c# - .NET 4.5 中 sslStream 的密码选择

Question

我正在尝试使用 .Net 的 sslStream 类创建 TLS1.1/TLS1.2 服务器。默认情况下，该流接受的唯一密码套件似乎是:

TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA 

我想启用这些的非 ECDHE 版本(即 TLS_RSA_WITH_AES_128_CBC_SHA256)。我在谷歌上搜索了一下，人们谈论通过修改默认的 SChannel 设置来更改密码套件——通过“SSL 密码套件顺序”或使用 CNG 函数:http://msdn.microsoft.com/en-us/library/windows/desktop/bb870930(v=vs.85).aspx

但是，我试过了，但我什么也做不了。使用上面链接的 C++ 代码列出启用的密码套件与 BCryptEnumContextFunctions() 显示我想要的密码套件在默认情况下已启用。我什至将 TLS_RSA_WITH_AES_128_CBC_SHA256 添加为最高优先级套件，并且 sslStream 仍然拒绝来自仅支持该密码的客户端的 TLS 连接(异常(exception):“客户端和服务器无法通信，因为它们不具备通用算法”)知道什么是发生在这里？

(顺便说一句，如果我的客户支持其中一个 ECDHE 密码套件，一切都很好)

其他人如何在 .Net 4.5 中实现 TLS？我应该看看开源解决方案吗？ SChannel 的包装器如何更直接地使用 CNG api？

Answer 1

我联系了 Microsoft 的技术支持，在使用他们专有的跟踪功能后，我发现我在服务器上安装的证书没有将其私钥标记为“交换 key ”。显然，证书库中每个公钥的私钥对应物都有特定的用途，这是允许的。在我的例子中，私钥只允许用于签名，不允许在 SSL/TLS 握手期间用于加密对称 key 。这意味着我的服务器只能支持 ECDHE 密码套件。

事实证明，您无法在证书 MMC 管理单元中检查私钥的启用使用。更糟糕的是，使用 sslStream 类，除了一般异常“客户端和服务器无法通信，因为它们不具备通用算法”之外，也无法确定握手失败的任何信息。

最后要提到的是我最初是如何设法安装带有受限私钥的服务器证书的。原来我是那样生成的。我使用 CertEnroll COM 接口(interface)以编程方式生成我导出的证书签名请求，具有证书颁发机构签名，并安装了证书颁发机构的响应。我用来生成证书签名请求的 C# 代码不小心创建了一个仅供签名使用的私钥。

根据我的经验，CertEnroll 接口(interface)很难使用，而且很难在线找到工作示例。因此，为了其他人的引用，我包括了我的 C# 代码，该代码生成一个 base64 编码的证书签名请求，用于 SSL/TLS 握手。在我的例子中，行 objPrivateKey.KeySpec = X509KeySpec.XCN_AT_KEYEXCHANGE; 丢失了。

using CERTENROLLLib;
using CERTCLILib;

public string GenerateRequest(string Subject, StoreLocation Location)
{
    //code originally came from: http://blogs.msdn.com/b/alejacma/archive/2008/09/05/how-to-create-a-certificate-request-with-certenroll-and-net-c.aspx
    //modified version of it is here: http://stackoverflow.com/questions/16755634/issue-generating-a-csr-in-windows-vista-cx509certificaterequestpkcs10
    //here is the standard for certificates: http://www.ietf.org/rfc/rfc3280.txt


    //the PKCS#10 certificate request (http://msdn.microsoft.com/en-us/library/windows/desktop/aa377505.aspx)
    CX509CertificateRequestPkcs10 objPkcs10 = new CX509CertificateRequestPkcs10();

    //assymetric private key that can be used for encryption (http://msdn.microsoft.com/en-us/library/windows/desktop/aa378921.aspx)
    CX509PrivateKey objPrivateKey = new CX509PrivateKey();

    //access to the general information about a cryptographic provider (http://msdn.microsoft.com/en-us/library/windows/desktop/aa375967.aspx)
    CCspInformation objCSP = new CCspInformation();

    //collection on cryptographic providers available: http://msdn.microsoft.com/en-us/library/windows/desktop/aa375967(v=vs.85).aspx
    CCspInformations objCSPs = new CCspInformations();

    CX500DistinguishedName objDN = new CX500DistinguishedName();

    //top level object that enables installing a certificate response http://msdn.microsoft.com/en-us/library/windows/desktop/aa377809.aspx
    CX509Enrollment objEnroll = new CX509Enrollment();
    CObjectIds objObjectIds = new CObjectIds();
    CObjectId objObjectId = new CObjectId();
    CObjectId objObjectId2 = new CObjectId();
    CX509ExtensionKeyUsage objExtensionKeyUsage = new CX509ExtensionKeyUsage();
    CX509ExtensionEnhancedKeyUsage objX509ExtensionEnhancedKeyUsage = new CX509ExtensionEnhancedKeyUsage();

    string csr_pem = null;

