A digital certificate is a digital document that certifies that a certain public key is owned by a particular user. Thus if you trust the CA that signed the certificate C, then you can trust that specific public/private key pair is owned by the owner of certificate C.
a) Assume client A wants to establish a connection with server B located at url www.some_domain.com. When establishing a connection with B, A may receive from the other end a X.509 certificate C and a public key, belonging to the owner of certificate C.
But how can client know that owner of C is really a server B and not some other entity that hijacked ( if that is the correct term ) the connection and sent its own certificate and public key to A?
Only way I can think of for client to know whether owner of C is really B, is if C's Subject field also specifies the domain for which this certificate is valid or if it specifies the organization to which this certificate belongs ( but that only helps if client knows to which organization www.some_domain.com belongs )?!
thank you
All a certificate can do is ensure that the communications between A and C are encrypted such that C (or whatever has the certificate installed) is the only one able to decrypt it.
It makes absolutely no representation with regards to who C is owned by. Some Certificate Authorities will try and establish that a given entity is who they say they are prior to disbursing a certificate. However, quite frankly, all of that can be duped and most sites don't bother paying for that level of research anyway (called Extended Validation).
Now, if some crook has stolen the certificate from server C and set up their own server (with the same fully qualified domain name), then yes they can impersonate away. However, this would require an additional step of poisoning DNS resolution so that requests to www.some_domain.com go to the hacker's server and not the original. It's usually much easier just to crack the original server and install your own data capture software.
As a side note there are huge security issues with DNS resolution.
Another note, recently the stuxnet worm used a stolen code signing certificate to get past some of the windows installation protections.
Because 'C' is signed by a CA certificate authority that is already on your system. That is why the scheme can be broken by governments that control the CA's.
If you look at a certificate in your browser then you can see who signed it. For instance gmail is signed by Thawte which is signed by Verisign. The CN field is marked www.google.com so it will only be valid for that domain.
Maybe you are talking about man in the middle:
http://en.wikipedia.org/wiki/Man-in-the-middle_attack
A man-in-the-middle attack can succeed only when the attacker can impersonate each endpoint to the satisfaction of the other—it is an attack on mutual authentication. Most cryptographic protocols include some form of endpoint authentication specifically to prevent MITM attacks. For example, SSL authenticates the server using a mutually trusted certification authority.
So in your scenario only one side would be fooled. Check out step 2 below:
https://ssl.trustwave.com/support/support-how-ssl-works.php
Step 1: A customer makes a connection to xyz.com on an SSL port, typically 443. This connection is denoted with https instead of http.
Step 2: xyz.com sends back its public key to the customer. Once customer receives it, his/her browser decides if it is alright to proceed.
The xyz.com public key must NOT be expired
The xyz.com public key must be for xyz.com only
The client must have the public key for Trustwave installed in their browser certificate store. 99.9% of all modern browsers (1998+) include the Trustwave root certificate. If the customer has Trustwave trusted public key, then they can trust that they are really communicating with XYZ, Inc.
Step 3: If the customer decides to trust the certificate, then the customer will be sent to xyz.com his/her public key.
-Step 4: xyz.com will next create a unique hash and encrypt it using both the customer's public key and xyz.com's private key, and send this back to the client.
Step 5: Customer's browser will decrypt the hash. This process shows that the xyz.com sent the hash and only the customer is able to read it.
Step 6: Customer and website can now securely exchange information.
A is typically configured with a set of trusted CAs, which map C's public key to trusted entities, in this case B. Did you not answer your own question in the first paragraph, or am I missing something?
So the client A needs to know if certificate C is genuine. Whose task is to verify this?
Ans: A's browser.
How will it verify?
Ans: Browser checks who signed the certificate.
Who signed the certificate?
Ans: A C.A(Certification Authority) named AweCerts.Inc
Does the browser know this CA. And does the broswer trust CA?
Ans: Yes. If the broswer does not trust then A cannot proceed further. And not only does the broswer trust AweCerts but her/his friends as well (the whole chain that is).
How does the browser know this certificate was signed by AweCerts.Inc?
Ans: Browser had an agreement with AweCerts. Microsoft does this in IE's case.
If the browser is able to unlock the message(outer covering) with AweCerts public key then it is sure that it was 'encrypted with AweCerts private key' or signed by Awecerts.
We usually encrypt with public keys and have it decrypted with private keys. But the other way around is possible as well and that is infact what we call Digital Signature. And you can check my blog for more interesting info on certificates and messaging.
There is an interesting blog here http://the-blueclouds.blogspot.nl/2011/11/public-key-private-key-hashing-blah.html
Related
Some time ago I've worked on setting up SSO user authentication in a web application. The specific IdP was an ADFS server, but I don't think that's very important.
