Tag: sherlock

Posted in Psychology & Medicine

Three Types Of Responses

Posted on by Jinavie

In his book Praise of Escaping (“Éloge de la fuite”), physician Henri Laborit suggests the following. When a person faces an ordeal, they face three options. The first is to fight against the ordeal, the second is to do nothing and third is to flee from it.

Firstly, fighting against a challenge is a very natural behaviour. These people are not hurt by the ordeal because they turn the attack into a retaliation. But this attitude has a problem. Continuous attacks and retaliations result in a vicious cycle. An aggressive person ultimately will be stopped by someone who is stronger than them.

The second option involves not doing anything in the sense that you act as if you hadn’t been attacked by pushing down the resentment. This is the most widely accepted attitude in modern society. Scholars call this behavioural inhibition. People with this attitude have the want to punch their opponent in the face, but swallow their anger as they recognise the risk of being retaliated against and entering a vicious cycle. And so, the punch that did not land on the opponent hits themselves instead. This may even show as medical conditions such as stomach ulcers, aches, or other psychosomatic symptoms.

The third way of escaping can be done through different ways.
Chemical escape: Alcohol, cigarettes, drugs, stimulants, relaxants, sleeping pills. All of these can soften or erase the pain from external attacks. By using these substances to forget everything and knocking oneself out, the ordeal will pass. However, because this kind of escape weakens your sense of reality, people who use this method lose their ability to live in the real world.
Geographical escape: Moving from one place to another endlessly. Some people shift their problems by changing jobs, friends, lovers and the places they live in. It doesn’t necessarily solve the problem, but they feel a little better and gain energy from changing the environment they are in.
Creative escape: Transforming your anger and pain into film, music, writing, painting, sculpting etc. Some people take the things they cannot dare say in the real world and have characters in an imaginary world say it instead. By doing this, they feel a sense of catharsis. People who like to watch characters in movies and books take revenge against those who have wronged them also fit into this category.

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(from The Encyclopaedia of Relative and Absolute Knowledge by Bernard Werber)

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

How To Feign Death

Posted on by Jinavie

Usually to check if a person is dead, one checks their pulse and breathing. If you want to fake your death properly, you must be able to stop both of these. You can easily hold your breath, but how can one stop their own heart? The answer lies in a ball.

If you wedge a tennis ball, squash ball, baseball or any small but firm ball in each of your armpits and squeeze tightly, the pulse at your wrist will disappear. This pulse is the radial pulse, and the radial artery is a branch of the brachial artery further up the arm. If a ball is squeezed in the armpit, it compresses the brachial artery, stopping the blood flow to the radial artery and obliterating the radial pulse. Most people who are not medical professionals tend to use the radial pulse for taking a pulse, so this method can be used to make it look like you do not have a pulse. But as this trick only causes the radial pulse to disappear, it is ineffective if the other person takes the pulse at another site such as the carotid artery or femoral artery. However, if you can control the situation and the person checking to see if you are alive is not a doctor or nurse, then it is quite a useful trick to use.