I am currently looking for the best way to establish a stateful and encrypted connection between a C# client and server application. First, I thought about using IPsec, but as it works on a low level (OSI: Internet Layer), I would be very hard to implement, if you want the functionality inside your program and don't want to rely on the OS.
What technologies would you recommend for this purpose? Is there some functionality already built into .NET (4.5)? It does not neccessarily have to be stateful, working with some kind of heartbeat would be a valid option, too.
You'll want to use a standard protocol such as SSL rather than trying to make your own. First the implementation will be much easier because the .NET framework will support it, and the transport protocol that runs underneath it is stateful (e.g. TCP). Second developing a cryptographic protocol that is secure is very difficult, and SSL has already been implemented so why reinvent the wheel?
SSL works by using PKI (Public Key Infrastructure) to generate a shared symmetric key. The handshake consists of a number of steps. First the client sends a request for a secure session, then the server responds with it's certificate, the client verifies the certificate by crawling up the ladder through the certificate authorities (e.g. Verisign, Thawte, GeoTrust etc...) or if it already trusts the server it can just accept the certificate that is self signed.... and once it finds the certificate is trustworthy it generates a symmetric key and picks an algorithm (e.g. AES, 3DES, RC4, IDEA etc...). The client then encrypts the key and algorithm being used with the public key, then the client sends that value to the server and a secure session can proceed using symmetric encryption which is much faster.
SSL itself is can be used in a stateful manner because it actually works over the transport layer in the OSI Model, HTTPS on the other hand is not a stateful protocol by design. HTTPS is HTTP over SSL so the two technically don't really have anything to do with each other, except that in HTTPS SSL is used to secure the application data that is being requested. With HTTPS as with HTTP once a request is made to the server it basically forgets about you (not exactly how it happens but for all intents and purposes you can think of it this way). I myself would prefer the use of HTTPS if you can get around having to have a stateful protocol. The main reason for doing so is so that I wouldn't have to write the code and possibly have a mistake in the implementation of SSL. All you have to do is build a WCF or REST based service that runs on IIS and get a certificate for your server.
That being said, if you still want to create your own SSL server that doesn't use HTTP on the application level you can use the TcpListener and TcpClient classes along with the SslStream class provided as part of .NET to create your own. MSDN has a good example of how to create an SSL server and client: http://msdn.microsoft.com/en-us/library/system.net.security.sslstream%28v=vs.110%29.aspx
Side Notes
Securing the transport of your data does not secure your app, do not make the mistake of thinking you get automatic security
If you choose to make your own server and client you can use either openssl to generate your certificate or you can use makecert which is part of .NET to make your certificate.
Just form a regular TCP connection between the applications, and write up a simple packet protocol (EG, 4 bytes indicate packet size, followed by packet data)
Except the data within this base-level packet is encrypted through System.Cryptography.AesManaged
If you have trouble encrypting the packets using AesManaged, try using The Encryptamajig - if that doesn't help, post further questions and we'll give you further specific help.
-- You can either have both sides know the password ahead of time (EG, tell the person at the other end the password in person), or quickly pass it unencrypted at the start of the connection (or, rather, encrypted with a default known password)
Not necessarily the best method but it should do the job.
Why not just the regular HTTPS? HTTP is just one level above TCP but it is far easier to work with and firewalls tend to be generally easy on HTTP/HTTPS ports namely 80 and 443. Of course, plain HTTP is not suitable for you but can you not use HTTPS instead of coming up with your own encrypted communication mechanism? In the client side (C#), all .NET classes such as HttpClient supports HTTPS very well. I quote Ayende in support of my suggestion to go with HTTP :)
Related
I have a Client & Server application set, both written in C# but some client versions might be distributed in other languages in the future. I want to protect my applications.
I was looking for some kind of advice to stop just random people sending messages to a server and acting like a client, what kind of validation can I put in place?
My client applications I distribute will be obfuscated but is this enough? I'm just looking for some advice in this situation, is it wise for me to add some kind of encryption other than SSL, or am I just being over protective and over curious? Any input is welcomed & accepted.
It is impossible to determine if you are communicating remotely with "your client" or another piece of software that also knows how to communicate in the way that your client does.
What you can do is ensure that you are communicating with someone that is authorized to communicate with you by using client certificates for your SSL session.
The server proves who it is to the client and the client proves who it is to your server. The security then rests in whoever holds the private key to the client certificate (and the password for this key file).
The C# SslStream Class has support for this. Namely the AuthenticateAsClient method is relevant here.
In summary, if your software is only secure when communicating with a client you wrote, then your software isn't secure period. Instead, design your server in such a way that you can serve client requests securely. Using authentication is one of these ways.
You would want to do two things....one is look up certificate pinning. Your app will validate your SSL cert to thwart man in the middle attacks and it makes it hard to circumvent. The other is when making requests to the server have some type of user name / password block on the server side script before the server side does anything so the requests will simply be discarded by the server if they are from an unknown source.
I'm currently developing a C# application that communicates between a client and server using TCP/IP. After connecting I'm swapping session based RSA public keys to then pass a session based AES symmetrical key. This all works fine and means I have a secure channel to communicate on.
The trouble now is that I need to ensure that the server and client are both the ones I wish to communicate with. Before anyone suggests SSL/TLS: I'm not connected to the Internet to allow the use of a root CA.