When configuring the application's SSO settings, I noticed that the IdP certificate's fingerprint is required, but not the certificate itself. Now, as I understand, the fingerprint is used by the application to validate the IdP's signature on the issued SAML token.
The question is how can the application verify the signature with just the certificate fingerprint? Doesn't it need the certificate's public key, which is part of the certificate itself, but not of it's fingerprint? How does this signature verification process work?
The fingerprint is exchanged out-of-band between the sender and the receiver and is configured on the receiving end. It uniquely identifies a certificate with the public key that the sender uses to sign the SAML messages that it sends.
The certificate itself can then be sent in-band as part of the SAML message itself. The receiver will compare the fingerprint of that certificate against the stored fingerprint to confirm that is dealing with the appropriate sender and associated key before cryptographically verifying the SAML message with that key.
This has the advantage that only a small message needs to be exchanged out-of-band beforehand. This may be useful e.g. when read out over a telephone line but has the downside that the complete certificate needs to be sent with each message (well, in principle at least the first message...) which increases the size of each message.
I'm consuming a soap service from a server that uses ssl certificate. Although I don't have any dependency on the server certificate in my code, but what if the server certificate gets expired? Will the communication between the server and my client be OK?
In general: no, the communication will not be OK.
A certificate is an endorsement, by the issuer, that the requester has met the identity (and other) requirements that the issuer has put in place; and that the public key in the certificate really is associated with the subject.
The expiration date for the certificate exists because the longer ago the verification process was, the more likely it won't hold up anymore. Imagine you bought awesomesauce.example.com, and got a TLS server certificate for it, and the cert had no expiration. After a year you forget to pay your registrar and lose the name. Someone else comes along, buys it, and has a popular website there. You realize that you have a certificate that identifies you as that site, so you sell it for a million BTC to some hacker group who uses it to do various identity theft tricks and ...
This is similar to an expiration on a driver's license. Maybe your eyesight has dropped below the acceptable thresholds and you shouldn't drive. Maybe you moved and the address on the card should no longer be trusted. Slap an expiration date on there and you now have to reaffirm the facts therein.
You can get an idea of how your client will handle expiration by making a request to https://expired.badssl.com/. If it works, you're trusting outdated claims. If it doesn't: be happy about your client doing the right thing.
Ok I'm sure this is obvious and I am missing something very fundamental here. We are sending an http request to a server. To prove it is us who is sending the request, we attach a certificate to it.
This certificate has a trusted CA, so the server knows that the certificate is genuine.
The bit I don't get is that we say to the server, ok trust certificates from Comodo let's say. Fine. So I send the request, it says I am 'Company A' and this is certified by Comodo.
Our clients who run the server just want to know who the CA is so they can trust it. Makes sense. But surely something else in the certificate needs checking to like the embedded company name? Otherwise I could go buy another certificate for my own personal company say, and get it from Comodo and that certificate would be valid according to the server too.
Please enlighten me!
Thanks
Simon
If I understand correctly, you're asking how a person at a web browser going to a web site for 'Company A' can be sure that it really is 'Company A' and not an imposter with a certificate from 'Company B' issued by the same trusted CA (Comodo).
The quick answer is that the browser does check the name on the certificate, not just whether it trusts the issuing CA. The Subject field in a certificate is a Distinguished Name (DN) that looks something like this:
CN = www.google.com, O = Google Inc, L = Mountain View, S = California, C = US
The browser can check that the CN (Canonical Name) matches what you entered in your browser (https://www.google.com/) to be sure that you're at the right site. Sometimes the CN does not match, but the certificate includes Subject Alternative Names that include a name that does match. In either case the certificate includes the web site that you are attempting to load, so you can validate that it is the correct certificate for that site.
In addition there are many other checks that are (or could be) done:
* Check that current date and time is within the validity period for the certificate
* Check that the certificate is not revoked (using CRL or OCSP)
* Check that the signature is valid and signed by a trusted CA
* Check that the signing CA is actually a CA (Key Usage field in CA's certificate)
* Check the usage of the certificate itself to be sure it is a server certificate
* Check that the public key is strong enough (e.g., at least 2048 bit RSA)
* Check that the signature algorithm is strong enough (e.g., SHA256RSA vs. SHA1RSA)
* Check that the validity period is short enough (e.g., 3 years or less for servers)
I have set up a single sign on(SSO) for my services. All the services confirm the identity of the user using the IDPorvider(IDP). In my case I am also the IDP.
In my saml request, I have included the following:
1. the level for which auth. is required.
2. the consumer url
3. the destination service url.
