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How are ssl certificates verified?
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Closed 1 year ago.
I have one doubt regarding process of server SSL certificate's verification by the web browser (like Firefox/Chrome).
I read a lot about mechanisms which minimize the risk of application of misissued CA/intermediate CA certificates (i.e. hacked CA or mistakenly issued certificates to entities who actually shouldn't receive them) by attackers/hackers, such as HPKP HTTP header or Certificate Transparency Log.
According to explanations I read, pottential attacker could present this wrongly issued certificate to impersonate end server and hijack content from a request sender which is expected to be encrypted.
But how is it possible? What is the mechanism of verification of certificate by the browser?
When I used programming libraries to execeute requests to APIs over HTTPS, there was an option turned on by default to compare "Subject" field in the certificate with the URL I passed to query the service. If comparison failed, communication has been broken. This setting can be bypassed (in Apache HTTP it is called NoopHostnameVerifier). If I understand well, this functionality causes, that if i posess domain for example "blablabla.com" and present misissued certificate for the domaind "xyxyxy.xom" with valid signature of the CA, Http Client will block the connection due to the mismatch of Subject in certificate with requested URL.
How it works in browsers? Does the browser do the comparison between Subject in x509 certificate and URL in address bar? If no, why browsers don't do this comparison? If yes, do the browsers block this request? or just render some warning?
In other words: is correctly verified signature of the CA the only condition to acknowledge certificate and whole server's response with certificate as valid ? mismatch between "Subject" field in X509 and URL address bar is neglected by the browser in this case?
Browsers do a very extensive check before accepting server certificate, including chain validation, name comparison, etc. Here is a relevant thread which answers your question: https://security.stackexchange.com/questions/56389/ssl-certificate-framework-101-how-does-the-browser-actually-verify-the-validity
Related
I have some code that uses Exchangelib to process emails. For various reasons, the certificate validation fails and I have to use the usual NoVerifyHTTPAdapter:
from exchangelib.protocol import BaseProtocol, NoVerifyHTTPAdapter
# Tell exchangelib to use this adapter class instead of the default
BaseProtocol.HTTP_ADAPTER_CLS = NoVerifyHTTPAdapter
This leads me to two questions:
I am now wondering, am I sending and receiving in plain text without encryption? I know that the servers I am using only have port 443 open.
If I am not sending in plain text, is there a way to get the name of the certificate that I am using?
If this question is answered somewhere else, sorry for the inconvenience, it must have slipped in my initial search.
You are not sending in plain text. Your data is still encrypted since you are communicating over HTTPS.
When certificate validation fails, it means that the certificate of the server cannot be validated using any of the root certificates on your local machine that you (or your OS vendor) have chosen to trust, or that the certificate does not match the server that you are communicating with, that the certificate has expired, or any of the other reasons that may cause failure to validate a certificate.
This means that you have no guarantee that the server you are communicating with is in fact the correct server, which leaves you vulnerable to man-in-the-middle attacks and exposing your data to an untrusted server. But the communication channel itself is still encrypted.
There's some more discussion at What are the implications of ignoring SSL certificate verification?
If you absolutely cannot fix the causes of the invalid certificate, your best option is to accept the certificate locally: How to get Python requests to trust a self signed SSL certificate?
I was trying to get myself familiarised with basic concepts of https when I came across its encryption, which in a nutshell functions as follows,
Now I have seen QA engineers in my company use this tool called burp-suite to intercept request.
What I am confused about is even though the data flows through an encrypted channel, how can any interception tool like burp-suite manage to intercept the request.
Just to try it out I tried to intercept facebook request in burp-suite,
Here you can clearly see the test email test#gmail.com I used in the intercepted request.
Why is this data not encrypted according to https standards?
Or if it is then how do burp-suite manage to decrypt it?
Thank you.
Meta: this isn't really a development or programming question or problem, although Burp is sometimes used for research or debugging.
If you LOOK AT THE DOCUMENTATION on Using Burp Proxy
Burp CA certificate - Since Burp breaks TLS connections between your browser and servers, your browser will by default show a warning message if you visit an HTTPS site via Burp Proxy. This is because the browser does not recognize Burp's TLS certificate, and infers that your traffic may be being intercepted by a third-party attacker. To use Burp effectively with TLS connections, you really need to install Burp's Certificate Authority master certificate in your browser, so that it trusts the certificates generated by Burp.
and following the link provided right there
By default, when you browse an HTTPS website via Burp, the Proxy generates a TLS certificate for each host, signed by its own Certificate Authority (CA) certificate. ...
