Encryption Methods

[Man]

Locate the Encrypted Data
Your first task is to find the encrypted data. It might be cleverly concealed within a webpage, masquerading as something else, or it could be plainly visible but with the key or reference alphabet hidden.

Understand the Nature of the Crypt
Knowing what the crypt is supposed to reveal is crucial. Without this knowledge, decrypting it becomes significantly more challenging. Try to deduce what the decrypted output might be. It could range from simple text to an image, or even a binary program. If it's text, it might be something specific like mathematical formulas, coordinates, or just numbers. While there are numerous possibilities, typically only a few are logical.

Determine or Guess the Encryption Method
To successfully decrypt the cipher, you need to understand or at least have an educated guess about the encryption method used. The possibilities are vast. Start by investigating the person who created the encryption or the context in which the crypt was made for potential clues. A skilled cryptanalyst might be able to deduce the encryption method just from the crypt itself and could decrypt it using professional techniques, even without clear information. However, for most people, knowing the encryption method is a crucial part of the decryption process at some point.

Interpreting the Encrypted Message
Consider the word "hello." A basic form of encryption is to reverse it, resulting in "olleh." To an unsuspecting observer, this reversed text might seem like a foreign language: "?uoy era woh yeh." However, knowing that it's simply English in reverse, you can effortlessly decrypt it. There are numerous methods to encrypt text in such a way that it appears completely unrecognizable. If someone is aware of the encryption technique used, they can easily decrypt it to retrieve the original message. Let's explore some fundamental encryption methods:

1. Caesar cipher​

Simple cipher that shifts the alphabet by a number of letters. "abcdef" shifted by 2 becomes: "cdefgh". ROT-13 for example is a rotation of the alphabet by 13 letters. ROT-13 is so popular because there are 26 letters in the alphabet so its easy to encrypt it then encrypt it a second time to get it back to normal. You can write small programs to look for this kind of easy encryption (or just use rot13.com)

2. Mono-alphabetic substitution​

Replaces every letter with some other letter from the alphabet. No letter can be used twice of course. You will need a key that holds the mapping of the characters. The key has two parts. The first part is the original alphabet and the second part is the encryption key. Lets say "abcdef" is mapped to "fedcba". That means the word "beef" becomes "ebba". To crack those ciphers you will need to look for more frequent letters and words and guess the text... you will need a fairly large sample of ciphered text for it to work out. The word "the" for example is often used in the english language and "e" the most common letter. For other languages it will probably be different of course...

3. Vigenere cipher​

Every letter in the word gets shifted by a certain amount that is set by the password. This means the following... lets say the password is "bcde". Now say a=1 b=2 and so on... that means the first letter of the original text is shifted 2 letters, the second one is shifted by 3 letters and so on. This works great until you run out of the password characters. (It's only 4 characters long) Then you just start from the beginning again, in this case with "b" (=2). Notice how the A is converted to a number, here one (1) in the example. This is referencing by position. We talk about that later in more detail.

4. One time pad (with XORing)​

The most secure form of encryption is the one-time pad. It involves a lengthy sequence of random letters, known only to you and the person who will decrypt your message. You encrypt each letter of your original text using the corresponding letter from this random sequence. The outcome is a cipher that you transmit. The recipient, possessing the same one-time pad, can revert the cipher back to the original text using the pad's random letters. The challenge, however, lies in securely delivering the one-time pad to the recipient without it being intercepted and used by others to decrypt your message. Additionally, if multiple pads exist, the receiver must know which specific pad to use for decryption.

But how do you encrypt the two lines of letters together? The answer is to use the XOR (exclusive-or) operation. First, convert both strings to binary, a format consisting only of 0s and 1s. Each letter can be represented as a binary number, either using its ASCII code or an alphabetical numbering system (like A=1, B=2, etc.). Once converted to binary, you'll have a long string of 0s and 1s. Each set of binary digits (like an 8-bit code) corresponds to a specific letter, and you maintain this correspondence by not omitting leading zeros.

You then apply the XOR operation to these binary strings. In XOR, if one of the two bits is 1, the result is 1. If both bits are 0 or both are 1, the result is 0. This process effectively merges the two strings in a secure manner.

0 xor 0 = 0
0 xor 1 = 1
1 xor 0 = 1
1 xor 1 = 0

The resulting string can be decrypted by xoring with the known passkey (the one time pad you transmitted earlier to the other side), and then finally by converting to letters again by using either ASCII codes or alphabetic numbering. (Meaning: By referencing the position in a certain known alphabet).

Converting numbers to letters or vice versa​

In the examples provided, you may have noticed the transformation of letters into numbers and vice versa. This is typically achieved through a process of mapping letters to numbers. In computing, there are two main methods for this mapping. The first is the ASCII Table, which assigns a unique numerical code to every character, including letters, numbers, and special characters. You can easily learn more about ASCII with a quick online search. The second method is Unicode, which was developed as an extension to ASCII. ASCII is limited to 255 characters, which isn't sufficient for languages with extensive character sets, like Chinese. Unicode addresses this limitation, and more information can be found through a search engine.

Outside of computing, one can use a reference alphabet where each letter is mapped to a number based on its position in that alphabet. For example, in the alphabet "gcqlxebm", G would be 1, C would be 2, Q would be 3, and so on. Often, the natural sequence of "abcdefghijk..." is used due to its familiarity.

Another approach is to use hexadecimal (hex) numbers. Hex numbers include the letters A-F to represent the digits 10-15. This means that in certain cases, numbers can consist solely of letters. For those unfamiliar, hex numbers are based on a 16-base system, unlike our standard decimal system, which is based on 10.

Converting numbers to numbers​

While it might seem straightforward, the concept of changing number systems is crucial in cryptography. It's essential to remember that the appearance of data can be altered by converting it into a different number system. Our standard system is base ten, likely influenced by the fact that humans have ten fingers and toes. This principle allows for the transformation of a number into another base, rendering it virtually indecipherable to an attacker who is unaware of this change. A number in base 16 might appear similar to one in base 10, but its actual value is entirely different. Therefore, it's important to understand the base system you are dealing with.

For instance, if you encounter a large set of numbers where none exceed 3, it's likely that these numbers are in the base 4 system. In reality, the base system used could be any number. Determining the correct base system is a key part of understanding and working with such data in the field of cryptography.