4. Issuer
Then, encrypting this message with the SP's(service provider) private key and then with the IDP's Public key. Then I am sending this request.
The IDP on receiving the request, first decrypts with his own private key and then with SP's public key. In the saml response:
1. destination url
2. Issuer
3. Status of the response
Is this good enough? Please give your suggestions?
In general it goes something like this. There is encryption and then there is singing in SAML. You never want to be in production without digital signature sbeing used for SAML. You can disable signature processing for testing purposes I suppose. We alow this in SiteMinder Federation Servcies (SMFSS) for testing purposes only. So, with that being said you're not saying anything about digital signatures and are only talking about encryption.
But here is a rundown of the two in my own very dumbed down description which although I sound silly with the way I explain it I am hoping it will help you. And if you already know this I apologize in advance. One more thing is that this is very basic but you can get more details on google searching for encrytpion, decryption, certificates, etc.
Actually, here is a rundown of what I use to train new support folks for Federation with SMFSS (SiteMinder Federation Services) and at the end is the section I wrote on certs. This was just something I wrote up very quickly and is not very slick looking but it defintiely gets the job done, and quickly. It was written as sort of a copy of what I do with POC SAML 2.0 POST customers who already have SiteMinder setup. I just figured I would give you this since it has a lot of tools you may find useful once you get going in case you were not aware of them already. ;-)
You will need two environments with Agent, Agent OP, Policy Server, Policy Server OP. Need two agents so one can be IDP and one SP.
To set up Agent Option Pack see:
Chapter 8: Federation Web Services Application Setup & Deploy Federation Web Services as a Web Application & Configure ServletExec to Work with Federation Web Services
Now set up the SAML 2.0 POST authentication: You should use the following as it is step by step. But first see the chapter on settings that must match as they need to match for the IDP and SP sides. The chapters below for IDP and SP set up are pretty much step by step, really, Follow 14 and 16 step by step and you’re good to go.
Chapter 22: Configuration Settings that Must Use the Same Values
Then use this to set up the IDP and SP:
Chapter 14: Configure SiteMinder as a SAML 2.0 Identity Provider
Chapter 16: Configure SiteMinder as a SAML 2.0 Service Provider
Run your SAML 2.0 transaction and get a Fiddler Trace of it. Pull out the certs and create a .cer file. Pull out the assertion and check the XML online using the tools below.
Set up Fiddler Tool and make sure you have HTTPS Decryption enabled. I had the link here but just go to gllgle and type in "Fiddler Tool HTTPS decryption" and you'll get it.
Used to review the URL posted or redirected with SAML transactions taken out of Fiddler Usually:
https://rnd.feide.no/simplesaml/module.php/saml2debug/debug.php
I have used this one multiple times to validate XML (the assertion) when I get parsing errors or other errors with partners saying our assertion is not good or if we have a partners assertion that is not good. I like to check the syntax first and if that is fine then check SAML specs to see if they have correct values in the SAML assertion itself. In other words make sure it is SAML compliant.
http://www.w3schools.com/dom/dom_validate.asp
HINT: You can take the base 64 encoded cert info out of our logs or the Fiddler Traces and paste to a notepad and save it as name.cer. Then when you open this file you can look at the cert the customer is using. This is helpful because then you can see if they have the right cert and see who their Root CA is or their intermediate Root CA. Make sure you get all the data including the = or == that may be at the end of the lines for the cert info.
When performing SLO or Artifact the partner will need to connect on the back channel to a web server on the other partners site. When this happens the Web Server being connected to is being served over SSL/HTTPS. This means that the one connecting to that server must have the ROOT CA cert which signed the web sever’s cert in it’s keystore. The theory of this is the same as when you open a browser and connect to an HTTPS web server. All browsers come with the major Root CA certs already imported into them. The whole point of this is that when you put a cert on a web server it is not really for protection it is to let anyone who connects know that you really are that website and really are who you say you are. The fact that you have a cert makes your site be HTTPS and the reason you believe they are who they say they are is that they give you their cert when you connect and if you have the ROOT CA for that cert on the website then this means you trust their ROOT CA. if you trust their ROOT CA then you can connect. If you do not have the ROOT CA cert imported into your browser then you can not connect over SSL/HTTPS to that webserver.
**Encryption and Decryption (if a packet is reads off the wire then the data is encrypted for safety of packet data):
Encryption is done on the IDP side and you can encrypt the entire assertion, NameID value, Attributes and perhaps more?
Encryption is done on the IDP side using the PUBLIC Key Certificate (SP’s cert) which is given to the IDP offline by the SP.
When the SP gets the assertion (or whatever the IDP encrypted) then it must have it’s private key in it’s keystore so that it can decrypt the data and read it. This is the decryption.
