A piece of data used in public key cryptography that contains identifying information (i.e. email address or web address), a hash of a public key, and a digital signature that authenticates the data in the certificate.

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702
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3answers
360k views

How does SSL/TLS work?

How does SSL work? I just realised we don't actually have a definitive answer here, and it's something worth covering. I'd like to see details in terms of: A high level description of the protocol....
182
votes
7answers
24k views

How do certification authorities store their private root keys?

Knowledge of a CA private key would allow MitM attackers to transparently supplant any certificates signed by that private key. It would also allow cyber criminals to start forging their own trusted ...
145
votes
4answers
90k views

What exactly does it mean when Chrome reports 'no certificate transparency information was supplied by the server?'

When visiting Gmail in Chrome, if I click on the lock icon in the address bar and go to the connection tab, I receive a message 'no certificate transparency information was supplied by the server' (...
140
votes
5answers
101k views

What is certificate pinning?

I'm superficially familiar with SSL and what certs do. Recently I saw some discussion on cert pinning but there wasn't a definition. A DDG search didn't turn up anything useful. What is certificate ...
107
votes
6answers
18k views

I can't access websites that use HTTPS, instead getting the message “your connection is not private”!

I found myself suddenly unable to access websites that use HTTPS, so I contacted my service provider, and they asked me to install a certificate in the Trusted Root Certificate Authorities store. But ...
107
votes
14answers
29k views

Is there any technical security reason not to buy the cheapest SSL certificate you can find?

While shopping for a basic SSL cert for my blog, I found that many of the more well-known Certificate Authorities have an entry-level certificate (with less stringent validation of the purchaser's ...
85
votes
6answers
67k views

Does https prevent man in the middle attacks by proxy server?

There is a desktop client A connecting to website W in a https connection A --> W Somehow between A and W, there is a proxy G. A --> G --> W In this case, will G be able to get the ...
82
votes
4answers
11k views

What prevents me from buying a SSL certificate for a domain I don't control?

Can I simply build a webserver, make its hostname "google.com", create a CSR off that server, and send that to a Certificate Authority for signing? Let's say I pick the cheapest and dodgiest outfit I ...
78
votes
4answers
70k views

What certificates are needed for multi-level subdomains?

I'm working on a web site with a several levels of subdomains. I need to secure all of them with SSL, and I'm trying to determine the correct certificate strategy. Here's what I need to secure: foo....
75
votes
10answers
21k views

Why do we not trust an SSL certificate that expired recently?

Every SSL certificate has an expiration date. Now suppose some site's certificate expired an hour ago or a day ago. All the software by default will either just refuse to connect to the site or issue ...
72
votes
4answers
28k views

Are all SSL Certificates equal?

After running a few tests from Qualsys' SSL Labs tool, I saw that there were quite significant rating differences between a GoDaddy and VeriSign certificate that I have tested against. Are all SSL ...
71
votes
4answers
61k views

What is the difference between an x.509 “client certificate” and a normal SSL certificate?

I am setting up a web service through which my company will talk to a number of business customers' services. We will be exchanging information using SOAP. I would like to handle authentication with ...
69
votes
2answers
36k views

ssltest: Chain issues - Contains anchor

I've run ssltest on web application and it found "Chain issues - Contains anchor" (section "Additional Certificates (if supplied)") What does it mean? Should it be fixed? Can it be exploited?
69
votes
7answers
76k views

Certificate based authentication vs Username and Password authentication

What are the advantages and drawbacks of the certificate based authentication over username and password authentication? I know some, but I would appreciate a structured and detailed answer. UPDATE ...
66
votes
12answers
9k views

How feasible is it for a CA to be hacked? Which default trusted root certificates should I remove?

This question has been revised & clarified significantly since the original version. If we look at each trusted certificate in my Trusted Root store, how much should I trust them? What factors ...
57
votes
2answers
131k views

Difference between .pfx and .cert certificates

What is the difference between .pfx and .cert certificate files? Do we distribute .pfx or .cert for client authentication?
57
votes
4answers
7k views

Why was the private key of the Superfish certificate so easily extractable?

