Encryption is the process of encoding data to prevent unauthorized access.

Decryption is the process of decoding the data.

Substitution ciphers are examples of symmetric encryption because they use the same key for both encryption and decryption.

Public key encryption uses a pair of keys: a public key for encryption and a private key for decryption. The sender uses the public key to encrypt the message, and receiver uses their private key to decrypt it. Public key encryption is the primary method of encryption today because of its high level of security.

Symmetric cryptography uses the same secret key to encode and to decode a message, and it's been around for thousands of years. Its weakness is that the key becomes another message that needs to be transmitted securely.

SSL/TLS (secure sockets layer/transport layer security) is the standard used for cryptographically secured information transfer on the Internet.

Certificate authorities are organizations that issue digital certificates to verify who owns the encryption keys used for secured communications. Instead of trusting that the website is who they say they are, you now have to trust that the Certificate Authority is reliable.

Malware is software that was designed to harm or take partial control over your computer.

Keylogging software is a kind of malware that records every key pressed by a user.

A computer virus is a type of malware that spreads and infects other computers. Viruses can attach themselves to legitimate programs.

Antivirus or anti-malware software is software designed to scan your files and Internet transmissions looking for malware.

A firewall is a security system that controls the kinds of connections that can be made between a computer or network and the outside world.

Phishing is a common security attack in which the victim is tricked into giving up personal information or downloading malware.

A DDoS (Distributed Denial of Service) attack uses a virus to flood a server with many requests from many computers at once so that users of that server are denied service.

A rogue access point is a wireless access point that gives access to a secure network without the authorization of the network administrator.