The reason this is secure and protects the data is that ONLY the SP should have their own PRIVATE key. Thus if this packet was stolen no one can decrypt it but them.
***Signing and verification – This is not SECURE as it does not encrypt the data. It is not meant to be secure for the packets it is meant to tell someone you really are who you say you are. So if you sign and assertion your partner will know it came from the IDP they expected it to come from.
The IDP must use their public/private key PAIR to sign the data.
The SP must use the IDP’s PUBLIC key (given to the SP offline) to verify the signature. The reason you know the data is from that IDP is that ONLY data signed with the IDP’s private key and be decrypted with their public key. In other words, you can’t pretend you are that IDP and send signed data to the SP and get them to think it is the IDP because the public key for the IDP can only be used to verify things signed with the matching private key. This proves you are who you say you are.
end silly technote I wrote**
I hope you find the certs info and tools useful in your future SAML endeavours! Happy Federating!
update - I was not able to post all the links but some were just base 64 decryption as it will allow me to post only two I am posting the most needed two.
Thanks!
Crissy Stone
CA Technologies SiteMinder Support
I'm building a solution consisting of an app and a server. Server provides some methods (json) and the app uses them. My aim is to make those API methods inaccessible to other clients. What is the best way to do so?
Should I take a look at certificates (to sign every outgoing request)? If yes, where do I start and what is the performance impact of doing so?
What are alternatives?
Put another way, you need a way to distinguish a valid client's request from an invalid client's request. That means the client needs to present credentials that demonstrate the request comes from a valid source.
SSL certificates are an excellent way to assert identity that can be validated. The validity of an SSL certificate can be confirmed if the certificate contains a valid signature created by another certificate known to be secure, a root cert. As noted in other answers an embedded certificate won't do the job because that certificate can be compromised by dissecting the app. Once it is compromised, you can't accept any requests presenting it, locking out all your users.
Instead of one embedded app cert, you need to issue a separate certificate to each valid user. To do that, you need to set up (or outsource to) a Certificate Authority and issue individual, signed certificates to valid clients. Some of these certificate will be compromised by the user -- either because they were hacked, careless or intentionally trying to defraud your service. You'll need to watch for these stolen certificates, place them on a certificate revocation list (CRL) and refuse service to these compromised certificates. Any web server is able to refuse a connection based on a CRL.
This doesn't solve the security issues, it just moves them out of the app. It is still possible for someone to create what appears to be a valid certificate through social engineering or by stealing your root certificate and manufacturing new signed certificates. (These are problems all PKI providers face.)
There will be a performance hit. How much of a hit depends on the number of requests from the app. The iPhone NSURLConnection class provides support for SSL client certificates and client certificates can be installed in the phone from an e-mail or authenticated web request. Managing the infrastructure to support the client certs will require more effort than coding it into the app.
Incidentally, voting down any answer you don't like creates a chilling effect in the community. You're not nearly as likely to get advice -- good or bad -- if you're going to take a whack at everyone's reputation score.
I will now freely admit that it's an interesting question, but I have no idea how it could be done.
Original answer:
Interesting question. Assuming people can't reverse-engineer the iPhone app, the only solution that comes to mind would be to sign requests with a public key, or some other secret known only to the application. By that, I mean adding an extra argument to every API call that is a hash of the destination URL and other arguments combined with a secret known only to your server and application.
To expand upon this: suppose your API call has arguments foo, bar and qux. I would add a signature argument, the value of which could be something as simple as sorting the other arguments by name, concatenating them with their values, adding a secret, and hashing the lot. Then on the server side, I would do the same thing (excepting the signature argument) and check that the hash matches the one we were given in the request.
Consider authenticated HTTP.
For a cheaper alternative, there's shared secret/hash scheme. The client and the server have a shared secret string of text. Upon request, the client hashes together (using MD5, or SHA1, or SHA something else - you choose) the request fields and the secret. The hash value is attached to the request - say, as another POST field.
The server does the same operation with the request and with its copy of the secret, then compares the hash values. If they don't match - service denied.
For added security, you may encrypt the hash with a RSA public key. The client has the public key, the server keeps the private key. The server decrypts the hash with the private key, then the same. I did that with a C++ WinMobile client and a PHP-based service - works like a charm. No experience with crypto on iPhone, though.
UPDATE: now that I think of it, if we assume that the attacker has complete control over the client (ahem jailbroken iPhone and a debugger), the problem, as formulated above, is not solvable in theory. After all, the attacker might use your bits to access the service. Reverse-engineer the executable, find the relevant functions and call them with desired data. Build some global state, if necessary. Alternatively, they can automate your UI, screen scraper style. Such is the sad state of affairs.