Fundamental of certificate based authentication

I searched a lot and found many answer on how to implement certificate based authenticate in wcf. But my questions are related to fundamental of it.

While implementing Certificate based authentication on production, does client provides its certificate which server needs to add on its trusted people store? Or server provides a certificate (signed by server).

I guess while configuring wcf server, we just configure certificate location and store. We never bind it with any domain. So any client that present this certificate can access my service. And in case certificate needs to be bound to a domain. They why cannot we just allow all requests from that domain.

When client calls a wcf service, it present its certificate. Does this certificate only carry public key? And can this certificate by stolen (as it travels on network) and used by hacker to consume the web service.

I have idea about how ssl woks. In case of ssl, browser take care of all this stuff but in case of wcf service (when we want to allow only specific client to access our service) how it gets managed.

Thanks In advance.

Let me make it simple :

I want to create a web service and i want that three clients (A, B and C) can use it. I want to authenticate these three clients by certificate. While setting up, do these clients need to send their certificates to me. Or I have to create certificate for them? Will client share their private key as well (while setting up)
Do I need to put these certificates into trusted people store?
When they request for webservice, they will present their certificate (with public key only). If they present it with public key only, hackers can steal this public key and request for my web service. How will my webservice distinguish between hacker/actual client.

回答1:

While implementing Certificate based authentication on production, does client provides its certificate which server needs to add on its trusted people store? Or server provides a certificate (signed by server).

In a secure service, a server certificate is mandatory. Client certificate is optional. The server can be configured to ignore, accept, or require client certificates.

I guess while configuring wcf server, we just configure certificate location and store. We never bind it with any domain. So any client that present this certificate can access my service. And in case certificate needs to be bound to a domain. They why cannot we just allow all requests from that domain.

Not sure how you'd bind to a domain without a client certificate. You mean with reverse DNS lookup? That requires an IP address, and a malicious user can spoof it.

The typical means of restricting access via client certificates it to map one of the fields in the client certificate (typically the subject or domain) to a user account. You can have one-to-one mappings (each client certificate represents a single user) or many-to-one mappings (if the client has a certificate that is in a list, he is treated as a certain user). If the certificate isn't mapped, the user is treated as anonymous. More information here assuming you are using IIS.

When client calls a wcf service, it present its certificate. Does this certificate only carry public key? And can this certificate by stolen (as it travels on network) and used by hacker to consume the web service.

The certificate FILE that you handle during setup contains both the public and private key. The certificate itself is contained in that file; it contains a payload that includes the public key and a MAC signature, but does not include the private key.

The private key is put into secure storage and is never sent in any HTTP request. Only the certificate (and its public key) are sent over the wire. The whole file is not sent.

Edit to Respond to Further Questions

I want to create a web service and i want that three clients (A, B and C) can use it. I want to authenticate these three clients by certificate. While setting up, do these clients need to send their certificates to me. Or I have to create certificate for them?

During set up, a client certificate must be generated by a certificate authority (CA). You can actually serve the role as an intermediate CA (for production certificates) who derives his authority from a root CA (such as Verisign). In order to do that you must request a certificate from the root authority. They will issue you a certificate with its own public key, and give you a private key, so that you will have the ability to generate and digitally sign certificates of your own. You typically have to pay for this privilege.

In addition, you can become your own root CA! This is common during the development phase. Basically you generate your own public and private keys and start generating your own certificates. These are called self-signed certificates. The down side of being your own CA is that nobody will recognize your public key, so in order for anybody to use your certificates they would you have manually add you to their list of trusted root authorities.

Will client share their private key as well (while setting up)

No, nobody ever shares a private key with anybody, throughout the entire PKI. Ever. This is exactly why it is referred to as a private key. The only exception is when you are a certificate authority and you are generating a private key in order to create a certificate. In this case the private key must be carefully guarded during handling. It is never, ever sent over the wire as part of SSL communications.

Do I need to put these certificates into trusted people store?

Yes and no. If you are using a self-signed certificate, yes. If you are using a certificate that was signed by an CA that in turn has a certificate that was signed by a root CA, the root CA must also be in the list of trusted root authorities, but you probably don't have to add it. It should be there automatically. That is the whole purpose of using trusted root authorities-- everybody is supposed to know about them and should recognize their public keys. Root certificates are typically distributed to browsers automatically during installation and kept up to date using the browser's patch and update services.

When they request for webservice, they will present their certificate (with public key only). If they present it with public key only, hackers can steal this public key and request for my web service. How will my webservice distinguish between hacker/actual client.

This is a great question.

It's important to recognize that an SSL handshake includes a lot more than sharing certificates. There is also, among other things, a challenge/response step. Here's how it works:

Your server will generate a random number or time stamp ("challenge") and send it to your browser, challenging it to encrypt it. The browser will then encrypt the challenge using the private key (which it only has access to). This "response" is then sent back to the server for verification. The server uses the public key from the client certificate to decrypt the response. Since only the client has the private key, and since the public key is publicly known and verifiable (because it is contained in a signed and tamperproof certificate), the server can tell that the response had to have been encrypted by the client associated with the certificate. And because the challenge was generated by the server, and is different every time, a hacker cannot impersonate the client by replaying the response from a previous challenge.

回答2:

While implementing Certificate based authentication on production, does client provides its certificate which server needs to add on its trusted people store?

Yes, if the server asks for it, otherwise no.

Or server provides a certificate (signed by server).

Always. These aren't mutually exclusive. Both can happen.

I guess while configuring wcf server, we just configure certificate location and store. We never bind it with any domain. So any client that present this certificate can access my service. And in case certificate needs to be bound to a domain. They why cannot we just allow all requests from that domain.

I can't make head or tail of any of that.