Robert Graham detailed on the Errata Security blog how he was able to get the private key of the Superfish certificate. I understand that attackers can now use this key to generate certificates of ...
56
votes
5answers
175k views

How can I export my private key from a Java Keytool keystore?

I would like to export my private key from a Java Keytool keystore, so I can use it with openssl. How can I do that?
54
votes
9answers
18k views

Should I change the private key when renewing a certificate?

My security department insists that I (the system administrator) make a new private key when I want a SSL certificate renewed for our web servers. They claim it's best practice, but my googling ...
53
votes
2answers
3k views

Why does Windows Ship with Expired SSL Certificates?

I am cleaning up the certificate stores on my Windows machines, and considering which certificates I should keep, and which ones I should delete. Why does a fresh install of Windows Server 2012 R2 ...
43
votes
3answers
9k views

My friend revealed both private and public keys for his server. How serious is this?

A friend of mine managed to expose both id_rsa and id_rsa.pub file from his server via apache. I mentioned to him that this is serious security issue but he brushed this off like it was no big deal. ...
42
votes
7answers
5k views

Is there any legitimate reason to install yourself as a root CA?

Follow up from comments on another question. Is there any reason as to why you might install yourself as a root CA on your own network? The only reason I can think of is forcing computers in the ...
41
votes
3answers
102k views

Understanding 2048 bit SSL and 256 bit encryption

On DigiCert's page, they advertise a 2048 bit SSL with a 256 bit encryption: http://www.digicert.com/256-bit-ssl-certificates.htm What exactly is the difference here and why are two encryption bits ...
40
votes
2answers
32k views

What is the difference between serial number and thumbprint?

I have problems to understand what is the difference between the serial number of a certificate and its SHA1 hash. The MSDN says: Serial number A number that uniquely identifies the ...
38
votes
4answers
7k views

What alternatives are there to the existing Certificate Authority system for SSL?

Whilst the current CA system works very well for a lot of people, it does put a lot of power into individual CAs' hands, and makes a CA hack potentially devastating for customers and business. What ...
36
votes
3answers
25k views

What are the risks of self signing a certificate for SSL

Let's say I sign a SSL certificate for myself, and I'm not using a certified CA. What are the risks and/or threats of doing it?
35
votes
10answers
11k views

Is anybody using client browser certificates?

Client browser certificates seem to be a nice way to protect sites from intruders - it is impossible to guess and should be harder to steal. Of course, they do not solve all the problems, but they add ...
34
votes
5answers
5k views

Should I trust a website which uses a SHA-1 HTTPS certificate?

I am on a website where I need to pay for something. This website has the following warning in the top left: This site uses a weak security configuration (SHA-1 signatures) so your connection ...
32
votes
3answers
3k views

What is an SSL certificate intended to prove, and how does it do it?

If I get an SSL certificate from a well-known provider, what does that prove about my site and how? Here's what I know: Assume Alice and Bob both have public and private keys If Alice encrypts ...
31
votes
4answers
13k views

Are there technical disadvantages in using free ssl certificates?

Note this question is related, except this one is about free SSL certs. There are providers who are offering totally free entry-level SSL certs (like StartSSL). I was wondering if they are ...
31
votes
2answers
2k views

Can a SSL certificate have longer validity period than its parent in X.509 chain?

When a X.509 certificate chain is composed of X1, X2 ... Xn and Xn is root CA, Can a certificate in lower level have longer validity period than its parents? I think that lower level should be proper ...
31
votes
3answers
27k views

Why is 'avast! Web/Mail Shield Root' listed as CA for google.com?

I just noticed something weird in my browser: the certificate for www.google.com has been issued by avast! Web/Mail Shield Root. Should I be worried? I am using avast! Antivirus so it's probably a ...
30
votes
3answers
9k views

Which CA issued certificate for https://www.google.com

I installed Kaspersky internet Security 2016 on my laptop; in Firefox and Edge the root issuer is Kaspersky Anti-Virus Personal Root Certificate. but in chrome the root issuer is GeoTrust. in my ...
30
votes
4answers
5k views

Corporate computers have own corporation's cert as trusted CA; should I consider all traffic compromised?

