
            Console.WriteLine("-------------------------------------------");

            string textToEncrypt = GenerateTestString(); 
            Console.WriteLine("TEKST DO ZASZYFROWANIA: ");
            Console.WriteLine(textToEncrypt);
            Console.WriteLine("-------------------------------------------");

            string encryptedText = Encrypt(textToEncrypt, publicKeyString); //Szyfrowanie za pomocą klucza publicznego
            Console.WriteLine("ZASZYFROWANY TEXT: ");
            Console.WriteLine(encryptedText);
            Console.WriteLine("-------------------------------------------");

            string decryptedText = Decrypt(encryptedText, privateKeyString); //Odszyfrowywanie za pomocą klucza prywatnego

            Console.WriteLine("ODSZYFROWANY TEXT: ");
            Console.WriteLine(decryptedText);

        }

        public static string GetKeyString(RSAParameters publicKey)
        {

            var stringWriter = new System.IO.StringWriter();
            var xmlSerializer = new System.Xml.Serialization.XmlSerializer(typeof(RSAParameters));
            xmlSerializer.Serialize(stringWriter, publicKey);
            return stringWriter.ToString();
        }

        public static string Encrypt(string textToEncrypt, string publicKeyString)
        {
            var bytesToEncrypt = Encoding.UTF8.GetBytes(textToEncrypt);

            using (var rsa = new RSACryptoServiceProvider(2048))
            {
                try
                {               
                    rsa.FromXmlString(publicKeyString.ToString());
                    var encryptedData = rsa.Encrypt(bytesToEncrypt, true);
                    var base64Encrypted = Convert.ToBase64String(encryptedData);
                    return base64Encrypted;
                }
                finally
                {
                    rsa.PersistKeyInCsp = false;
                }
            }
        }

        public static string Decrypt(string textToDecrypt, string privateKeyString)
        {
            var bytesToDescrypt = Encoding.UTF8.GetBytes(textToDecrypt);

            using (var rsa = new RSACryptoServiceProvider(2048))
            {
                try
                {

                    // server decrypting data with private key                    
                    rsa.FromXmlString(privateKeyString);

                    var resultBytes = Convert.FromBase64String(textToDecrypt);
                    var decryptedBytes = rsa.Decrypt(resultBytes, true);
                    var decryptedData = Encoding.UTF8.GetString(decryptedBytes);
                    return decryptedData.ToString();
                }
                finally
                {
                    rsa.PersistKeyInCsp = false;
                }
            }
        }

        private static string GenerateTestString()
        {
            Guid opportinityId = Guid.NewGuid();
            Guid systemUserId = Guid.NewGuid();
            string currentTime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");

            StringBuilder sb = new StringBuilder();
            sb.AppendFormat("opportunityid={0}", opportinityId.ToString());
            sb.AppendFormat("&systemuserid={0}", systemUserId.ToString());
            sb.AppendFormat("&currenttime={0}", currentTime);

            return sb.ToString(); 
        }
    }
}

Please share how we can use public key for decryption

You don't. Public keys are only for encryption.

You can actually, it is called "Signing" instead of encrypting for some weird reason.