SHA256WithRSA

在上文中瞭解到SHA和RSA，工做中剛好用到擴展應用：SHA256WithRSA，本文總結下學習過程，備忘の
再提供另一種方法，實現Java版pem密鑰和.Net版xml密鑰相互轉換的方法

密鑰轉換

準備：引入BouncyCastle.Crypto.dll

• RSA密鑰：Pem --> XML

public static string RSAKeyPemToXml(string pemKey, bool isPrivateKey)
{
    string rsaKey = string.Empty;
    object pemObject = null;
    RSAParameters rsaPara = new RSAParameters();
    using (var sReader = new StringReader(pemKey)) {
        var pemReader = new Org.BouncyCastle.OpenSsl.PemReader(sReader);
        pemObject = pemReader.ReadObject();//(AsymmetricCipherKeyPair)
    }
            
    if (isPrivateKey)//RSA私鑰
    {
        RsaPrivateCrtKeyParameters key = (RsaPrivateCrtKeyParameters)((AsymmetricCipherKeyPair)pemObject).Private;
        rsaPara = new RSAParameters {
            Modulus = key.Modulus.ToByteArrayUnsigned(),
            Exponent = key.PublicExponent.ToByteArrayUnsigned(),
            D = key.Exponent.ToByteArrayUnsigned(),
            P = key.P.ToByteArrayUnsigned(),
            Q = key.Q.ToByteArrayUnsigned(),
            DP = key.DP.ToByteArrayUnsigned(),
            DQ = key.DQ.ToByteArrayUnsigned(),
            InverseQ = key.QInv.ToByteArrayUnsigned(),  };
    }
    else//RSA公鑰
    {
        RsaKeyParameters key = (RsaKeyParameters)pemObject;
        rsaPara = new RSAParameters {
            Modulus = key.Modulus.ToByteArrayUnsigned(),
            Exponent = key.Exponent.ToByteArrayUnsigned(),  };
    }

    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    rsa.ImportParameters(rsaPara);
    using (StringWriter sw = new StringWriter()) {
        sw.Write(rsa.ToXmlString(isPrivateKey ? true : false));
        rsaKey = sw.ToString();
    }
    return rsaKey;
}

• RSA密鑰：XML --> Pem

public static string RSAKeyXmlToPem(string RSAKeyXml, bool isPrivateKey, bool replacefix)
{
    string pemKey = string.Empty;
    var rsa = new RSACryptoServiceProvider();
    rsa.FromXmlString(RSAKeyXml);

    RSAParameters rsaPara = new RSAParameters();
    RsaKeyParameters key = null;
    //RSA私鑰
    if (isPrivateKey)  {
        rsaPara = rsa.ExportParameters(true);
        key = new RsaPrivateCrtKeyParameters(
            new BigInteger(1, rsaPara.Modulus), new BigInteger(1, rsaPara.Exponent), new BigInteger(1, rsaPara.D),
            new BigInteger(1, rsaPara.P), new BigInteger(1, rsaPara.Q), new BigInteger(1, rsaPara.DP), new BigInteger(1, rsaPara.DQ),
            new BigInteger(1, rsaPara.InverseQ));
    }
    //RSA公鑰
    else  {
        rsaPara = rsa.ExportParameters(false);
        key = new RsaKeyParameters(false,
            new BigInteger(1, rsaPara.Modulus),  new BigInteger(1, rsaPara.Exponent));
    }

    using (TextWriter sw = new StringWriter()) {
        var pemWriter = new Org.BouncyCastle.OpenSsl.PemWriter(sw);
        pemWriter.WriteObject(key);
        pemWriter.Writer.Flush();
        pemKey = sw.ToString();
    }

    if (replacefix)  {
        //去掉證書的頭部和尾部
        pemKey = isPrivateKey ? pemKey.Replace("-----BEGIN RSA PRIVATE KEY-----", "").Replace("-----END RSA PRIVATE KEY-----", "") :
            pemKey.Replace("-----BEGIN PUBLIC KEY-----", "").Replace("-----END PUBLIC KEY-----", "");
        return pemKey.Replace("\n", "").Replace("\r", "");
    }
    else { return pemKey; }
}

注意，調用RSAKeyPemToXml()方法時，pemKey必須格式正確（帶先後綴且換行），不然調用報錯。

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

此外，調用RSAKeyXmlToPem()方法作私鑰轉換時，結果與原Pem密鑰不一致，慎用。

pfx證書

• PFX證書：由Public Key Cryptography Standards #12，PKCS#12標準定義，包含公鑰和私鑰的二進制格式的證書形式，以pfx做爲證書文件後綴名
• CER證書：證書中沒有私鑰，DER編碼二進制格式的證書文件/BASE64編碼格式的證書文件，以cer做爲證書文件後綴名

綜上所述：pfx證書文件中比cer文件中多了私鑰。
經過pfx證書實現數據簽名和驗籤

public static string Sign(string dataForSign, string priKeyFile, string keyPwd)
{
    var rsa = GetPrivateKey(priKeyFile, keyPwd);

    // Create a new RSACryptoServiceProvider
    var rsaClear = new RSACryptoServiceProvider();
    // Export RSA parameters from 'rsa' and import them into 'rsaClear'
    var paras = rsa.ExportParameters(true);
    rsaClear.ImportParameters(paras);

    using (var sha256 = new SHA256CryptoServiceProvider()) {
        var signData = rsaClear.SignData(Encoding.UTF8.GetBytes(dataForSign), sha256);
        return BytesToHex(signData);
    }
}
public bool VerifySign(string dataForSign, string signedData, string pubKeyFile)
{
    var rsa = GetPublicKey(pubKeyFile);
    using (var sha256 = new SHA256CryptoServiceProvider()) {
        return rsa.VerifyData(Encoding.UTF8.GetBytes(dataForSign), sha256, HexToBytes(signedData));
    }   
}

其中，從.pfx證書中提取公鑰和私鑰的方法

private static RSACryptoServiceProvider GetPrivateKey(string priKeyFile, string keyPwd) {
    var pc = new X509Certificate2(priKeyFile, keyPwd,
        X509KeyStorageFlags.Exportable | X509KeyStorageFlags.MachineKeySet);          
    return (RSACryptoServiceProvider)pc.PrivateKey; //return cert.PrivateKey.ToXmlString(true);
}

private static RSACryptoServiceProvider GetPublicKey(string pubKeyFile) {
    var pc = new X509Certificate2(pubKeyFile);
    return (RSACryptoServiceProvider)pc.PublicKey.Key; //return cert.PublicKey.Key.ToXmlString(false);
}

具體參見：.NET版SHA256WithRSA簽名驗籤，java版本參見：java版SHA256withRSA
關於如何生成數字證書，僅供參考：方法1，方法2
該文C#建立數字證書並導出爲pfx，並使用pfx進行非對稱加解密有時間能夠研究下。