A level revision

Security and the internet

Firewall

A firewall is used to prevent unauthorised access to or from a network. Firewalls can be implemented using both hardware and/or software. The firewall creates a barrier between data which enters and leaves the network. Known as packet inspection, the firewall inspects each passing packet looking at the data it contains and the header information. If the packet fails to conform to pre-set rules or packet filters set by the network administrators it will be rejected.

A firewall can also act as a proxy server which intercepts data entering and leaving the network hiding the true network addresses form outside the network.

Encryption

Encryption is the process of using an algorithm to code a message into 'ciphertext'. Decryption is the decoding of the cipher text backing to plain text. A key is used to scramble and unscramble the message.

In symmetric encryption the same key is used to encrypt and decrypt the message whereas asymmetric encryption uses two different keys for encryption and decryption, this is also known as public key encryption.

Public key encryption

Public key encryption involves having both a public and private key. A message encrypted with one can only be decrypted by the other. Since it is near impossible to get the private key from the public key this is a very secure encryption system. When sending information in this way it is encrypted using the public key of the recipient who can then decrypt it using their private key.

Digital signatures and certificates

Digital signatures are an encrypted hash code - a mathematical summary of the document. They are sent along with the data to the recipient who then decrypts both the hash code and the document was send. The recipient computer then generates a hash code of the received document and compares it to the one sent with it, if they match the recipient and be confident the document is genuine and hasn't been changed since it was sent.

A digital certificate can be used to verify that a website is who they say they are. They are issued by a certification authority, such as VeriSign, and contain details about the company or user along with their public key which should be used for encrypting messages and digital signatures. The digital certificate is also digitally signed by the certification authority so it can be checked by the user to be the real thing.

Virus detection

Virus detection software checks files for known viruses, worms and other threats to the security of the computer.

Phishing

Phishing is an attempt to gain login and other personal details of users by forging input forms and websites. Users are sent emails that appear to be from the real company asking them to update or change their details. The emails however point the user to a fake URL which contains a copy of the website's login portal tricking users into thinking they are on the real site. Unwitting users enter their details which are then sent to the scammers.

Spam

Spam is unwanted junk email which is sent to hundreds, even thousands of email addresses at once. It is typically sent to advertise a product or service. Spam can be cut down by using a email filter to reject messages from known spam addresses, IP addresses and servers.