Questions tagged [certificates]

A piece of data used in public key cryptography (specifically public key infrastructures) 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. For questions specifically about [x509], [certificate-authority], or [public-key-infrastructure], please use those tags.

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1271 votes
3 answers

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. ...
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367 votes
6 answers

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 ...
273 votes
18 answers

Provide subjectAltName to openssl directly on the command line

Is it possible to provide a subjectAltName-Extension to the openssl req module directly on the command line? I know it's possible via a openssl.cnf file, but that's not really elegant for batch-...
259 votes
7 answers

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 ...
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208 votes
7 answers

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 ...
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167 votes
4 answers

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?
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159 votes
4 answers

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' (...
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147 votes
5 answers

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?
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143 votes
14 answers

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 ...
129 votes
7 answers

Let's Encrypt for intranet websites?

Many companies have intranet websites that are not reachable via the internet. Usually they just use a self-signed certificate, which causes a bad habit for the users since they get used to just ...
115 votes
6 answers

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 ...
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115 votes
4 answers

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....
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109 votes
10 answers

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 ...
108 votes
8 answers

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 ...
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100 votes
4 answers

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 ...
96 votes
5 answers

Are there any downsides to using Let's Encrypt for a website's SSL certificates?

On the advantages side, I see several benefits to using the Let's Encrypt service (e.g., the service is free, easy to setup, and easy to maintain). I'm wondering what, if any, are the disadvantages to ...
94 votes
10 answers

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 ...
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94 votes
4 answers

Should I revoke no longer used Let's Encrypt certificates before destroying them?

The Let's Encrypt documentation recommends that when a certificate’s corresponding private key is no longer safe, you should revoke the certificate. But should you do the same if there are no ...
90 votes
12 answers

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 ...
89 votes
4 answers

SSL Certificate framework 101: How does the browser actually verify the validity of a given server certificate?

(Sorry I know this is a complete noob question and at the risk of posting a somewhat duplicate topic. I have a basic understanding of public/private key, hashing, digital signature... I have been ...
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88 votes
2 answers

Why would I choose SHA-256 over SHA-512 for a SSL/TLS certificate?

I'm looking to renew an SSL (okay, TLS) wildcard certificate with a well-known service. I need to provide a CSR, which I have created using a 2048-bit key. I also need to choose a signature hash. The ...
88 votes
4 answers

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

Can I simply build a webserver, make its hostname "", 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 ...
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88 votes
2 answers

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 ...
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87 votes
5 answers

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 ...
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86 votes
2 answers

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?
82 votes
1 answer

Is Starbucks spoofing me?

When I connected to Starbucks's Wi-Fi, I got a security alert from MS Outlook that looks like this: I looked up, but there's no mention of this thing anywhere. This does not ...
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77 votes
6 answers

Should I reject a CSR when the host emailed me the private key for SSL certificate request?

I just requested a CSR from my shared web hosting provider, to generate a certificate which I will send back to them to install. (The certificate itself is to be generated properly by an organisation ...
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75 votes
1 answer

How can Kazakhstan perform MITM attacks on all HTTPS traffic?

There is now MITM on HTTPS traffic in Kazakhstan. But for MITM to work, other than installing the certificate, there has to be someone proxying the request, right? Will that role be played by the ...
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71 votes
2 answers

What's the difference between X.509 and PKCS#7 Certificate?

Am I correct calling file with .p7b file extension saved as 'Cryptographic Message Syntax Standard - PKCS#7 Certificates (.P7B)' in Windows - a 'PKCS#7 certificate'? Or is it better called 'X.509 ...
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70 votes
4 answers

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?
69 votes
4 answers

Understanding 2048 bit SSL and 256 bit encryption

On DigiCert's page, they advertise a 2048 bit SSL with a 256 bit encryption: What exactly is the difference here and why are two encryption bits ...
  • 857
69 votes
4 answers

How does the digital signature verification process work?

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 ...
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66 votes
7 answers

Why would a school need to install certificates on student laptops?

This question indicates parents are to buy laptops for a school to install software and certificates. I am seeking to understand reasons for site certificates installation: Why would site ...
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66 votes
3 answers

Why is Firefox (and only Firefox) reporting that my connection is insecure on multiple sites?

After installing Firefox 54.0.1 on my work laptop, the first page I see warns me that "Your connection is not secure" when opening "The owner of Firefox has configured their ...
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62 votes
4 answers

Is there a way to make sure my government does not swap out SSL certificates?

I was recently wondering whether there exists a way to make sure my government is not swapping out SSL certificates in order to intercept the traffic. I know almost all browsers are complaining in ...
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62 votes
4 answers

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 ...
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61 votes
1 answer

How does my browser inherently trust a CA?

I am reading this post and not understanding the answer. The answer ends with the words ...your browser can verify one cert against the next, all the way to the root CA, which your browser ...
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60 votes
3 answers

Why is this certificate for Imgur only valid for one day?

I'm connected over a café WiFi and received a warning from my mobile browser. When I looked further, it seems like the certificate is only valid for one day, which seems super suspicious.   It ...
60 votes
2 answers

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 ...
  • 949
59 votes
2 answers

Can I restrict a Certification Authority to signing certain domains only?

Is it possible to create a CA certificate (even unsigned), which is only allowed to sign certificates for specific limited domain(s), so that it can't be misused for other domains?
  • 1,741
58 votes
1 answer

Does a client certificate identify the owner to unrelated websites?

If I install a client certificate in my browser, which websites can see any information about this client certificate or the CA that issued it? I once visited an ssl diagnostic site that immediately ...
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57 votes
7 answers

Can a CA decrypt HTTPS traffic?

My state has made a statement that in case my country will be disconnected from the world's CAs, it is necessary to install its own state certificates. In many forums, information has flashed that in ...
  • 1,005
56 votes
2 answers

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?
54 votes
3 answers

4096 bit RSA encryption keys vs 2048

Where do 4096 bit RSA keys for SSL certs currently stand in terms of things like CA support, browser support, etc? In the overall scheme of things is the increased security worth the risk of 4096 bit ...
  • 2,707
52 votes
2 answers

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 ...
  • 2,813
52 votes
2 answers

What is the difference between SSL and X.509 Certificates?

I used openssl to create a X.509 certificate but I don't quite understand the relationship between a X.509 and a SSL certificate. Are they the same? Is a SSL certificate just a X.509 certificate that ...
user avatar
51 votes
2 answers

Why aren't infinite-depth wildcard certificates allowed?

As far as I can tell, an SSL certificate for * is good for and, but not Wildcards certificates cannot have *.* as their ...
  • 8,257
49 votes
4 answers

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 ...
user avatar
49 votes
3 answers

Generate CSR from existing certificate

Can we generate the CSR (certificate signing request) used for certificate signing from the signed certificate? It should work with the original private key when signed again with different authority.
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47 votes
5 answers

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 ...
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