Using its own generated cert (and matching key, although the webpage doesn't talk about that because it isn't visible to people) instead of the cert from the real site allows Burp to 'terminate' the TLS session from the client, decrypting and examining the data, and then forwarding that data over a different TLS session to the real site, and vice versa on the response (unless configured to do something different like modify the data).
... This CA certificate is generated the first time Burp is run, and stored locally. To use Burp Proxy most effectively with HTTPS websites, you will need to install Burp's CA certificate as a trusted root in your browser.
This is followed by a warning about the risks, and a link to instructions to do so.
Having its own CA cert trusted in the browser means that the generated cert is accepted by the browser and everything looks mostly normal to the browser user (or other client).
I am developing browser extension, that sends some data from currently browsed page to my backend server. User is aware of it, it is intended.
I don't want to cause any user-data exposure, when the user is e.g. on unsecured wifi. So I just want to ensure, the data and the url goes over the net encrypted and only my backend will see them.
Do I understand correctly, that any SSL certificate, even free one from StartSSL will do the trick?
What other side effects with free SSL certificate should I consider?
- will the user's http-client trust such a certificate?
Thanks.
The SSL certificate will do the trick as long as it can be validated. That means that the root certificate of the certificate chain needs to be within the trusted certificate store of the browser.
Furthermore, the certificate will have to be for the right address (URL), must not be revoked, CRL's and OCSP must be configured correctly etc. etc. In other words, the usual steps required to have your web-service certificate validated must be met.
I need to implement a SSL certificate for a website, I've got three questions after some research.
1) I believe i need to buy a SSL certificate and ask my host to install it. My question is do you need to alter any code for the website for the certificate?
2) Before I buy the certificate, the website is going to be built for a couple of month at least. I'm just wondering is there a developing SSL certificate I can use for the developing environment?
3) Or do I have to use self assigned certificate? If so are there any good tutorials on how to create a SSL self assigned certificate on a local machine (wamp) and a developing url site?
Thank you very much.
Sam :)
1) No, you do not need to alter any code on your website at all in order to use an installed SSL certificate. It is as simple as prefixing your desired destination link with the HTTPS: protocol specification instead of the typical HTTP: protocol. However, if you want to determine if your site visitor is using an encrypted page before they do something, such as submit a web form with potentially sensitive data, then depending on what you are developing your site in, you will need to detect if the current page request has been sent over HTTP or HTTPS, then if it is an HTTP requested page, you probably want to redirect the page request to the HTTPS version before proceeding.
2) Other than creating your own "self signed" certificate (more on this in #3), no your only option for a publicly valid SSL certificate is to obtain one from a publicly recognized Certificate Authority (CA). Long story short, a certificate of the same key length using the same encryption standard supported by your server and visitor's web browser, is no stronger or weaker regardless of vendor for purposes of encryption. So you can simply shop by price for your SSL certs. I have no affiliation with GoDaddy, but have been using them for years for public SSL certificates.
3) You certainly can create your own self signed certificate. The methods for doing this vary based on your host server and version. The limitation to a self signed certificate, is that if you go to share this with anyone, you get that warning message from your browser that the certificate is not published from a verifiable source. In most current browsers, it looks like a big scary message that something is wrong and they attempt to warn your user away from doing this. However, of course, there is certainly nothing wrong with using a self signed certificate. This is obviously true for your own development uses. Even a self signed certificate of the same key length and encryption method is as cryptographically secure as a commercially provided certificate. If you want to use a self signed certificate, just search for instruction for doing that for your server OS and version for details. Once it is installed, you will get the warning from your browser when you try to browse to a page over HTTPS. Your browser should show you an option to permanently remember and accept your self signed certificate, after which you will no longer see that warning while that certificate remains installed and valid.
We are looking for guidelines for testing a new product that works as a "man in the middle" proxy, and intercept HTTPS traffic.
This system needs to act as a standard browsers and block any attempt to access a site with invalid certificate.
We thought about testing the following scenarios:
Expired certificate
A certificate that was issues for a future date
The requested hostname does not match the certificate hostname
The certificate is not signed by a root CA
My questions are:
What other certificates scenario should we test?
Which tools should we use to generate those "invalid" certificates?
Do you know of any open source project (maybe a browser or proxy) that has a set of unit tests that we can learn from?
Thanks.
The procedure of certificate validation is completely described in the corresponding RFCs (3280, 2560 etc.) and you don't need to invent any "scenarios".
For generation of certificates including invalid ones you can use our SecureBlackbox components (trial mode will be enough).