iphone: is there any secure way to establish 2-way SSL from an application

Question

I need to establish a HTTPS 2-way SSL connection from my iPhone application to the customer's server. However I don't see any secure way to deliver the client side certificates to the application (it's an e-banking app, so security is really an issue). From what I have found so far the only way that the app would be able to access the certificate is to provide it pre-bundeled with the application itself, or expose an URL from which it could be fetched (IPhone app with SSL client certs).

The thing is that neither of this two ways prevent some third party to get the certificate, which if accepted as a risk eliminates the need for 2-way SSL (since anyone can have the client certificate).

The whole security protocol should look like this:
- HTTPS 2-way SSL to authenticate the application
- OTP (token) based user registration (client side key pair generated at this step)
- SOAP / WSS XML-Signature (requests signed by the keys generated earlier)

Any idea on how to establish the first layer of security (HTTPS) ?

Answer 1

Ok, so to answer my own question...

It turned out that the security has no fixed scale of measurement. The security requirements are satisfied as long as the price for braking the system is significantly above the prize that one would get for doing so.

In my situation we are talking about e-banking system, but with somewhat low monthly limits (couple of thousands USD). As I mentioned in my question there would be another layer of security above the HTTPS which will feature WSS XML-Signatures. The process of registering the user and accepting the his public key is also done in several steps. In the first step the user sends his telephone number together with a cod retrieved somehow from my client. Then an SMS is sent to the user with a confirmation code. The user enters the confirmation code into a OTP calculator that would produce OTP code which will identify the user. Then the public key is sent to the server together with the OTP code. From here on every request would be signed by the private counterpart of the public key sent to the server earlier.

So the biggest weakness for the whole process is that of someone reverse engineers the application and retrieves the client certificate used for the SLL. The only problem arising from this is that someone might observe users' transactions. However in order for someone to make a transaction he would need the user's private key, which is generated, encrypted and stored into the keychain. And the price for braking this security level is VERY HIGH.

We will additionally think on how to protect the users' data on a higher level (e.g. using WSS Encryption), but for the start I thing we are good with the current solution.

any opinion ?

regards

Answer 2

https doesn't really work this way. In a nutshell, you attach to a secure server where the certificates are signed by a well known authority.

If you use Apples (iPhone) classes for this, they will only accept 'good' certificates. By good, I mean what Apple deems as acceptable. If you don't use them (there are alternatives in the SDK), you won't be able to connect (except, maybe, in the case where you have an 'Enterprise' developers license - but I can't say that with 100% certainty as I haven't looked enough at this license to be sure)

To continue, use your https connection to your correctly signed website and then institute some sort of login with a built in username/password, or challenge/response based upon the unique ID of the iPhone (for example) and exchange keys using that connection.

Note that this means that your application will have to query for new certificates at (each connection/every X connections/every month/application specified intervals) to keep them up to date. You can then use these certificates to connect to the more secure server.

[edit]

Check this post - may have more information about what you're asking to do

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[edit2]

Please note that the request is iphone, not OSX - app store approval is an issue

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