In the TLS handshake process, the Certificate Verify message will follow the Client Key Exchange message after the server requested a client certificate. The Certificate Verify contains a digital signature computed over all previous handshake messages including the type and length fields of the handshake messages. This process allows the client to prove that it owns the private key of the client certificate it sends to the server.
The idea came from a practical problem. There is an mTLS enabled server that conducts different action policies based on the client certificate received, for example, different welcome pages for different client certificates. If a layer-7 reverse proxy service like the load balancer is placed in front of the proxied server which also requires decrypting the TLS traffic. The proxied server can only get the client certificate information from the HTTP header (for example, set proxy_set_header with $ssl_client_cert variable in NGINX) which requires modifying the logic of the server.
A simple but very troublesome solution is the reverse proxy service stores all the client certificates and their private keys. The reverse proxy service will use the same client certificate it received during the mTLS handshake process to establish the mTLS connection with the proxied server.
Since the reverse proxy service can choose whether to trust the client or not with its own implementation, it is possible to forge the Certificate Verify message by asking the client to send a second Certificate Verify signature when the proxied server needs the reverse proxy service to do so (I know it's like a man-in-the-middle attack)?
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In our platform, the client will generate their own self-signed certificate. We will then validate the certificate external from the nginx. I use optional_no_ca and not verify the client with a trusted CA. I perform verification on the server side after nginx
I am now building the production environment with API Gateway and ALB. However, I do not know the equivalent of optional_no_ca. I want the client to verify the server cert but the client certificate should pass through to the server for some application checks.
I wrote a proxy server which works well. But when looking at the log, there are some weird requests like:
POST https://vortex.data.microsoft.com/collect/v1 HTTP/1.1
Also some GET over https. I think only CONNECT is allowed over https, am I wrong? If I am wrong, how to deal with these request? (I just dropped these requests in my app.)
Another thing maybe unrelated is all these requests are related to microsoft from the log.
There isn't any problem handling any HTTP Method with HTTPS within a proxy.
All the requests with https://-protocol will be automatically received and sent to port 443 if not indicated otherwise.
Independently if you have a server where you deployed a HAProxy, NGINX, Apache Web Server or that you literally wrote a proxy like this one in JavaScript, only thing you have to do is to literally proxy the requests to the destination server address.
Regarding the encryption, precisely HTTPS ensures that there are no eavesdroppers between the client and the actual target, so the Proxy would act as initial target and then this would transparently intercept the connection.
Client starts HTTPS session to Proxy
Proxy intercepts and returns its certificate, signed by a CA trusted by the client.
Proxy starts HTTPS session to Target
Target returns its certificate, signed by a CA trusted by the Proxy.
Proxy streams content, decrypt and re-encrypt with its certificate.
Basically it's a concatenation of two HTTPS sessions, one between the client and the proxy and other between the proxy and the final destination.
This is the question about HTTP CONNECT method.
I learned that after CONNECT request from client a TCP connection is established between proxy and remote server.
Then, at the step of SSL handshake, does the proxy evaluate and relay any http data from client up to at TCP level? So the data is not passed to application level of the proxy?
I understood that after SSL session establishment any data from client is encrypted and the proxy cannot read those. But how about the time before SSL session establishment, that is, SSL handshake step?
After the proxy has sent a successful response to the clients CONNECT request a normal proxy will forward all data between client and server without any changes. This includes the TLS handshake for HTTPS connections tunneled using CONNECT.
Note that there are proxies which do SSL interception (typically at firewalls). In this case the data are not blindly forwarded but the proxy will be an active man in the middle which means that the client does not receive the original certificate from the server and that the proxy will decrypt and maybe even modify the traffic between client and server.
The question is about HTTP vs HTTPS.
If I want to anonymously load a website that forces HTTPS, like Google.com, do I need an HTTPS proxies, or can I get away with HTTP proxies?
If your proxy is SOCKS it will not care what kind of socket is connecting through it. It has its own handshake and it does not care about what happens after the handshake. Whether after the SOCKS handshake an SSL handshake (HTTPS) is started it is not a SOCKS proxy problem, it will just pass through.
