C#中使用OpenSSL的公钥加密/私钥解密

在C#中进行公钥加密/私钥解密，需要用RSACryptoServiceProvider，但是它不支持由OpenSSL生成的公钥/私钥字符串。

比如这样的公钥/私钥对（ 公私钥生成方法见 http://travistidwell.com/jsencrypt/ ）：

公钥

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC7PyjMEuniN6BPn8oqzIZ6AO1N
jSTO9R3adCCIwKfKIEoWXXM+tHDpktdPKSaAsWJPTNAGvEvtxOfzXib/EMXKqD0e
Uy5MatfpRjRdf1hJVimmfrb09Qx2j7CsKLy7nD23m4xubdYBwvkjMwt/L3JxB5D6
qryW1wei/j1c+/OCxQIDAQAB
-----END PUBLIC KEY-----

私钥

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

网上有牛人通过解析公钥/私钥字符串，将之导入到RSACryptoServiceProvider中（原文链接已不存在）。

我们就是使用这位牛人的代码解决了这个问题，实际使用的代码如下：

public class RSACryptoService
{
    private RSACryptoServiceProvider _privateKeyRsaProvider;
    private RSACryptoServiceProvider _publicKeyRsaProvider;

    public RSACryptoService(string privateKey, string publicKey = null)
    {
        if (!string.IsNullOrEmpty(privateKey))
        {
            _privateKeyRsaProvider = CreateRsaProviderFromPrivateKey(privateKey);
        }

        if (!string.IsNullOrEmpty(publicKey))
        {
            _publicKeyRsaProvider = CreateRsaProviderFromPublicKey(publicKey);
        }
    }

    public string Decrypt(string cipherText)
    {
        if (_privateKeyRsaProvider == null)
        {
            throw new Exception("_privateKeyRsaProvider is null");
        }
        return Encoding.UTF8.GetString(_privateKeyRsaProvider.Decrypt(System.Convert.FromBase64String(cipherText), false));
    }

    public string Encrypt(string text)
    {
        if (_publicKeyRsaProvider == null)
        {
            throw new Exception("_publicKeyRsaProvider is null");
        }
        return Convert.ToBase64String(_publicKeyRsaProvider.Encrypt(Encoding.UTF8.GetBytes(text), false));
    }

    private RSACryptoServiceProvider CreateRsaProviderFromPrivateKey(string privateKey)
    {
        var privateKeyBits = System.Convert.FromBase64String(privateKey);

        var RSA = new RSACryptoServiceProvider();
        var RSAparams = new RSAParameters();

        using (BinaryReader binr = new BinaryReader(new MemoryStream(privateKeyBits)))
        {
            byte bt = 0;
            ushort twobytes = 0;
            twobytes = binr.ReadUInt16();
            if (twobytes == 0x8130)
                binr.ReadByte();
            else if (twobytes == 0x8230)
                binr.ReadInt16();
            else
                throw new Exception("Unexpected value read binr.ReadUInt16()");

            twobytes = binr.ReadUInt16();
            if (twobytes != 0x0102)
                throw new Exception("Unexpected version");

            bt = binr.ReadByte();
            if (bt != 0x00)
                throw new Exception("Unexpected value read binr.ReadByte()");

            RSAparams.Modulus = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.Exponent = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.D = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.P = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.Q = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.DP = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.DQ = binr.ReadBytes(GetIntegerSize(binr));
            RSAparams.InverseQ = binr.ReadBytes(GetIntegerSize(binr));
        }

        RSA.ImportParameters(RSAparams);
        return RSA;
    }

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

        if (bt == 0x81)
            count = binr.ReadByte();
        else
            if (bt == 0x82)
            {
                highbyte = binr.ReadByte();
                lowbyte = binr.ReadByte();
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                count = BitConverter.ToInt32(modint, 0);
            }
            else
            {
                count = bt;
            }

        while (binr.ReadByte() == 0x00)
        {
            count -= 1;
        }
        binr.BaseStream.Seek(-1, SeekOrigin.Current);
        return count;
    }
        
    private RSACryptoServiceProvider CreateRsaProviderFromPublicKey(string publicKeyString)
    {
        // encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
        byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
        byte[] x509key;
        byte[] seq = new byte[15];
        int x509size;

        x509key = Convert.FromBase64String(publicKeyString);
        x509size = x509key.Length;

        // ---------  Set up stream to read the asn.1 encoded SubjectPublicKeyInfo blob  ------
        using (MemoryStream mem = new MemoryStream(x509key))
        {
            using (BinaryReader binr = new BinaryReader(mem))  //wrap Memory Stream with BinaryReader for easy reading
            {
                byte bt = 0;
                ushort twobytes = 0;

                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;

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

                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8103) //data read as little endian order (actual data order for Bit String is 03 81)
                    binr.ReadByte();    //advance 1 byte
                else if (twobytes == 0x8203)
                    binr.ReadInt16();   //advance 2 bytes
                else
                    return null;

                bt = binr.ReadByte();
                if (bt != 0x00)     //expect null byte next
                    return null;

                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();
                byte lowbyte = 0x00;
                byte highbyte = 0x00;

                if (twobytes == 0x8102) //data read as little endian order (actual data order for Integer is 02 81)
                    lowbyte = binr.ReadByte();  // read next bytes which is bytes in modulus
                else if (twobytes == 0x8202)
                {
                    highbyte = binr.ReadByte(); //advance 2 bytes
                    lowbyte = binr.ReadByte();
                }
                else
                    return null;
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };   //reverse byte order since asn.1 key uses big endian order
                int modsize = BitConverter.ToInt32(modint, 0);

                int firstbyte = binr.PeekChar();
                if (firstbyte == 0x00)
                {   //if first byte (highest order) of modulus is zero, don't include it
                    binr.ReadByte();    //skip this null byte
                    modsize -= 1;   //reduce modulus buffer size by 1
                }

                byte[] modulus = binr.ReadBytes(modsize);   //read the modulus bytes

                if (binr.ReadByte() != 0x02)            //expect an Integer for the exponent data
                    return null;
                int expbytes = (int)binr.ReadByte();        // should only need one byte for actual exponent data (for all useful values)
                byte[] exponent = binr.ReadBytes(expbytes);

                // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                RSAParameters RSAKeyInfo = new RSAParameters();
                RSAKeyInfo.Modulus = modulus;
                RSAKeyInfo.Exponent = exponent;
                RSA.ImportParameters(RSAKeyInfo);

                return RSA;
            }

        }
    }

    private 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;
    }
}

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