Would it be valid, that after establishing a secure channel between the client and server that I provide a simple challenge-response method? For example, if the client sends an identifier (GUID?) the server compares this value to known clients and accepts or rejects it, and the same is repeated in the opposite direction. As the data is encrypted and the encryption is session based is this a valid method of verification?
I understand that the storage of these identifiers is the weak point.
Before anyone suggests SSL/TLS: I'm not connected to the Internet to allow the use of a root CA.
Before you are re-inventing the wheel: you don't need root CA with SSL/TLS but can simply use self-signed certificates with key pinning. Public root CAs are only usually used because it scales much better to provide only few common CAs instead of exchanging all self-signed certificates (or their fingerprint) to all peers of the communication.
Apart from that it looks like you proposal assumes a secure connection already to check credentials which you then will use to verify that the connection is really secure. Or in short: to provide a secure connection you need a secure connection first.
I'm tasked with encryption of the network communication of our program and I've been thrown a wrench. I was going to use SslStream but my CTO would like to stay away from managing certificates. So I was wondering is there any other Stream that will encrypt data, or a way to dynamically generate certificates?
You could encrypt your data using a standard encryption algoithm (RSA, AES, PGP, etc.) as long as you control both endpoints. If not, you will need to use something like certificates since clients won't be able to otherwise decrypt. I'm not sure why your CTO would avoid certs, but nonetheless...
See this article for a good start: http://msdn.microsoft.com/en-us/library/0ss79b2x.aspx
Also note that WCF supports MANY means of communication encryption, many of which do not require certs.
WCF netTCPBinding - Is transport encryption enough?
Note finally that you cannot encrypt the message headers if you don't talk directly to the other party (ie: if there's anyone in the middle), since the middle part won't be able to decipher/route your message.
I'm writing a client/server application that requires the server needs to be able to authenticate the client and also requires all comms to be encrypted.
The mechanism to provide this needs to be self contained within the server and client application and also to be fully automated (no human interaction required). SSL seems to be the best way to do this and is also something I am familiar with using.
For each client that needs the client software deploying to it, I planned to create (on the fly) an MSI installer with the application, the clients certificate (signed by the server) and private key and the servers public certificate (so the clients can authenticate the server - the server certificate could be self signed).
I can generate the key for the client and make a CSR, but don't seem to be able to find a way of actually signing the CSR and generating a certificate for the client thou. I have looked into the Win32 Crypto API, but haven't managed to find any examples of how to actually sign a CSR and get a client certificate.
I know how to do all of this from the command line with the openssl tool, but am not sure of how to do it from within an application.
Please note that making system calls out to the openssl tool and passing in the parameters I know to work is not an option as it's a huge security risk to rely on the openssl tool not being compromised in any way. Doing it this way wouldn't for fill the self contained requirement.
I am going about this the right way, or is there a better way to achieve the same thing - basically authentication of the clients connecting to the server and a way of the connecting client to authenticate the server they connect to, all encrypted.
I cannot make any assumptions about the server (or clients) having a static IP or hostname (DNS can be broken anyways), nor can I make any assumptions about any existing PKI infrastructure.
I am writing this primarily in C#.Net, but would consider writing a C++ extension to this if it gives me this functionality.
Finally this is my first post here, so if I've missed out something obvious or have been short on any details, please ask and I'll fill in the gaps :)
Thanks,
James
In C# you can use PKIBlackbox package of our SecureBlackbox product which provides all the functionality you are looking for in .NET. Maybe BouncyCastle library also includes this functionality.
You need to rethink at least part of this. What you are doing is radically insecure. The client's private key needs to be generated at the client. Otherwise it isn't private, so it cannot possibly satisfy any of the tenets of PKI,. including the purpose for which you are issuing it. You lose uniqueness and you also lose non-repudiability. These are both fatal flaws.
Scenario:
A publically available Web Service that I have full control over.
But I only want this specific desktop application (my published application) to have access to the Web Service.
I could store a secret password in the desktop client, but that would be easy to crack.
Is there any known implementation that enforces this?
PKI, assymmetric keys?
If the public will have access to copies of this Desktop App, any good reverser will be able to crack it and "imitate" its transactions with the server. It doens't matter how secure is your cryptography, everything you app needs to encrypt/decrypt data is included in the binaries, so the cracker only needs to dig it out of it.
The objective of cryptography is to protect data while it is being transfered, from "middle-man" hackers, but if you have access to anyone of the peers, you can easily crack it.
Your server must never trust what comes from the client side.
[edit resuming]
Despite you cannot 100% guarantee a supposed client to your server is or isn't your App or some "emulator" made by thirdies, you can complicate things to them. Its a common practice in game anti-cheats to sometimes, randomly, make the client App a trick question like "whats the hash of your main.exe from offset A to offset B?" or "from now on packet type 0x07 swaps with packet type 0x5f". Once a fake is detected, server enter in a "silly mode", act malfunctional, and blacklist their IP/account to this mode for several hours so they cannot have sure of what their program is doing wrong.
If you detect someone is building an emulator, make them start all over again: jumble the packet type tables, cryptography tables, change some packet formats and force your clients to update. You won't see crackers bothering you for a while... LOL
WS-Security provides for X509 encryption.
Part of that implementation includes the possibility of only giving specific clients the generated public key. That way, only your selected clients can connect to the service.
The easiest way is message security using client and server certificates. The best way is to import the client certs in your server machines and hard code the client cert thumbprint in the app.config file. The other way is negotiation of certs which I haven't tried before.
If you are using IIS to host the service then client certificates using SSL is another option.
MSDN link on WCF Security.