Certificates from the Ubuntu Server Guide by OnWorks

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5. Certificates‌

One of the most common forms of cryptography today is public-key cryptography. Public-key cryptography utilizes a public key and a private key. The system works by encrypting information using the public key. The information can then only be decrypted using the private key.

A common use for public-key cryptography is encrypting application traffic using a Secure Socket Layer (SSL) or Transport Layer Security (TLS) connection. One example: configuring Apache to provide HTTPS, the HTTP protocol over SSL. This allows a way to encrypt traffic using a protocol that does not itself provide encryption.

A Certificate is a method used to distribute a public key and other information about a server and the organization who is responsible for it. Certificates can be digitally signed by a Certification Authority, or CA. A CA is a trusted third party that has confirmed that the information contained in the certificate is accurate.