Several HTTP proxies on the other hand expect HTTP headers to guide them, such a HTTP proxy will not allow HTTPS since it needs to read the headers.
On the third hand (ekhm... well, foot?), an HTTP proxy that supports HTTP CONNECT can also setup the transfer of arbitrary data. Therefore such a proxy can setup any type of socket, which can have an SSL handshake, which can then be used for HTTPS transfer.
HTTP Proxy Server supports CONNECT verb which supports HTTPS connections within HTTP Proxy. You don't need special HTTPS proxy server or any other setup.
CONNECT verb allows you to create binary socket tunnel to any given IP:Port address. So any HTTP client (all browsers), will open secure tunnel and communicate securely over proxy server. However, no one cant control or see anything that is going through the tunnel unless they implement man in middle attack by sending you self-signed certificates.
Most firewall these days automatically implement man in middle self signed certificates that are deployed in work network, so you have to probably dig more to identify whether it is really secure or not. So it may not be that anonymous.
If you're trying to access a service anonymously, you won't get this by running your own proxy. It's not clear from the original question what is meant by "proxy", e.g. local service, or remote service. You won't get anonymity by surfing through a proxy that's on your network, unless it's something like a TOR proxy which relays out through the TOR network.
As for whether proxies can support HTTPS or not, that's been covered here, it would be unusual to find a proxy that doesn't support CONNECT. However if it's a remote anonymizing service you're using, I doubt they would do MitM, since you'd need to install the signing cert into your trusted root store, so they couldn't do that surreptitiously.
The JVM allows proxy properties http.proxyHost and http.proxyPort for specifying a HTTP proxy server and https.proxyHost and https.proxyPort for specifying a HTTPS proxy server .
I was wondering whether there are any advantages of using a HTTPS proxy server compared to a HTTP proxy server ?
Is accessing a https url via a HTTPS proxy less cumbersome than accesing it from a HTTP proxy ?
HTTP proxy gets a plain-text request and [in most but not all cases] sends a different HTTP request to the remote server, then returns information to the client.
HTTPS proxy is a relayer, which receives special HTTP request (CONNECT verb) and builds an opaque tunnel to the destination server (which is not necessarily even an HTTPS server). Then the client sends SSL/TLS request to the server and they continue with SSL handshake and then with HTTPS (if requested).
As you see, these are two completely different proxy types with different behavior and different design goals. HTTPS proxy can't cache anything as it doesn't see the request sent to the server. With HTTPS proxy you have a channel to the server and the client receives and validates server's certificate (and optionally vice versa). HTTP proxy, on the other hand, sees and has control over the request it received from the client.
While HTTPS request can be sent via HTTP proxy, this is almost never done because in this scenario the proxy will validate server's certificate, but the client will be able to receive and validate only proxy's certificate, and as name in the proxy's certificate will not match the address the socket connected to, in most cases an alert will be given and SSL handshake won't succeed (I am not going into details of how to try to address this).
Finally, as HTTP proxy can look into the request, this invalidates the idea of security provided by HTTPS channel, so using HTTP proxy for HTTPS requests is normally done only for debugging purposes (again we omit cases of paranoid company security policies which require monitoring of all HtTPS traffic of company employees).
Addition: also read my answer on the similar topic here.
There are no pros or cons.
And there are no "HTTPS proxy" server.
You can tell the protocol handlers which proxy server to use for different protocols. This can be done for http, https, ftp and socks. Not more and not less.
I can't tell you if you should use a different proxy for https connections or not. It depends.
I can only explain the difference of an http and https request to a proxy.
Since the HTTP Proxy (or web proxy) understands HTTP (hence the name), the client can just send the request to the proxy server instead of the actual destenation.
This does not work for HTTPS.
This is because the proxy can't make the TLS handshake, which happens at first.
Therefore the client must send a CONNECT request to the proxy.
The proxy establishes a TCP connection and just sends the packages forth and back without touching them.
So the TLS handshake happens between the client and destenation.
The HTTP proxy server does not see everything and does not validate destenation servers certificate whatsoever.
