A Security Certificate (also known as a public-key certificate) is an electronic document used to prove ownership of a public encryption key.
A Security Certificate is used in TLS to associate encryption keys with internet domains (such as howtouselinux.com).
A security certificate is a small data file used as an Internet security technique through which the identity, authenticity and reliability of a website or Web application is established.
Why do we need a security certificate?
Encryption: SSL/TLS encryption is possible because of the public-private key pairing that SSL certificates facilitate. Clients (such as web browsers) get the public key necessary to open a TLS connection from a server's SSL certificate.
Authentication: Security certificates verify that a client is talking to the correct server that actually owns the domain. This helps prevent domain spoofing and other kinds of attacks.
How do security certificates work?
Security certificates are issued by certificate authorities. They are trusted third parties between a browser and a website and vouching that a given encryption key should be used to encrypt data being sent to the website’s domain.
Browser software will trust a few hundred certificate authorities—for example, Comodo, DigiCert etc.
When a trusted certificate authority vouches for a key and domain, it assures our browser that it’s communicating with the right website using the right encryption key, thereby blocking an attacker from presenting a malicious website or certificate.
How to get a security Certificate
generate a key pair
use this key pair to generate a certificate signing request (CSR) that contains the public key and domain name of our website
upload the request to a certificate authority
download the certificate and install it on our web server along with the key pair
Expiration of security Certificates
Security certificates have a finite lifespan (typically in years or months) after which they must be reissued by the certificate authority.
Browsers will warn a user when visiting a website with an expired or revoked certificate.
Are Security Certificates safe?
Security certificates rely on various things to be secure and trustworthy — the strength of the algorithm to create the signature and the competence of the issuing authority, for example.
These naturally improve over time as knowledge and research findings spread, just as weaknesses in older methods appear. There have been cases of certificate spoofing and there may be again, but the likelihood is ever-decreasing.