I want to understand what self signed certificate means.
any explanation is appreciated.
Self Signed Certificates are types of SSL certificates that are generated by an independent person (such as yourself), rather than generated by a Certificate Authority.
Many organizations are tempted to use self-signed SSL Certificates instead of those issued and verified by a trusted Certificate Authority mainly because of the price difference. Unlike CA issued certificates, self-signed certificates are free of charge. What most users are not aware of is that self-signed certificates can end up costing them more in the long run.
While self-signed SSL Certificates also encrypt customers' log in and other personal account credentials, they prompt most web servers to display a security alert because the certificate was not verified by a trusted Certificate Authority. Often the alerts advise the visitor to abort browsing the page for security reasons.
In cryptography and computer security, a self-signed certificate is an identity certificate that is signed by the same entity whose identity it certifies. This term has nothing to do with the identity of the person or organization that actually performed the signing procedure.
It means that the people who are providing the certificate are the same people the certificate is being issued to, usually done this way because it is free.
It is best to have a certificate provided by a trusted Certificate Authority however, It will cost money, but is more trustworthy.
Related
I have some secrets that I would like to keep in Azure Key Vault. I know I can use a client id and certificate to authenticate with Key Vault instead of using a client and and secret following these steps:
Get or Create a Certificate
Associate the Certificate with an Azure AD application
Add code to your application to use the Certificate
Most examples use either makecert or New-SelfSignedCertificate to create the certificate. Is a self signed certificate problematic in this case for a production application? This is only for an application to authenticate with Azure Key Vault and it's not something a client will ever see in their browser.
If a self signed cert is still frowned upon in this case then is purchasing a cert from a trusted authority the same process as purchasing an SSL/TLS certificate? Is it even the same type of certificate?
There is (with some caveats) nothing inherently wrong with using a self-signed certificate. There is no difference from a pure crypto perspective between a purchased and a self-signed certificate. The sole difference is that a purchased certificate has been signed by one or more certificate authorities (CAs) who distribute their public keys with most browsers/operating systems/etc. This means that a user can have a much higher confidence that a purchased certificate is legitimate, while they must take a leap of faith to accept a self-signed certificate.
In your case, however, you seem to be able to control the client application, and actual users should never see this certificate. Therefore, you can use a self-signed certificate without worry, so long as you take precautions to prevent man-in-the-middle attacks (i.e. someone generating their own self-signed certificate and pretending to be you.). One of the most effective ways to do this is via certificate pinning. In essence, you ship the public key for your certificate with you client application, and your client application will only accept certificates that provide that public key. This makes it much more difficult for a malicious actor (who has not stolen your certificate) to preform a man-in-the-middle attack.
TL;DR: So long as you take steps to prevent man-in-the-middle attacks, and you keep your certificate secure, there is nothing wrong with using a self-signed and self-generated certificate to secure non-user-facing connections.
How does the client ensure the ssl certificate that the server send is the true owner of the certificate? How does it prevent a hacker from cloning, for example, the google ssl certificate, and trick me that he is the google site during the handshaking? can the hacker clone the certificate and modify the domain or ip info from network packet to trick people?
An SSL certificate for e.g. www.google.com is signed by a 3rd party named a Certificate Authority (CA). In the case of google that 3rd party is currently "GeoTrust Global CA". Too look up who it is, you need to inspect the certificate (browsers typically will let you do that rather easily, but each has their own way)
That links the certificate with the name "www.google.com".
Your client(s) have a list of CAs they trust on your behalf. That list is either maintained by the vendor of your OS and/or by the creator of your client/browser.
So how does the client know it's talking to the right server ?
The certificate is signed by a CA it trusts, the certificate is for the name the client wants to connect to, and the server delivered proof it knows the corresponding secret key to the public key that's in the certificate.
A hacker who would copy a valid certificate from www.google.com and place it on their own machine would only have the public key and not have the private key.
A hacker who would try to get their certificate request signed by a reputable CA would get rejected because they cannot proof to own the google.com domain. And hence the name would not match.
A hacker who would sign their own certificate request, would fail as their self-built CA is not in the trusted list.
A hacker who would break into google's servers and copy the secret key somehow, could pass muster for a while, but once the folks at Google detect it, they would contact their CA and revoke the certificate.
Now this process is the weak point in most implementations as these revoked certificates are published by the CA as Certificate Revocation Lists (CRLs) or as an OCSP (Online Certificate Status Protocol) service, but clients typically take the shortcut and do not validate that a certificate has not been revoked.
We can create our own Certificate Authority and issue a certificate to our server. But the browsers doesn't recognize it as a trusted one. Yes we can configure our browsers to trust our certificate. But how can we make our certificate as a universally trusted one like VeriSign or other trusted certificates?
The only way is to obtain a trusted certificate from a Certificate Authority (CA) due to the necessity of a Trust Chain.