    //  Initialize the csp object using the desired Cryptograhic Service Provider (CSP)
    objCSPs.AddAvailableCsps();

    //Provide key container name, key length and key spec to the private key object
    objPrivateKey.ProviderName = providerName;
    objPrivateKey.Length = KeyLength;
    objPrivateKey.KeySpec = X509KeySpec.XCN_AT_KEYEXCHANGE; //Must flag as XCN_AT_KEYEXCHANGE to use this certificate for exchanging symmetric keys (needed for most SSL cipher suites)
    objPrivateKey.KeyUsage = X509PrivateKeyUsageFlags.XCN_NCRYPT_ALLOW_ALL_USAGES;                
    if (Location == StoreLocation.LocalMachine)
        objPrivateKey.MachineContext = true;
    else
        objPrivateKey.MachineContext = false; //must set this to true if installing to the local machine certificate store

    objPrivateKey.ExportPolicy = X509PrivateKeyExportFlags.XCN_NCRYPT_ALLOW_EXPORT_FLAG;    //must set this if we want to be able to export it later. 
    objPrivateKey.CspInformations = objCSPs;

    //  Create the actual key pair
    objPrivateKey.Create();

    //  Initialize the PKCS#10 certificate request object based on the private key.
    //  Using the context, indicate that this is a user certificate request and don't
    //  provide a template name
    if (Location == StoreLocation.LocalMachine)
        objPkcs10.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextMachine, objPrivateKey, "");
    else
        objPkcs10.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextUser, objPrivateKey, "");

    //Set hash to sha256
    CObjectId hashobj = new CObjectId();
    hashobj.InitializeFromAlgorithmName(ObjectIdGroupId.XCN_CRYPT_HASH_ALG_OID_GROUP_ID, ObjectIdPublicKeyFlags.XCN_CRYPT_OID_INFO_PUBKEY_ANY, AlgorithmFlags.AlgorithmFlagsNone, "SHA256");
    objPkcs10.HashAlgorithm = hashobj;

    // Key Usage Extension -- we only need digital signature and key encipherment for TLS:
    //  NOTE: in openSSL, I didn't used to request any specific extensions. Instead, I let the CA add them
    objExtensionKeyUsage.InitializeEncode(
        CERTENROLLLib.X509KeyUsageFlags.XCN_CERT_DIGITAL_SIGNATURE_KEY_USAGE |
        CERTENROLLLib.X509KeyUsageFlags.XCN_CERT_KEY_ENCIPHERMENT_KEY_USAGE
    );
    objPkcs10.X509Extensions.Add((CX509Extension)objExtensionKeyUsage);

    // Enhanced Key Usage Extension
    objObjectId.InitializeFromValue("1.3.6.1.5.5.7.3.1"); // OID for Server Authentication usage (see this: http://stackoverflow.com/questions/17477279/client-authentication-1-3-6-1-5-5-7-3-2-oid-in-server-certificates)
    objObjectId2.InitializeFromValue("1.3.6.1.5.5.7.3.2"); // OID for Client Authentication usage (see this: http://stackoverflow.com/questions/17477279/client-authentication-1-3-6-1-5-5-7-3-2-oid-in-server-certificates)
    objObjectIds.Add(objObjectId);
    objObjectIds.Add(objObjectId2);
    objX509ExtensionEnhancedKeyUsage.InitializeEncode(objObjectIds);
    objPkcs10.X509Extensions.Add((CX509Extension)objX509ExtensionEnhancedKeyUsage);

    //  Encode the name in using the Distinguished Name object
    // see here: http://msdn.microsoft.com/en-us/library/windows/desktop/aa379394(v=vs.85).aspx     
    objDN.Encode(
        Subject,
        X500NameFlags.XCN_CERT_NAME_STR_SEMICOLON_FLAG
    ); 

    // Assign the subject name by using the Distinguished Name object initialized above
    objPkcs10.Subject = objDN;

    //suppress extra attributes:
    objPkcs10.SuppressDefaults = true;

    // Create enrollment request
    objEnroll.InitializeFromRequest(objPkcs10);
    csr_pem = objEnroll.CreateRequest(
        EncodingType.XCN_CRYPT_STRING_BASE64
    );
    csr_pem = "-----BEGIN CERTIFICATE REQUEST-----\r\n" + csr_pem + "-----END CERTIFICATE REQUEST-----";

    return csr_pem;
}