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| -rw-r--r-- | notes/algorithms.tex | 20 | ||||
| -rw-r--r-- | notes/cyber.tex | 76 | ||||
| -rw-r--r-- | notes/data-rep.tex | 195 | ||||
| -rw-r--r-- | notes/legal.tex | 50 | ||||
| -rw-r--r-- | notes/paper.tex | 20 |
5 files changed, 350 insertions, 11 deletions
diff --git a/notes/algorithms.tex b/notes/algorithms.tex index 581a5e5..c745b72 100644 --- a/notes/algorithms.tex +++ b/notes/algorithms.tex @@ -84,3 +84,23 @@ fewer comparisons will be made. \subsection{Bubble sort} \subsection{Merge sort} + +\section{Programming languages} + +Programming languages are useful to humans in writing algorithms for +computers to run. There are \textit{high level languages} (such as +Python, Haskell, and C) which are easier for humans to write and +understand, \textit{low level languages} (assembly code) which are +human readable but directly represent machine code, and machine code +which is not readable by humans as it is binary code but is the only +information the computer actually understands and runs. + +Some languages (such as C) are \textit{compiled}. This involves the +entire \textit{source code} being turned into a machine code file by +the compiler. Other languages (such as Python) are +\textit{interpreted}. Here, an interpreter turns a line of code into +machine code, runs it and then moves onto the next line. The benefit +of a compiler is that once compiled, the machine code file is very +fast to run. However, an interpreter offers easier development as +there are no long compile times but it is slower than code that is +already compiled. diff --git a/notes/cyber.tex b/notes/cyber.tex new file mode 100644 index 0000000..efa62ff --- /dev/null +++ b/notes/cyber.tex @@ -0,0 +1,76 @@ +\chapter{Cyber security} + +Cyber security is the study of the relation between computers, +networks, and malicious threats and attacks that they are vulnerable +to. + +\section{Threats} + +\begin{itemize} + \item \textit{Social engineering} involves exploiting people + directly for access or information. \textit{Blagging} involves + obtaining information through deception or impersonation, such + as calling someone whilst posing as a friend. + \textit{Phishing} is posing as a legitimate organisation to + obtain personal information, generally through email. + \textit{Pharming} involves a bogus website that imitates a + legitimate one. \textit{Shouldering} involves watching + somebody enter their personal information. + \item \textit{Malicious code} is code written to do bad. A + \textit{virus} does damage on a computer and spreads itself on + a user's device over the internet. \textit{Spyware} is + software that monitors, logs, and sends information to the + spy. For example, a keylogger may record every key a user + presses and send it to the spy so that information such as a + password can be extracted. \textit{Adware} is a program that + is designed to show the user advertisement and a + \textit{Trojan} is any malware that poses as a legitimate + software. + \item \textit{Weak passwords} or \textit{misconfigured access + rights} may allow an attacker easy access to unauthorised + data. Access rights would normally restrict certain + information from certain users. + \item \textit{Removable media} such as a DVD or USB flash drive is + a vector by which malware can easily spread, particularly when + distributed, such as at a public event. + \item Unpatched or outdated software may contain vulnerabilities, + as well as normal software with recently discovered + vulnerabilities which an attacker could exploit. +\end{itemize} + +\section{Threat prevention} + +\subsection{MAC Address filtering} + +A \textit{MAC Address} is unique to each device. Filtering MAC +Addresses could mean only allowing authorised devices to connect to +the network (\textit{whitelisting}) or blocking certain devices from a +network (\textit{blacklisting}). However, this is bypassable through +MAC address \textit{spoofing}, where a device can appear to have a MAC +address other than its own. + +\subsection{Firewall} + +A firewall blocks internet activity. This may be blocking access to +certain sites, or preventing external activity from potential +attackers. + +\subsection{Authentication} + +Authentication is the validation of identity through credentials. The +most common form of this is through a username and password. It can +also be through physical objects such as cards (such as credit card) +and through biometric methods such as fingerprints. + +CAPTCHA (tests that determine if a user is a human, such as by typing +in a word in strange font) and e-mail verification (where the user +must respond to an e-mail only they could have received) can also be +used as authentication and to ensure that the user is human and not an +automated attack. + +\subsection{Encryption} + +Encrypted data is encoded in such a way that only the sender and +recipient and sometimes only recipient can decode the data and read +the information. To anyone else (such as an eavesdropper), the data is +meaningless. diff --git a/notes/data-rep.tex b/notes/data-rep.tex new file mode 100644 index 0000000..f2f5ef4 --- /dev/null +++ b/notes/data-rep.tex @@ -0,0 +1,195 @@ +\chapter{Data representation} + +\section{Metadata} + +Metadata