By my admittedly limited understanding of how HTTPS/TLS works, the end user (me) initiates a connection with a remote server which signs every one of its messages with a public key. This public key ...
30
votes
5answers
20k views

Where to get an SSL certificate for personal website?

I would like to use https to login to my personal webpage (which is on shared hosting). So I went over to google and started searching for sollutions. Eventualy I found out that I need an SSL ...
30
votes
2answers
4k views

Digital Certificate deployment: using two certs for each user?

At a large enterprise environment I have come across a deployment approach for Digital Certificates where each user is issued two (2) key pairs: One for signing documents, emails, etc. that is ...
29
votes
2answers
5k views

Is it safe to send SSL certificates via email?

I just ordered a cheap Comodo PositiveSSL Certificate via a UK reseller, and I was rather surprised to find that the following files were emailed to me automatically, in a zip file: Root CA ...
29
votes
4answers
201k views

How do I clear cached credentials from my Windows Profile?

Windows seems to be saving my credentials for a variety of applications (terminal servers, etc) and I'd like to purge this data. How can I backup and purge this data?
28
votes
3answers
2k views

Does any technology prevent a CA unilaterally revoking a certificate?

As far as I can tell, a CA is in a position to unilaterally revoke a certificate via the standard mechanisms (CRL, OCSP). In an increasingly TLS world, what current technology stops a CA shutting ...
28
votes
4answers
2k views

Can any CA sign any domain?

Can any CA sign any cert for any domain? If the answer is yes, what prevents having two different CAs creating a valid cert for the same domain? Does that mean that the whole TLS security has the ...
28
votes
4answers
41k views

Expired SSL Certificate Implications

What are the security implications of an expired SSL certificate? For example if an SSL certificate from a trusted CA has expired will the communication channel continue to remain secure?
27
votes
4answers
18k views

What vulnerabilities could be caused by a wildcard SSL cert?

In a comment on this answer, AviD says: "There are numerous security issues with wildcard SSL certs." So, what are the problems? I understand that the same private key is being used in multiple ...
27
votes
3answers
2k views

Is there a security issue in using the same certificate for all a company's services?

We are a small startup. One of our products is a B2B web service, accessible through its https://service.example.com canonical URL. For testing purposes, that service also runs on different testing/...
27
votes
1answer
52k views

Can a CSR be created in OpenSSL with SHA2?

Can a CSR be created in OpenSSL with SHA2? If so, what would the command be and what does this tell the CA, if anything? If you could create a CSR using SHA2 would it "tell" the signing CA to use it ...
27
votes
5answers
29k views

What ciphers should I use in my web server after I configure my SSL certificate?

There are many great questions that ask what is the best certificate to use for a website; but once the certificate is purchased, there is also the possibility to choose or edit the Cipher list. ...
27
votes
2answers
4k views

Why aren't infinite-depth wildcard certificates allowed?

As far as I can tell, an SSL certificate for *.example.com is good for foo.example.com and bar.example.com, but not foo.bar.example.com. Wildcards certificates cannot have *.*.example.com as their ...
26
votes
1answer
2k views

Why does Firefox not trust this US government SSL certificate?

Shouldn't this be a trusted certificate considering it's a wildcard SSL certificate? That is, shouldn't *.delaware.gov cover www.corp.delaware.gov?
26
votes
4answers
38k views

how digital signature verification process works

I am not able to understand that how the digital signature is verified. I know that digital signature will be attached to the message and sent by sender to receiver. then receiver uses the public key ...
26
votes
2answers
10k views

What are the advantages of EV Certificate?

What are the various advantages of using extended validation (EV) certificates than normal certificates which also provide comparatively high degree of encryption like RC4, 128 Bit? I know that the ...
25
votes
10answers
5k views

Can an HTTPS site be malicious or unsafe?

I know it's possible for a computer to be infected just by visiting a website. I also know that HTTPS websites are secure. To my understanding, "secure" here refers to "immune to MITM attacks", but ...