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| − | Cryptography is the process of hiding messages; either by concealing them (eg. hiding them in an image), or by obfuscating them outright (eg. substitution cipher).
| + | To learn about cryptography, check out the [http://gamedetectives.net/academy Game Detectives Academy] - a free, interactive series of tutorials! |
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| − | == Basic Terminology ==
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| − | * '''Cipher''': a method of encryption
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| − | * '''Plaintext''': the legible text of a hidden message
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| − | * '''Ciphertext''': the text after a message is concealed in it
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| − | * '''Encryption''': The process of turning plaintext into ciphertext
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| − | * '''Decryption''': The process of converting ciphertext back into plaintext
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| − | * '''Key''': a string used in the encryption and decryption processes of some ciphers, akin to a password
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| − | | |
| − | == Basic Ciphers ==
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| − | === Caesar cipher ===
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| − | ''Click [http://www.xarg.org/tools/caesar-cipher/ here] to experiment with the Caesar cipher.''
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| − | The simplest example of a cipher is the Caesar cipher. The rules of the cipher are as follows:
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| − | Let '''n''' equal a value from 1 to 25
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| − | Shift each letter in the plaintext forward by '''n''' positions in the alphabet
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| − | The resultant string is the ciphertext
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| − | For example, to encrypt the string <code>Game Detectives</code> using the Caesar cipher, using an arbitrary '''n''' value of 2, then:
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| − | G -> H -> I
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| − | a -> b -> c
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| − | m -> n -> o
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| − | e -> f -> g
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| − | ...
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| − | and the resultant ciphertext would be <code>Icog Fgvgevkxgu</code>. To decrypt this string back into <code>Game Detectives</code>, the process can simply be reversed by shifting each letter of the ciphertext 2 places backwards. (''Note: another common name for the Caesar cipher is ROT<n> - ROT13 indicates that each letter is shifted halfway through the alphabet)''
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| − | === Binary cipher ===
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| − | ''Click [http://www.binaryhexconverter.com/binary-to-ascii-text-converter here] to experiment with the binary cipher.''
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| − | '''What is binary?'''
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| − | Binary is a system of counting, used by computers, that is different than the typical system of counting. You're used to counting by using 10 different digits: 0 to 9. This is known as '''base 10''', or decimal. Binary only uses 2 digits: 0 and 1, so it is known as '''base 2'''. Let me give you an example.
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| − | This is how you write the number ''one hundred and nine'' normally, in base-10. The top row represents the values of each digit place; you can see that, starting from the right-hand side and moving left, each consecutive decimal place is worth '''10 times more''' than the previous one in '''base 10'''. The bottom row can use digits from 0 to 9.
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| − | +-----+-----+-----+
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| − | | 100 | 10 | 1 |
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| − | +-----+-----+-----+
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| − | | 1 | 0 | 9 |
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| − | +-----+-----+-----+
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| − | 1*100 + 0*10 + 9*1
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| − | = 100 + 0 + 9
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| − | = 109
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| − | Okay, now, here's how you write the same number, ''one hundred and nine,'' in base-2. Again, the top row represents the values of each digit place; but this time, each decimal place is only worth '''2 times more''' than the previous one in '''base 2'''. Now, the bottom row can only use the digits 0 and 1.
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| − | +-----+-----+-----+-----+-----+-----+-----+-----+
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| − | | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
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| − | +-----+-----+-----+-----+-----+-----+-----+-----+
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| − | | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
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| − | +-----+-----+-----+-----+-----+-----+-----+-----+
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| − | 0*128 + 1*64 + 1*32 + 0*16 + 1*8 + 1*4 + 0*2 + 1*1
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| − | = 0 + 64 + 32 + 0 + 8 + 4 + 0 + 1
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| − | = 109
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| − | So, the base-10 (decimal) number of 109 is equal to the base-2 (binary) number of 01101101.
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| − | '''How is binary used in a cipher?'''
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| − | The binary cipher relies on the fact that each ASCII character that you can type on your keyboard has a unique identifying code, in binary. For example,
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| − | * Uppercase <code>A</code> has a ASCII code, in binary, of <code>01000001</code> (converting to <code>65</code> in decimal)
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| − | * Lowercase <code>a</code> has a ASCII code, in binary, of <code>01100001</code> (converting to <code>97</code> in decimal)
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| − | * Ampersand <code>&</code> has a ASCII code, in binary, of <code>00100110</code> (converting to <code>38</code> in decimal)
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| − | * Plus sign <code>+</code> has a ASCII code, in binary, of <code>00101011</code> (converting to <code>43</code> in decimal)
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| − | So, all that is required to encrypt a binary cipher is to convert the ASCII characters into their codes - and to decrypt the cipher, the codes are changed into the characters. For instance, encoding the string <code>Game Detectives</code> would give you:
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| − | +-------+--------+
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| − | | ASCII | Binary |
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| − | +-------+--------+
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| − | | G |01000111|
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| − | | a |01100001|
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| − | | m |01101101|
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| − | | e |01100101|
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| − | | and so on... |
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| − | +-------+--------+
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| − | 01000111 01100001 01101101 01100101 00100000 01000100 01100101 01110100 01100101 01100011 01110100 01101001 01110110 01100101 01110011
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