RSAHelper.cs

using System;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.OpenSsl;
using Org.BouncyCastle.Security;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace RSA_Angular_with_.net.Helper
{
    public class RsaHelper
    {
        private readonly RSACryptoServiceProvider _privateKey;
        private readonly RSACryptoServiceProvider _publicKey;

        public RsaHelper()
        {
            string public_pem = @"C:\OpenSSL\bin\posvendor.pub.pem";
            string private_pem = @"C:\OpenSSL\bin\posvendor.key.pem";

            _publicKey = GetPublicKeyFromPemFile(public_pem);
            _privateKey = GetPrivateKeyFromPemFile(private_pem);

        }

        public string Encrypt(string text)
        {
            var encryptedBytes =_publicKey.Encrypt(Encoding.UTF8.GetBytes(text), false);
            return Convert.ToBase64String(encryptedBytes);
        }

        public string Decrypt(string encrypted)
        {
            var decryptedBytes = _privateKey.Decrypt(Convert.FromBase64String(encrypted), false);
            return Encoding.UTF8.GetString(decryptedBytes, 0, decryptedBytes.Length);
        }

        private RSACryptoServiceProvider GetPrivateKeyFromPemFile(string filePath)
        {
            using (TextReader privateKeyTextReader = new StringReader(File.ReadAllText(filePath)))
            {
                AsymmetricCipherKeyPair readKeyPair = (AsymmetricCipherKeyPair)new PemReader(privateKeyTextReader).ReadObject();

                RSAParameters rsaParams = DotNetUtilities.ToRSAParameters((RsaPrivateCrtKeyParameters)readKeyPair.Private);
                RSACryptoServiceProvider csp = new RSACryptoServiceProvider();
                csp.ImportParameters(rsaParams);
                return csp;
            }
        }

        private RSACryptoServiceProvider GetPublicKeyFromPemFile(String filePath)
        {
            using (TextReader publicKeyTextReader = new StringReader(File.ReadAllText(filePath)))
            {
                RsaKeyParameters publicKeyParam = (RsaKeyParameters)new PemReader(publicKeyTextReader).ReadObject();

                RSAParameters rsaParams = DotNetUtilities.ToRSAParameters((RsaKeyParameters)publicKeyParam);

                RSACryptoServiceProvider csp = new RSACryptoServiceProvider();
                csp.ImportParameters(rsaParams);
                return csp;
            }
        }
    }
}