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Encryption is the process of disguising a message so that it cannot be understood by anyone but its intended recipient. Encryption requires the use of a key. The key is the secret that defines how the message has been disguised.

• Unencrypted messages are referred to as plaintext messages.
• Encrypted messages are known as ciphertext.

A simple method of encryption is a technique known as the Caesar cipher. The cipher works by using a numerical key. Each plaintext letter is replaced by a new letter, the one found at the original letter's position in the alphabet plus or minus the value of the key.

For example, a key value of plus three would change the plaintext message ‘see you tonight’ to the ciphertext message ‘vhh brx wrqljkw’.

To decrypt the message the process is reversed.

Although this is a good example of encryption, today much more complicated algorithms are used to encrypt messages.

Encryption in use

Most communications sent via the internet are encrypted in some way:

• purchases made online are encrypted to try to prevent theft of credit card details
• tools enable a user to encrypt a document, such as a spreadsheet, before sending it to a colleague via the internet
• satellite TV transmissions are encrypted to prevent users who do not subscribe from watching TV shows

XOR encryption

Another method for encrypting text is to use the XOR method.

To encrypt a message:

1. select a random 8-bit binarypattern
2. convert each character of the message into binary ASCII
3. use XOR logic to create a new code
4. convert the new 8-bit binary number into an ASCII character

For instance, using a randomly selected 8-bit binary pattern of 00110110 we can encrypt the string ‘Computer’.

Convert each character into 8-bit ASCII

C = 01000011

o = 01101111

m = 01101101

p = 01110000

u = 01110101

t = 01110100

e = 01100101

r = 01110010

For each character use XOR (exclusive OR) to compare the ASCII code to the randomly selected pattern. If exactly one of the two characters you are comparing is a 1, place a 1 in that position in the new code. If both are 0, or if both are 1, then place a 0 in that position.

Here is the conversion for the letter ‘C’.

The new character generated is 01110101, which converts to the ASCII character ‘u’. Sometimes the character will be a letter, number, or symbol, or it could be a hidden character such as NULL, SPACE or LINE BREAK.

All of the characters are converted this way using the same 8-bit pattern that was used to convert the first character.

The encrypted message would display ‘uY[FCBSD’.

To decrypt a message, repeat the method using the same 8-bit binary pattern.