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using System;
using System.Text;
using System.Security.Cryptography;
using System.Web;
using System.IO;
 
namespace Thinhunan.Cnblogs.Com.RSAUtility
{
    public class PemConverter
    {
        /// <summary>
        /// 将pem格式公钥转换为RSAParameters
        /// </summary>
        /// <param name="pemFileConent">pem公钥内容</param>
        /// <returns>转换得到的RSAParamenters</returns>
        public static RSAParameters ConvertFromPemPublicKey(string pemFileConent)
        {
            if (string.IsNullOrEmpty(pemFileConent))
            {
                throw new ArgumentNullException("pemFileConent", "This arg cann't be empty.");
            }
            pemFileConent = pemFileConent.Replace("-----BEGIN PUBLIC KEY-----", "").Replace("-----END PUBLIC KEY-----", "").Replace("\n", "").Replace("\r", "");
            byte[] keyData = Convert.FromBase64String(pemFileConent);
            if (keyData.Length < 162)
            {
                throw new ArgumentException("pem file content is incorrect.");
            }
            byte[] pemModulus = new byte[128];
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, 29, pemModulus, 0, 128);
            Array.Copy(keyData, 159, pemPublicExponent, 0, 3);
            RSAParameters para = new RSAParameters();
            para.Modulus = pemModulus;
            para.Exponent = pemPublicExponent;
            return para;
        }
 
        /// <summary>
        /// 将pem格式私钥转换为RSAParameters
        /// </summary>
        /// <param name="pemFileConent">pem私钥内容</param>
        /// <returns>转换得到的RSAParamenters</returns>
        public static RSAParameters ConvertFromPemPrivateKey(string pemFileConent)
        {
            if (string.IsNullOrEmpty(pemFileConent))
            {
                throw new ArgumentNullException("pemFileConent", "This arg cann't be empty.");
            }
            pemFileConent = pemFileConent.Replace("-----BEGIN RSA PRIVATE KEY-----", "").Replace("-----END RSA PRIVATE KEY-----", "").Replace("\n", "").Replace("\r","");
            byte[] keyData = Convert.FromBase64String(pemFileConent);
            if (keyData.Length < 609)
            {
                throw new ArgumentException("pem file content is incorrect.");
            }
 
            int index = 11;
            byte[] pemModulus = new byte[128];
            Array.Copy(keyData, index, pemModulus, 0, 128);
 
            index += 128;
            index += 2;//141
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, index, pemPublicExponent, 0, 3);
 
            index += 3;
            index += 4;//148
            byte[] pemPrivateExponent = new byte[128];
            Array.Copy(keyData, index , pemPrivateExponent, 0, 128);
 
            index += 128;
            index += ((int)keyData[index+1] == 64?2: 3);//279
            byte[] pemPrime1 = new byte[64];
            Array.Copy(keyData, index, pemPrime1, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//346
            byte[] pemPrime2 = new byte[64];
            Array.Copy(keyData, index , pemPrime2, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//412/413
            byte[] pemExponent1 = new byte[64];
            Array.Copy(keyData,index, pemExponent1, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//479/480
            byte[] pemExponent2 = new byte[64];
            Array.Copy(keyData, index, pemExponent2, 0, 64);
 
            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//545/546
            byte[] pemCoefficient = new byte[64];
            Array.Copy(keyData, index, pemCoefficient, 0, 64);
 
            RSAParameters para = new RSAParameters();
            para.Modulus = pemModulus;
            para.Exponent = pemPublicExponent;
            para.D = pemPrivateExponent;
            para.P = pemPrime1;
            para.Q = pemPrime2;
            para.DP = pemExponent1;
            para.DQ = pemExponent2;
            para.InverseQ = pemCoefficient;
            return para;
        }
         
    }
}
  
测试pem导成RSAParameters成功，使用通过：
using System;
using System.Security.Cryptography;
using System.Text;
using System.IO;
using System.Web;
 
 
namespace Thinhunan.Cnblogs.Com.RSAUtility
{
    class Program
    {
        #region keys
 
        const string PUBLICKEY =
@"-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDpsDr+W45aFHIkvotZaGK/THlF
FpuZfUtghhWkHAm3H7yvL42J4xHrTr6IeUDCl4eKe6qiIgvYSNoL3u4SERGOeYmV
1F+cocu9IMGnNoicbh1zVW6e8/iGT3xaYQizJoVuWA/TC/zdds2ihCJfHDBDsouO
CXecPapyWCGQNsH5sQIDAQAB
-----END PUBLIC KEY-----";
 
 
        const string PRIVATEKEY =
@"-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----";
 
        #endregion
 
        static void Main(string[] args)
        {           
             
            TestSignAndVerify();
             
        }
 
 
 
        public static void TestSignAndVerify()
        {
            //sign
            RSAParameters para = PemConverter.ConvertFromPemPrivateKey(PRIVATEKEY);
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.ImportParameters(para);
            byte[] testData = Encoding.UTF8.GetBytes("hello");
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            byte[] signData = rsa.SignData(testData, md5);
 
            //verify
            RSAParameters paraPub = PemConverter.ConvertFromPemPublicKey(PUBLICKEY);
            RSACryptoServiceProvider rsaPub = new RSACryptoServiceProvider();
            rsaPub.ImportParameters(paraPub);
            if (rsaPub.VerifyData(testData, md5, signData))
            {
                Console.WriteLine("ok");
            }
            else
            {
                Console.WriteLine("no");
            }
 
        }
 
    }
}