C tutorial

Simple 'hello' program. September 2019

1) Create file hello.c

vi hello.c

In vi text editor press key i. Text editor will enter in edit mode and you can type text.

#include <stdio.h>

int main(int argc, char *argv[])


printf("Hello, World!\n");


After editing the text press Esc. Text editor will enter in command mode. For save text to file type :w and press Enter. For quit from text editor type :q and press Enter.

Next read the "C tutorial" article.

Written by: Askar Azhibaev.

New CA root certificate

Issued new CA root certificate. August 2019

Please note that the CA root certificate has been updated.

The certificate supports RSA 4096 bit encryption to improve security. Please follow the instructions to install the new certificate.

Written by: Askar Azhibaev.

Secure access with https in Firefox

Installation of the free SSL certificate in Firefox browser. February 2019

The SSL certificate confirms the authenticity of the site and provides secure communication with the site. All data transmitted over the network is encrypted with the certificate. Therefore, you can be sure that your data will not be read during transmission over the network. You also know that you are viewing the pages of this site, and not the fake site.

For the purpose of testing the certificate is more convenient to use the Firefox browser. When you click on the certificate link 9o1d.crt, the browser will open the dialog window

Downloading certificate
Figure 1. Downloading Certificate dialog window of Firefox.

Check the box to the menu item "Trust this CA to identify websites", as shown in the picture.

When you click on the "View" button, you can view the certificate.

View certificate
Figure 2. View Certificate.

It shows: certificate name "sms_ca", serial number and checksum. They must match this picture.

If everything matches, close these dialogs with confirmation of the changes.

To check, type the address https://9o1d.com in browser.

The site should open and a green padlock will appear in the browser bar. When you click on the padlock, information about encryption of the connection will be displayed.

Green padlock
Figure 3. Green padlock of the connection.

You can also read more information about the certificate used for the connection.

Additional information
Figure 4. Additional information about the certificate

If you want to remove the certificate, you need to open the browser settings and enter the installed certificates menu. There are many paid certificates. Find the certificate "sms_ca" and click the "Delete" button. Of course, after that you will not be able to establish a secure connection to the site, but if you need to, you can reinstall the certificate.

Deleting certificate
Figure 5. Deleting certificate

Firefox browser uses its own certificate storage. Other browsers can use their own certificate storage or system shared certificate storage. How to install the certificate in the system shared certificate storage, you can read in "How to install SSL certificate in the system shared certificate storage" article.

How to test the certificate with Linux tools, You can read in the "Test SSL certificate in Linux command console" article.

Screenshots are used with permission from Microsoft.

Written by: Askar Azhibaev.

About Me

Askar Azhibaev. Software Engineer.


How to install certificate:

Download SSL certificate: 9o1d.crt

OR get the same from OneDrive: 1drv.ms/9o1d.crt

+ you can register a free account on OneDrive:

Register a free account on MS OneDrive
OneDrive is a trademark of Microsoft Corporation

OR copy SSL certificate text:
(select all text, , paste to any text editor, save as "9o1d.crt" and test)

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