.NET RSA解密、签名、验签

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

namespace API.Tools
{
    /// <summary>
    /// 类名：RSAFromPkcs8
    /// 功能：RSA解密、签名、验签
    /// 详细：该类对Java生成的密钥进行解密和签名以及验签专用类，不需要修改
    /// 版本：2.0
    /// 修改日期：2011-05-10
    /// 说明：
    /// 以下代码只是为了方便商户测试而提供的样例代码，商户可以根据自己网站的需要，按照技术文档编写,并非一定要使用该代码。
    /// 该代码仅供学习和研究支付宝接口使用，只是提供一个参考。
    /// </summary>
    public sealed class Signatory
    {
        /// <summary>
        /// 签名(C#解释证书导出的，会出现“数据不正确”的错误)
        /// </summary>
        /// <param name="privateKey">私钥</param>
        /// <param name="content">需要签名的内容</param>
        /// <param name="encode">编码格式</param>
        /// <returns></returns>
        public static string sign(string privateKey, string content, Encoding encode)
        {
            byte[] Data = encode.GetBytes(content);
            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);
            MD5CryptoServiceProvider m5 = new MD5CryptoServiceProvider();

            byte[] signData = rsa.SignData(Data, m5);
            return Convert.ToBase64String(signData);
        }
/// <summary>
        /// 验证签名
        /// </summary>
        /// <param name="publicKey">公钥</param>
        /// <param name="content">需要验证的内容</param>
        /// <param name="signedString">签名结果</param>
        /// <param name="encode">编码格式</param>
        /// <returns></returns>
        public static bool verify(string publicKey, string content, string signedString, Encoding encode)
        {
            bool result = false;
            byte[] Data = encode.GetBytes(content);
            byte[] data = Convert.FromBase64String(signedString);
            RSAParameters paraPub = ConvertFromPublicKey(publicKey);
            RSACryptoServiceProvider rsaPub = new RSACryptoServiceProvider();
            rsaPub.ImportParameters(paraPub);

            MD5CryptoServiceProvider m5 = new MD5CryptoServiceProvider();
            result = rsaPub.VerifyData(Data, m5, data);
            return result;
        }

        /// <summary>
        /// 解析java生成的pem文件私钥
        /// </summary>
        /// <param name="pemstr"></param>
        /// <returns></returns>
        private static RSACryptoServiceProvider DecodePemPrivateKey(String pemstr)
        {
            byte[] pkcs8privatekey;
            pkcs8privatekey = Convert.FromBase64String(pemstr);
            if (pkcs8privatekey != null)
            {

                RSACryptoServiceProvider rsa = DecodePrivateKeyInfo(pkcs8privatekey);
                return rsa;
            }
            else
                return null;
        }

        private static RSACryptoServiceProvider DecodePrivateKeyInfo(byte[] pkcs8)
        {

            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];

            MemoryStream mem = new MemoryStream(pkcs8);
            int lenstream = (int)mem.Length;
            BinaryReader binr = new BinaryReader(mem);    //wrap Memory Stream with BinaryReader for easy reading
            byte bt = 0;
            ushort twobytes = 0;

            try
            {

                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130)    //data read as little endian order (actual data order for Sequence is 30 81)
                    binr.ReadByte();    //advance 1 byte
                else if (twobytes == 0x8230)
                    binr.ReadInt16();    //advance 2 bytes
                else
                    return null;

                bt = binr.ReadByte();
                if (bt != 0x02)
                    return null;

                twobytes = binr.ReadUInt16();

                if (twobytes != 0x0001)
                    return null;

                seq = binr.ReadBytes(15);        //read the Sequence OID
                if (!CompareBytearrays(seq, SeqOID))    //make sure Sequence for OID is correct
                    return null;

                bt = binr.ReadByte();
                if (bt != 0x04)    //expect an Octet string
                    return null;

                bt = binr.ReadByte();        //read next byte, or next 2 bytes is  0x81 or 0x82; otherwise bt is the byte count
                if (bt == 0x81)
                    binr.ReadByte();
                else
                    if (bt == 0x82)
                        binr.ReadUInt16();
                //------ at this stage, the remaining sequence should be the RSA private key

                byte[] rsaprivkey = binr.ReadBytes((int)(lenstream - mem.Position));
                RSACryptoServiceProvider rsacsp = DecodeRSAPrivateKey(rsaprivkey);
                return rsacsp;
            }

            catch (Exception)
            {
                return null;
            }

            finally { binr.Close(); }

        }

        private static bool CompareBytearrays(byte[] a, byte[] b)
        {
            if (a.Length != b.Length)
                return false;
            int i = 0;
            foreach (byte c in a)
            {
                if (c != b[i])
                    return false;
                i++;
            }
            return true;
        }

        private static RSACryptoServiceProvider DecodeRSAPrivateKey(byte[] privkey)
        {
            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;