There are several free sources like:
https://www.startssl.com/
Also, starting Fall 2015 there will be a free service to obtain trusted certs from
Let's Encrypt.
https://letsencrypt.org/
Let’s Encrypt is a free, automated, and open certificate authority
brought to you by the Internet Security Research Group (ISRG),
including the Electronic Frontier Foundation, Mozilla, Cisco, and Akamai.
I've read about SSL protocol and now, I know how it encrypts data. But there is something I couldn't understand. With SSL , you're sure you're sending data to and getting data from correct server. But how?
I mean if I create a fake certificate and send it for requests of special website, how do browsers ( or other programs) detect the fake certificate?
Edit: I didn't mean to create a self-signed certificate. I meant how can someone validate my certificate if I create a certificate that its issuer and subject ,etc are something to real certificate! (the only things that are not real is Public key & signature)
TL;DR summary:
Validity of a server certificate is established by:
Host name verification
Verifying the signatures of the entire certificate chain
Performing additional checks on meta data for each certificate
Checking the revocation status of each of the certificates involved
Checking whether the self-signed root certificate of the chain is among the certificates that one trusts by default
Explanation
Let's assume you want to connect to https://mail.google.com (you can try this out in your browser!).
The (real) server will respond with a certificate that is issued to mail.google.com, i.e. in the 'Subject' field of the certificate you will find the Common Name (CN) 'mail.google.com' - cf. RFC 5280 for details on the fields of certificates. The fact that the subject is linked to the site URL is very important for the security of the whole model, and it is actively checked by your TLS implementation ("host name verification"), because otherwise there would be room for Man-In-The-Middle attacks. I.e. somebody could acquire an otherwise valid certificate and impersonate mail.google.com without you taking any notice of it.
In addition to the host name verification, your TLS implementation will also check the "validity" of the certificate. The whole procedure is rather complex and does include checking the trustworthiness of the certificate, but additionally a lot of other things will be checked, more on that in a minute.
If you view Google Mail's certificate in your browser, you will notice that there are actually three certificates shown:
mail.google.com
Thawte SGC CA
Class 3 Public Primary Certification Authority (VeriSign)
The model is that there are a few (well, unfortunately not so few anymore) trusted root certificate authorities ("root CAs") that either you could choose on your own or (more likely) that come preconfigued with your software (e.g. browser) that are blindly trusted. These trusted authorities form the anchors of the entire trust model of "PKI" (Public Key Infrastructure). The basic idea is that the trusted entities may issue certificates to other authorities and grant them permission to again issue certificates (these authorities are called intermediate certificate authorities). The intermediate CAs may again recursively apply this procedure up to a certain point, the number of intermediate CAs between an actual end entity certificate and a root CA certificate is generally limited.
At one point, an intermediate CA will issue certificates to an "end entity" ("mail.google.com" in our example). Now the process of issuing a certificate actually means that the party requesting a certificate will create a public/private key pair first, and use them to authenticate a certificate request that is sent to the certificate authority. The issuing authority creates a certificate for the subordinate entity (either intermediate CA or end entity) by "signing" that certificate using its own private key using an asymmetric algorithm such as RSA and by additionally including the public key of the requesting party within the newly generated certificate. The root CA possesses a so called self-signed certificate, i.e. the root CA is the only authority that may sign their own certificate and include their own public key. The private key remains hidden at all times, of course.
The recursive nature of the certificate issuing process implies that for each end entity certificate there is a unique way of establishing a "chain" of certificates that leads up to a root certificate authority. Now when you are presented with an end entity certificate while trying to connect to a TLS-secured site, the following procedure will be applied recursively until you end up with a root CA certificate:
Find the certificate of the authority that issued the certificate to be validated (see RFC 5280 for details). If none is found: exit with error.
Take the public key of the issuing certificate and verify the signature of the to-be-validated certificate using this public key.
Check a lot of additional things such as whether the certificate has neither expired nor is it not valid yet, "policy constraints", "key usages", "extended key usages"... (again, the gory details are in the RFC).
Certificate revocation status (more on that later)
If all checks were positive, you will ultimately end up with a certificate being self-signed, i.e. where the subject is also the issuer (such as the VeriSign certificate in our example). Now the last thing you have to verify is whether this certificate is among those that you blindly trust: if it is, all is well and the connection will succeed, if it is not, the connection attempt will be rejected.
As if this were not complicated enough already, the checks described so far do not handle cases where once valid certificates suddenly become rogue, examples being cases where a certificate is stolen or private keys are compromised (think of Comodo and DigiNotar). In these cases, the normal procedure is to "revoke" those certificates gone bad, that is you want to mark them as being invalid starting from a distinct point in time (they will expire at some point anyway, but for the remainder of that period they shall already be marked as invalid). For these cases, CAs have the possibility to issue CRLs (a catalog of certificates declared as invalid) or OCSP responses (information for one or in rare cases a set of certificates) that provides clients with information whether a given certificate has been marked as invalid or not. The revocation status needs to be checked for all certificates in a chain, should one of them be marked as invalid then the end entity certificate cannot be trusted and the connection must be rejected as well.
