SHA256WithRSA

在上文中了解到SHA和RSA，工作中恰好用到扩展应用：SHA256WithRSA，本文总结下学习过程，备忘の
再提供另外一种方法，实现Java版pem密钥和.Net版xml密钥相互转换的方法

• RSA密钥：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私钥
    {
        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公钥
    {
        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密钥：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私钥
    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公钥
    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)  {
        //去掉证书的头部和尾部
        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，调用RSAKeyPemToXml()方法时，pemKey必须是格式正确的，否则调用报错。

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

扩展：从.pfx证书中提取公钥和私钥的方法

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);
}