The Internet was originally designed for plain text communication between web browsers and servers. Hackers learn how to sniff communications and look for passwords, personal and financial information.
The solution is to use public/private key encryption to thwart the hackers. This encryption can be done by simply referencing certificate files from web browsers. The first version of this style of encryption was called SSL (Secured Socket Layers). SSL was replaced by TLS (Transport Layer Security).
Web hosts and domain registrars often provide certificates.The problem here is that hackers who gain access to the internet can place computers that intercept your web traffic and issue fake certificates.
A certificate authority is a company the verifies a certificate for a given web site.
Unfortunately, certificate authorities tend to over charge for their services. Secure certificates often cost more than web hosting services and, unfortunately, only the wealthiest of companies can afford certificates.
GNU Privacy Guard (gnupg.org) GnuPG is a complete and free implementation of the OpenPGP standard allowing users to to encrypt and sign your data and communications.
CAcert.org (www.cacert.org) CAcert.org is a community-driven Certificate Authority that issues certificates to the public at large for free.
Comodo (www.comodo.com) Comodo offers SSL Certificates and internet security services.
CA/Browser Forum (cabforum.org) CA/Browser Forum is a voluntary group of certificate authorities for SSL/TSL certificates.
Digicert (www.digicert.com) DigiCert, of Lehi, Utah offers SSL certicates and related services.
GoDaddy - SSL (www.godaddy.com) GoDaddy offers a full range of domain services and SSL certificates.