means data about data. It is the information stored in a file +that is not part of the main information, but instead important +properties and data of the file, such as the author name of a PDF +document. Although we do not take it into account when calculating +file size, it is important to realise that in the real world, it would +be there. + +\section{Character encoding} + +The \textit{American Standard Code for Information Interchange} +(ASCII) is a character encoding standard. It is comprised of +a \textit{character set} which contains characters and numerical +representations of each of them, so that they can be processed and +stored by a computer. Standard ASCII uses 7 bits to represent each +character and can thusly store 128 characters (127 characters and 1 +null character). The letter A in ASCII is character 64 ($0100000_2$), +allowing for easier human representation of the rest of the alphabet, +which increments from 64. + +Extended ASCII uses 8 bits to store each character and thus contains +256 characters (255 characters and 1 null character), allowing for +more than the limited alphabet standard ASCII contains by including +more symbols and some accented characters. This however, is quite +limited in comparison to Unicode which is a significantly larger set +which allows for character encoding in many languages and many symbols +such as emoji characters. Unicode is also compatible with many more +devices. The drawback to extended ASCII and even moreso to Unicode is +that they require more space to encode characters. + +\section{Images} + +A \textit{bitmap} (such as jpg, png) image is made up of rows of +pixels, each with a colour value. The resolution of the image, the +$\mbox{width}\times\mbox{height}$ of pixels, determines the detail the +image may contain. The colour depth is the number of bits of +information that each colour is encoded with. As with 7 bit ASCII, +the number of colours that a pixel can possibly have is determined by: + +\begin{equation} + \mbox{\textit{Number of colours}} = 2^{\mbox{\footnotesize Bit\ depth}} +\end{equation} + +For example a 4 bit depth would mean that each pixel could store one +of 16 colours. As this is all of the information an image file stores, +we can deduce that: + +\begin{equation} + \mbox{\textit{File size}} = + \mbox{width}\times\mbox{height}\times\mbox{bit depth} +\end{equation} + +A \textit{vector} image does not use pixels, but instead mathematical +descriptions of shapes to form an image. This means that whilst +zooming into a bitmap image we lose quality as resolution decreases, +this is not the case for vector images. However, vector images could +not represent a photograph and are generally used for design, +animation, or games. + +\section{Sound} + +A \textit{microphone} transforms vibrations in the air (sound) into an +analogue signal (\textit{voltage}). Digital circuitry can take a +\textit{sample} of this analogue signal at set intervals, thus +producing a close representation of the original. The +\textit{resolution} of a sound file is based on the number of possible +values a single sample can have, much like colour depth, where the +resolution is measured in bits. The \textit{sample rate} (measured in +Hertz (Hz), meaning `per second') is the number of samples taken per +second. By multiplying the sample rate by the time of the recording in +seconds, we have the number of samples taken. Then by multiplying this +by the number of bits each sample requires (the resolution) we have +the file size. + +\begin{equation} + \mbox{\textit{File size}} = + \mbox{sample rate}\times\mbox{resolution}\times\mbox{time in + seconds} +\end{equation} + +\section{Data compression} + +If files such as image, sound, or perhaps video were stored +uncompressed then they would take a lot of space on hard drives and +require longer to transfer over a network. Therefore, data compression +is generally used which involves using algorithms to reduce the size +of a file. \textit{Lossless compression} simply reduces the size of a +file and we will examine two example of this. \textit{Lossy +compression} +\footnote{\url{https://en.wikipedia.org/wiki/Data_compression}} +involves removing data such as removing quiet tones from an audio +file. + +\subsection{Run length encoding} + +Run length encoding is a form of compression where repeated values are +compressed. For example, take the binary +\begin{align*} + 111110000001110000 +\end{align*} +by compressing the runs where a zero or a one is repeated, it can +become +\begin{align*} + (5,1),(6,0),(3,1)(4,0) +\end{align*} + +\section{Huffman encoding} + +Huffman describes a method of encoding text. Suppose we have the text +\begin{align*} + repetitive +\end{align*} +We want to create a Huffman tree by writing out each character and the +number of times it occurs at the bottom. Then we join together the two +lowest numbers and add their number of occurrences. We keep doing this +until there is one number left. This ensures that each the letters +that occur the most are closest to the top of the tree. Each branch is +then labelled zero or one, depending on whether it goes left or right +respectively. Each letter then has a new code, based on the path from +the top of the tree to it. + +%% requires package \usepackage[edges]{forest} +%\begin{forest} +% for tree={ +% grow=south, +% s sep=7mm +% } +% [rpveit (10) +% [rpve (6) +% [e (3)] +% [rpv (3) +% [ rp(2) +% [r (1)] +% [p (1)] +% ] +% [v (1)] +% ] +% ] +% [it (4) +% [i (2)] +% [t (2)] +% ] +% ] +% ] +%\end{forest} + +\begin{tikzpicture} + \node at (0,0) (top) {rpveit (10)}; + + \node at (-2, -1.5) (2a) {rpve (6)}; + \node at (4, -3) (2b) {it (4)}; + + \node at (-1, -3) (3a) {rpv (3)}; + \node at (-2, -4.5) (3b) {rp (2)}; + + \node at (-6, -6) (e) {e (1)}; + \node at (-4, -6) (r) {r (1)}; + \node at (-1, -6) (p) {p (1)}; + \node at (1, -6) (v) {v (1)}; + \node at (3, -6) (i) {i (2)}; + \node at (5, -6) (t) {t (2)}; + + + + \draw (top) to node[above]{$0$} (2a); + \draw (3a) to node[above left]{$0$} (3b); + + \draw (top) to node[above]{$1$} (2b); + \draw (2a) to node[above right]{$1$} (3a); + + \draw (3b) to node[above]{$0$} (r); + \draw (2b) to node[above left]{$0$} (i); + \draw (3b) to node[above]{$0$} (r); + \draw (2a) to node[left]{$0$} (e); + + \draw (3b) to node[above right]{$1$} (p); + \draw (2b) to node[above right]{$1$} (t); + \draw (3a) to node[above]{$1$} (v); +\end{tikzpicture} +Here, the letter e has the code $00$, the letter r has the code +$0100$, the letter p has the code $0101$, and so on, as these are the +paths from the top of the tree to the letter in question. If we were +encoding with standard ASCII (7 bits per character) then the size of +the sting would be $7\times 10 = 70\ bits$ (as there are 10 +characters). + +Using the Huffman tree we have generated we can encode $repetitive$ as +\begin{align*} + 0100000101001110111001100 +\end{align*} +This uses $25\ bits$, which is a $(70-25)\div(70)\times 100 \approx +64.3\%$ saving. diff --git a/notes/legal.tex b/notes/legal.tex new file mode 100644 index 0000000..5b74b79 --- /dev/null +++ b/notes/legal.tex @@ -0,0 +1,50 @@ +\chapter{Impacts of computing} + +Computing and computer science has very clearly transformed our world +in many ways. + +\section{Legal} + +Computing has many legal consequences. The ways in which the law +applies in the general world is very different from the internet, +such as a new ability to distribute information. There are many laws +which apply to the internet, but here are a few: + +\subsection{Data Protection Act (1998)} + +The Data Protection Act makes it a requirement for organisations to +follow strict guidelines when storing people's sensitive or personal +data. A modern law similar to this is the \textit{General Data +Protection Regulation} (GDPR) (2016) is more up to date. + +\subsection{Computer Misuse Act (1990)} + +The Computer Misuse Act makes it it illegal to gain +\textbf{unauthorised} access to a computer, or to use a computer in +committing an offence. + +\subsection{Copyright, Designs and Patents Act (1988)} + +The Copyright, Design and Patents Act gives people or businesses +ownership of their creative work, such that they have complete +commercial rights to it, thereby making \textit{piracy} of content or +software illegal. + +\section{Ethics} + +Ethical considerations involve thinking about the aspects of computing +that are good or bad, or right or wrong. What is ethical or +moral has no strict definition, although the law is based on ethics. +An example of ethical considerations might be terms of service, +offensive language and freedom of speech, the increasing use of phones +with young people, or the sourcing of materials for use in electronics +from places such as the Congo \footnote{Rory Stewart OBE: "Failed +States - and How Not to Fix Them"; Yale University; +\url{https://www.youtube.com/watch?v=zMXXJqvMdk4}}. Thus ethics are +open to interpretation and your own opinion. + +\section{Environment} + +Computing has many environmental impacts. From electricity usage to +e-waste produced by the ongoing release of new devices, technology has +an immense impact on our environment. diff --git a/notes/paper.tex b/notes/paper.tex index 48dce83..b28234a 100644 --- a/notes/paper.tex +++ b/notes/paper.tex @@ -52,7 +52,7 @@ top=0.5in, bottom=0.8in ]{geometry} \titleformat{\section}{\large}{}{0em}{} \titleformat{\subsection}{\bfseries}{}{0em}{} -\titleformat{\chapter}{\vspace{-2cm}\tt\huge\itshape}{}{0em}{} +\titleformat{\chapter}{\vspace{-2cm}\tt\huge\itshape}{\thechapter:}{5mm}{} \begin{document} \begin{titlepage} @@ -75,6 +75,9 @@ top=0.5in, bottom=0.8in ]{geometry} \input{hardware.tex} \input{software.tex} \input{networks.tex} +\input{legal.tex} +\input{cyber.tex} +\input{data-rep.tex} \chapter{Acknowledgements, about, and license} Notes for AQA GCSE Computer Science.\\ @@ -97,15 +100,10 @@ time on trying to answer questions and play with the ideas discussed. \vspace{2cm} -\begin{myquote} - - This work is licensed under the Creative Commons - Attribution-ShareAlike 4.0 International License. To view a copy - of this license, visit - \url{http://creativecommons.org/licenses/by-sa/4.0/} or send a - letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, - USA. - -\end{myquote} +This work is licensed under the Creative Commons +Attribution-ShareAlike 4.0 International License. To view a copy of +this license, visit +\url{http://creativecommons.org/licenses/by-sa/4.0/} or send a letter +to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA. \end{document} |