SSL certificates are signed by a certificate authority (CA), which is someone the user already trusts (or more likely, the people who designed their operating system trusts).
The CA digitally signs the certificate using public key encryption. The basic explanation is that the CA has a "private key", and a "public key" that everyone knows. Via some math I don't understand, the CA can create a signature using its private key which can easily be verified with its public key (but the public key can't be used to create a new signature).
When you get an SSL certificate from a server, you get the server's public key, and a signature from a CA saying that it's valid (along with some other info). If you know and trust that CA, you can check the signature and determine if it's valid. You can also use a certificate revocation list to make sure it wasn't revoked.
So basically, you can recognize a bad SSL certificate because it isn't signed by a certificate authority that you trust.
Any fake certificate you create will be a self-signed certificate.
The browser will display big scary warnings when connecting to a site with a self-signed certificate which the user will promptly ignore.
In order to avoid warnings, you need a certificate signed by a certificate authority that the browser trusts, such as VeriSign.
These companies will hopefully make sure that you actually own the domain for the certificate they're signing.
Re: Edit: You can only create a non-self-signed certificate if you get it signed from a trusted CA.
They will refuse to sign a certificate for a different subject.
Process from my understanding:
server sends servers public key
server sends certificate (all information encrypted by trusted CA with their private key)
Your PC decrypts certificate with public key (built into OS from trusted CA)
Your PC hashes (with sha1 and sha256) the servers public key
Your PC compares the hashes of servers public key with certificate stored hash, if not same browser will block site
Your PC compares allowed domains from certificate and the domain, if not allowed, if not same browser will block site
Your PC compares valid date from certificate and your date, if not valid browser will block site.
To fake this you would either need to:
obtain a CA private key (extremely hard to get),
be a CA,
be part of the 5 eyes (Government intelligence agency alliance) and ask a CA for their private key
So if you see a padlock in the address bar you are almost always safe.
Certificates work because they follow a chain of trust. Certificates have a chain of one or more issuers that are trusted; this chain is the backbone of why it works at all. Browsers and nearly all SSL certificate libraries do this chain check, or at least provide the option to.
Self-signed certificates (or those issued by chains that end in a self-signed certificate) would fail this check.
I have a question regarding validation of digital signatures using a self-signed certificate:
The following tutorial works for me:
http://www.oracle.com/technetwork/articles/javase/dig-signature-api-140772.html
However, when a X.509 certificate is self-signed, how can a receiver trust certificate data attached to an XML message? Any one can generate a self-signed cert and claim to be the same sender. The validation in the above tutorial always returns true. Sender’s cert must be loaded to receiver’s truststore, so receiver can use whatever in the truststore to validate signed doc. I cannot find any reference for such a scenario.
Your understanding is correct - with self-signed certificates anyone can create a certificate and signature validation will be ok. The reason is that signature validation performs first of all cryptographic operation, which is completed successfully. The second step is to validate the certificate itself AND also it's origins. When the CA-signed certificate is used, the certificate is validated using CA certificate(s) up to trusted CA (or known root CA). With self-signed certificate validation is not possible. In the above tutorial the procedure of certificate validation was skipped for simplicity as it's quite complex and beyond the scope of tutorial.
The problem you're describing is usually addressed by Public Key Infrastructures (PKI).
This is the traditional model for verifying certificates for HTTPS sites, for example. It starts with a set of trusted Certification Authorities (CAs) from which you import the CA certificates as "trusted". The entity certificates that you get are then verified against this set of trusted anchors by building a certification path between the certificate to verify and a CA certificate you know (linking the certificate to a trusted issuer, perhaps via intermediate CA certificates).
The various rules to do this are described in RFC 5280. The PKI system doesn't apply only to web servers, but to any entity (there are additional rules for web servers to verify that they're the one you want to talk to, on top of having a valid certificate).
(In particular because the choice of which CA certificates to trust is often done on behalf of the user, at least by default, by the OS or browser vendor, this model isn't perfect, but it's the most common in use.)
Alternatively, there's nothing wrong with establishing a list of self-signed certificates you would trust in advance.
Either way, you need to pre-set what you trust by mechanisms out of bands (e.g. by meeting someone you trust and using the certificate they give you in person).
This PKI model goes hand-in-hand with the X.509 format thanks to the notion of Issuer DN and Subject DN. You could have other models, for example relying on PGP certificates, where you would build a web of trust; you would still need an initial set of trusted anchors.
For XML-DSig in Java, you should implement a X509KeySelector that only returns a key that you trust. In a simple scenario, where you have a pre-defined set of self-signed certificates you trust, you can iterate over a keystore containing those trusted certificates. Otherwise, use the Java PKI Programmer Guide (as linked from the tutorial you've used).