There can be some confusion with this whole http, https, proxy thing.
It is possible to connect to a HTTP proxy with https.
In this case, the communication between the client and the proxy is encrypted.
There are also so called TLS terminating or interception proxy servers like Squid's SSL Peek and Splice or burp, which see everything.
But this should not work out of the box, because the proxy uses own certificates which are not signed by trusted CAs.
References
https://docs.oracle.com/javase/8/docs/technotes/guides/net/proxies.html
https://parsiya.net/blog/2016-07-28-thick-client-proxying---part-6-how-https-proxies-work/
http://dev.chromium.org/developers/design-documents/secure-web-proxy
https://www.rfc-editor.org/rfc/rfc2817#section-5
https://www.rfc-editor.org/rfc/rfc7231#section-4.3.6
If you mean connecting to a HTTP proxy server over TLS by saying HTTPS proxy, then
I was wondering whether there are any advantages of using a HTTPS
proxy server compared to a HTTP proxy server ?
The advantage is that your client's connection to proxy server is encrypted. E.g. A firewall can't not see which host you use CONNECT method connect to.
Is accessing a https url via a HTTPS proxy less cumbersome than
accesing it from a HTTP proxy ?
Everything is the same except that with HTTPS proxy, brower to proxy server connection is encrypted.
But you need to deploy a certificate on your proxy server, like how a https website does, and use a pac file to configure the brower to enable Connecting to a proxy over SSL.
For more details and a practical example, check my question and answer here HTTPs proxy server only works in SwitchOmega
Unfortunately, "HTTPS proxy" has two distinct meanings:
A proxy that can forward HTTPS traffic to the destination. This proxy itself is using an HTTP protocol to set up the forwarding.
In case the browser is trying to connect to a website using HTTPS, the browser will send a CONNECT request to the proxy, and the proxy will set up a TCP connection with the website and mirror all TCP traffic sent on the connection from the browser to the proxy onto the connection between the proxy and the website, and similarly mirror the response TCP packet payload from the webite to the connection with the browser. Hypothetically, the same mechanism using CONNECT could be used with HTTP traffic, but practically speaking browsers don't do that. For HTTP traffic, they send the actual HTTP request to the proxy, including the full path in the HTTP command (as well as setting the Host header): https://stackoverflow.com/a/38259076/10026
So, by this definition, HTTPS Proxy is a proxy that understands the CONNECT directive and can support HTTPS traffic going between the browser and the website.
A proxy that uses HTTPS protocol to secure client communication.
In this mode (sometimes referred to as "Secure Proxy"), the browser uses the proxy's own certificate to perform TLS handshake with the proxy, and then sends either HTTP or HTTPS traffic, (including CONNECT requests), on that connection as per (1). So, the connection between the browser and the proxy is always protected with a TLS key derived using the proxy's certificate, regardless of whether the traffic itself is encrypted with a key negotiated between the browser and the website. If HTTPS traffic is proxied via a secure proxy, it is double-encrypted on the connection between the browser and the proxy.
For example, the Proxy Switcher Chrome plugin has two separate settings to control each of these funtionalities:
As of 2022, the option to use a secure proxy is not available in MacOS and Windows manual proxy configuration UI. But a secure proxy may be specified in a PAC file used in automatic proxy configuration using the HTTPS proxy directive. It is up to the consuming application to support the HTTPS directive; most major browsers, except Safari, and many desktop apps support it.
NOTE: Things get a bit more complicated because some proxies that proxy HTTPS traffic don't simply forward TCP packet payload, as described in (1), but act as Intercepting Proxies. Using a spoofed website certificate, they effectively perform a Man-in-the-Middle attack (well, it's not necessarily an attack because it's expected behavior). Whereas the browser thinks it's using the website's certificate to set up a TLS tunnel with a website, it's actually using a spoofed certificate to set up TLS tunnel with the proxy, and the proxy sets up the TLS tunnel with the website. Then proxy has visibility into the HTTPS requests/responses. But all of that is completely orthogonal to whether the proxy is acting as a secure proxy as per (2).