Tag: sherlock holmes

Posted in Psychology & Medicine

Psychopath

Posted on by Jinavie

A common character found in psychological thrillers are those who seem to have no regard for the well-being of others, disobey social rules and act violently for seemingly no reason. They show no remorse or empathy and can be very intelligent, charming and high-functioning (although not typically). We describe these people as psychopaths, or sometimes sociopaths. To over-simplify it, a psychopath essentially has no moral conscience and do not believe in the social contract.

The terms psychopath and sociopath are often used interchangeably, but in modern psychiatry, they both fall under the diagnosis of antisocial personality disorder (ASPD). ASPD patients tend to have a long history of criminal charges, often relating to violence, chronic lying and fraud, drug use and other law-breaking actions. These characteristics may show from early childhood, with the typical psychopathic child being described as one murdering animals and being violent towards other kids. These children are often diagnosed with another disorder called conduct disorder.

Psychopaths are very popular in movies and TV shows due to their unpredictable nature, wanton violence and maniacal behaviour inflicting terror into the audience’s hearts. After all, who wouldn’t be afraid of a remorseless killer who finds enjoyment from others’ suffering? Unfortunately, many movies distort the image of the psychopath and blend in various other mental health disorders such as psychosis into the character. Sometimes psychopaths are even sensationalised, being described as an antihero.

It is true that many serial killers turn out to be psychopaths, but physical violence is not necessarily a feature of all psychopaths. A subset of “successful” psychopaths differentiate themselves by being less physically violent, appear to follow the social norm and succeed in challenging fields such as business, finances, law or even medicine. However, they will also have a pervasive disregard for others and will only care about having their way. Their lack of empathy allows them to act immorally, stabbing people in the back and lying, cheating and manipulating their way to the top. It is not some sick sexual perversion or power trips that motivate psychopaths, but impulsivity, egocentricity and gratification. To psychopaths, the aim of the game is to win, no matter the cost.

This makes you wonder. How many people around you are secretly a psychopath – one who would take advantage of you without a shred of guilt? How many people around you hide behind the mask of sanity?

(NB: Just putting it out there, Sherlock Holmes is neither a psychopath nor a sociopath. If anything he probably has an autism spectrum disorder like Asperger’s syndrome.)

Posted in Simple Pleasures of Life

Simple Pleasures of Life #29

Posted on by Jinavie

Doing absolutely nothing.

I kinda mentioned this in a previous post, but that was more in the context of taking a break. Don’t get me wrong, I LOVE doing stuff. Especially right now where all I can think of is all the stuff I’m waiting to do as soon as exams are over. But there’s a real simple joy in doing absolutely nothing. Just…sitting there, you know?

Of course I don’t mean literally nothing where you switch off your brain. That’s what you do when you watch TV (which I heartily endorse). But I mean putting down the book you’re reading or pausing that video, sitting back and getting lost in your thoughts. Maybe you’ll ponder the deep philosophies of what it means to be alive, or create an imaginary world you can adventure in.

If you don’t feel like exploring the inner workings of your mind, then get lost in your surroundings. Have you ever really taken into account what you see, hear, smell, taste and touch? Bernard Werber talked about a relaxation technique called “Opening your senses” in his books, which involves you systematically saying out loud everything you experience in the moment with each sense. For example, close your eyes and say everything you hear, to the smallest detail. Then do the same with all your other senses, you’ll notice that you’ve been missing out a lot of things in this world.

Sherlock Holmes stated that there is a great difference between seeing and observing. Try this out sometime. Have a cup of coffee at a cafe by yourself and look around you. You might see a boy and a girl making idle chit chat, but you might observe the two showing various subtle body language signs of mutual attraction. See if you can figure out a person’s job or personality or health condition just from observation. People-watching can be very fun, as long as you’re not being…you know, creepy.

So go on, drop what you’re doing, go lie in a patch of grass or sit at a cafe or wherever and just do nothing.

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Posted in Science & Nature

Cryptography: Book Cipher

Posted on by Jinavie

So far, the three ciphers introduced could all easily be cracked using frequency analysis and the Kasiski examination. Is there a cipher that is easy to implement yet difficult to break for a beginner cryptanalyst? An extremely popular and surprisingly powerful cipher is the book cipher. Essentially, the book cipher replaces a keyword with an entire book. Instead of replacing a letter for a letter or symbol in a systematic and mathematical way (such as a set shift number or using a tabula recta), the book cipher replaces letters for numbers that refer to a certain text within a book. As the only way to decode the message is to have the book, it is an extremely secure way of enciphering a message given that both parties have an identical copy of the book.

There are many variations of the book cipher. The most popular type is giving a page number, with the first letter of the page being the plaintext. A variant of this is giving a set of three numbers for every letter: the page number, the line number and the word number (or just two: page and line, then take the first letter). Ironically, this may be less secure at times as it may reveal that it is a book cipher. However, doing this for each letter makes the enciphering and deciphering process incredibly long and arduous.

A shortcut method is to refer to a word within a page (using the three-number set coordinates method described above) to shorten the ciphertext. Although this method is much easier in practice, it poses the challenge of finding a book that includes all the words in the plaintext, which may be difficult if the code is for military or espionage purposes.

Because of this, and the fact that both parties (or everyone in the ring) need identical versions of the book while not standing out too much, the most common books used are the dictionary (typically a famous version such as the Oxford Dictionary) or the bible (again, a standard version is used). These books are not only good because they incorporate a massive vocabulary, but they are also inconspicuous while being carried around in an enemy territory.

