Gamified Intelligent Cyber Aptitude and Skills Training (GICAST)
Gamified Intelligent Cyber Aptitude and Skills Training (GICAST)

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Gamified Intelligent Cyber Aptitude and Skills Training (GICAST)

1.1 Plaintext and ciphertext

This section is part of the amber and green pathways.

Figure 2

As in previous weeks, there is some terminology we need to introduce:

  • plaintext – information that can be directly read by humans or a machine (this article is an example of plaintext). Plaintext is a historic term pre-dating computers, when encryption was only used for hardcopy text, nowadays it is associated with many formats including music, movies and computer programs
  • ciphertext – the encrypted data
  • a cipher – the mathematics (or algorithm) responsible for turning plaintext into ciphertext and reverting ciphertext to plaintext (you might also see the word ‘code’ used – there is a technical difference between the two but it need not concern us now)
  • encryption – the process of converting plaintext to ciphertext (occasionally you may see it called ‘encipherment’)
  • decryption – the process of reverting ciphertext to plaintext (occasionally ‘decipherment’).

Table 1 The functional components of encryption (see Figure 3 for a visual representation)

Key = openlearn2020

Cipher = Blowfish

Plain text:

ciphertext – the encrypted data. Encrypted data is represented as a string of readable characters except that they are unintelligible

Encrypted text:


This diagram shows the information from Table 1 in visual form. It shows an upside down T-shaped funnel, where the ciphertext is inputted at one end of the T. The key and cipher are combined and fed into the funnel from above, meeting the ciphertext in the middle of the T. The encrypted text is then seen coming out of the other end.
Figure 3 The functional components of encryption

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371