            // ---------  Set up stream to decode the asn.1 encoded RSA private key  ------
            MemoryStream mem = new MemoryStream(privkey);
            BinaryReader binr = new BinaryReader(mem);    //wrap Memory Stream with BinaryReader for easy reading
            byte bt = 0;
            ushort twobytes = 0;
            int elems = 0;
            try
            {
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130)    //data read as little endian order (actual data order for Sequence is 30 81)
                    binr.ReadByte();    //advance 1 byte
                else if (twobytes == 0x8230)
                    binr.ReadInt16();    //advance 2 bytes
                else
                    return null;

                twobytes = binr.ReadUInt16();
                if (twobytes != 0x0102)    //version number
                    return null;
                bt = binr.ReadByte();
                if (bt != 0x00)
                    return null;

                //------  all private key components are Integer sequences ----
                elems = GetIntegerSize(binr);
                MODULUS = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                E = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                D = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                P = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                Q = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                DP = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                DQ = binr.ReadBytes(elems);

                elems = GetIntegerSize(binr);
                IQ = binr.ReadBytes(elems);

                // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                RSAParameters RSAparams = new RSAParameters();
                RSAparams.Modulus = MODULUS;
                RSAparams.Exponent = E;
                RSAparams.D = D;
                RSAparams.P = P;
                RSAparams.Q = Q;
                RSAparams.DP = DP;
                RSAparams.DQ = DQ;
                RSAparams.InverseQ = IQ;
                RSA.ImportParameters(RSAparams);
                return RSA;
            }
            catch (Exception)
            {
                return null;
            }
            finally { binr.Close(); }
        }

        private static int GetIntegerSize(BinaryReader binr)
        {
            byte bt = 0;
            byte lowbyte = 0x00;
            byte highbyte = 0x00;
            int count = 0;
            bt = binr.ReadByte();
            if (bt != 0x02)        //expect integer
                return 0;
            bt = binr.ReadByte();

            if (bt == 0x81)
                count = binr.ReadByte();    // data size in next byte
            else
                if (bt == 0x82)
                {
                    highbyte = binr.ReadByte();    // data size in next 2 bytes
                    lowbyte = binr.ReadByte();
                    byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                    count = BitConverter.ToInt32(modint, 0);
                }
                else
                {
                    count = bt;        // we already have the data size
                }

            while (binr.ReadByte() == 0x00)
            {    //remove high order zeros in data
                count -= 1;
            }
            binr.BaseStream.Seek(-1, SeekOrigin.Current);        //last ReadByte wasn‘t a removed zero, so back up a byte
            return count;
        }

        private static RSAParameters ConvertFromPublicKey(string pemFileConent)
        {

            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;
        }
    }
}

上面的类在平常使用的时候，是没有问题的，但，我们在对接第三方支付(易联支付)时，遇到一个非常刺手的，签名不通过。

• 签名证书，是从北京数字认证拿到，里面有一个文件xxxxx-Signature.pfx 和证书密码，我们需要从该文件中，使用openssl.exe工具，导出RSA公钥和私钥
• 导出的公钥，发给合作平台配上，私钥用于数据签名
• 签名时，使用导出的私钥进行。

问题来了，调用上面程序的sign()方法，解释私钥时，总报“数据不正解”或者“无效的私钥”之类的。更奇怪的是，该私钥在java下使用没有问题。联系了对方，对方试了好多几证书，只有我们的这个有问题。好吧，算倒霉吧。

解决方法：

.net里可以直接使用证书进行RSA签名：

        /// <summary>
        /// 签名，直接使用证书签名
        /// </summary>
        /// <param name="filePath"></param>
        /// <param name="password"></param>
        /// <param name="content"></param>
        /// <param name="encode"></param>
        /// <returns></returns>
        public static string sign(string filePath,string password, string content, Encoding encode)
        {
            byte[] Data = encode.GetBytes(content);

            X509Certificate2 myX509 = new X509Certificate2(filePath, password, X509KeyStorageFlags.Exportable);
            var rsa = (RSACryptoServiceProvider)myX509.PrivateKey;
            MD5CryptoServiceProvider m5 = new MD5CryptoServiceProvider();

            byte[] signData = rsa.SignData(Data, m5);
            return Convert.ToBase64String(signData);
        }

问题解决！