.NET 4.5 中 sslStream 的密码选择

Question

我正在尝试使用 .Net 的 sslStream 类创建一个 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）。我搜索了一下，人们谈论通过修改默认 SChannel 设置来更改密码套件——通过“SSL 密码套件顺序”或使用 CNG 功能：http://msdn.microsoft.com/en-us/library/windows/desktop/bb870930(v=vs.85).aspx

但是，我尝试了这个，但我无法正常工作。使用上面链接的 C++ 代码列出启用的密码套件 BCryptEnumContextFunctions() 表明我想要的密码套件默认启用。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（例外：“客户端和服务器无法通信，因为它们不具备通用算法”）知道什么是在这里进行吗？

（顺便说一句，如果我的客户支持其中一种 ECDHE 密码套件，那么一切正常）

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

Answer 1

我联系了微软的技术支持，在使用他们专有的跟踪功能后，发现我安装在服务器上的证书没有将它的私钥标记为“交换密钥”。显然，证书存储中每个公钥的私钥对应物都有其被允许的某些用途。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密钥。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用途。更糟糕的是，使用 sslStream 类，除了通用异常“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，我首先是如何设法安装带有受限私钥的服务器证书。事实证明，我是这样生成的。我正在使用 CertEnroll COM 接口以编程方式生成我导出的证书签名请求，具有证书颁发机构的签名，并安装了证书颁发机构的响应。我用于生成证书签名请求的 C# 代码意外创建了一个仅启用用于签名的私钥。

根据我的经验，CertEnroll 界面很难使用，而且很难在网上找到有效的示例。因此，为了其他人的参考，我将包含我的 C# 代码，该代码生成用于 SSL/TLS 握手的 base64 编码证书签名请求功能。就我而言，objPrivateKey.KeySpec = X509KeySpec.XCN_AT_KEYEXCHANGE; 行不见了。

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;
}