The book cipher is a very difficult code to crack for most people without advanced cryptanalysis training. Thus, the easiest way to crack is to deduce what book is the keytext. There are numerous ways to do this, but one way would be to cross-match the books of two known spies until common books are found. In the setting of spies in a foreign country, a book such as a traveller’s guide or phrasebook dictionary can be considered a likely target as it can be carried around easily while containing many words. Ergo, the secret behind cracking the book cipher is less about cryptography and more about using the science of deduction.

Posted in Science & Nature

Cryptography: Kasiski Examination

Posted on by Jinavie

The Kasiski examination can be used to attack polyalphabetic substitution ciphers such as the Vigenère cipher, revealing the keyword that was used to encrypt the message. Before this method was devised by Friedrick Kasiski in 1863, the Vigenère cipher was considered “indecipherable” as there was no simple way to figure out the encryption unless the keyword was known. But with the Kasiski examination, even the Vigenère cipher is not safe anymore.

The Kasiski examination is based on the fact that assuming the number of letters of the keyword is n, every nth column is encoded in the same shift as each other. Simply put, every nth column can be treated as a single monoalphabetic substitution cipher that can be broken with frequency analysis. Ergo, all the cryptanalyst needs to do to convert the Vigenère cipher into a Caesar cipher is know the length of the keyword.

To find the length of the keyword, look for a string of repeated text in the ciphertext (make sure it is longer than three letters). The distance between two equal repeated strings is likely to be a multiple of the length of the keyword. The distance is defined as the number of characters starting from the last letter of the first set of strings to the last letter of the second set of strings (e.g. “abcdefxyzxyzxyzabcdef” -> “abcdef” is repeated” -> distance is “xyzxyzxyzabcdef” which is 15 letters). The reason this works is that if there is a repeated string in the plaintext and the distance between these strings is a multiple of the keyword length, the keyword letters will line up and there will be repeated strings in the ciphertext also. If the distance is not a multiple of the keyword length, even if there is a repeated string of letters in the plaintext, the ciphertext will be completely different as the keyword would not match up and be different.

It is useful recording the distance between each set of repeated strings to find the greatest common factor. The number that factors the most into all of these distances (e.g. 6 is a factor of 6, 12, 18…) is most likely the length of the keyword. Once the length of the keyword is found, then every nth letter must have been encrypted using the same letter of the keyword. Thus, by recording every nth letter in one string, you can obtain what is essentially a Caesar cipher. The Caesar cipher is then attacked using frequency analysis. Once a few of these strings (of different positions on the ciphertext) are solved, the keyword can be revealed by checking the shift key against a tabula recta (e.g. if a certain string of nth letters is found to have been shifted 3 letters each, then the corresponding letter in the keyword must be “D”, which shifts every plaintext letter by 3 in the Vigenère cipher). When the keyword is deduced, every message encrypted using that keyword can now easily be decoded by you.

Although the Kasiski examination appears to be complex, attempting to try it reveals how simple the process is. Thus, it is useful to try encrypting a message using the Vigenère cipher then trying to work out the keyword using the Kasiski examination. Much like the frequency analysis, it is an extremely useful tool in the case of needing to break a secret code.

Posted in Science & Nature

Cryptography: Frequency Analysis

Posted on by Jinavie

A cipher is a message that has been encoded using a certain key. The most common and basic type of ciphers are encrypted using letter substitution, where each letter represents a different, respective letter. For example, the message may be encoded in a way so that each letter represents a letter three values before it on the alphabet (e.g. if a=0, b=1… “a” becomes “d”, “b” becomes “e” etc.). This creates a jumble of letters that appears to be indecipherable.

However, the characteristics of substitution ciphers make them the most decipherable type of encryptions. As each letter can only represent one other letter, as long as the key is cracked (i.e. what letter is what), the message and any future messages can be cracked. The most important tool in decrypting substitution ciphers is pattern recognition and frequency analysis.

Frequency analysis relies on the fact that every language has certain letters that are more used than others. In the English language, the letters that are most used, in order, are: E, T, A, O, I, N, S, H, R, D, L, U (realistically, only E, T, A, O are significant and the rest are neither reliable nor useful in frequency analysis).

For example, if Eve intercepted a long, encrypted message that she suspects to be a simple substitution cipher, she will first analyse the text for the most common letter, bigram (two letter sequence) and trigram. If she found that I is the most common single letter, XL the most common bigram and XLI the most common trigram, she can ascertain with considerable accuracy that I=e, X=t and L=h (“th” and “the” are the most common bigram and trigram respectively). Once she substitutes these letters into the cipher, she will soon discover that certain patterns arise. Eve may notice words such as “thCt” and deduce that C=a, or find familiar words and fill in the blanks in the key. The discovery of each letter leads to more patterns and the vicious cycle easily breaks the code.

Frequency analysis is extremely useful as it can be used to attack any simple substitution ciphers, even if they do not use letters. For example, in Sir Arthur Conan Doyle’s Sherlock Holmes tale The Adventure of the Dancing Men, Sherlock Holmes uses frequency analysis to interpret a cryptogram showing a string of hieroglyphs depicting dancing men.

To reinforce this weakness in substitution ciphers, many cryptographers have devised better encryption methods such as polyalphabetic substitution, where several alphabets are used (e.g. a grid of two alphabets – also called a tabula recta).

Posted in Psychology & Medicine

Process Of Elimination

Posted on by Jinavie

“How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?” ~ Sherlock Holmes

If there is not enough evidence to come to a conclusion of what is the truth, start by removing the possibilities that cannot be true. If you hack away these impossible answers one by one, you will ultimately end up with the truth. This method is highly useful in a multiple-choice type exam, where you cross off the false answers until only one remains (or take an educational guess from whatever remains). In medicine, a process of elimination can be used to narrow down a differential diagnosis, or to reach a diagnosis of exclusion – that is, a diagnosis that cannot be proven to be true but seems to be the only one that fits since all other diagnoses do not. 

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