Ciphers

Skip Code

The skip cipher is a transposition cipher that consists of extracting the letters of a message every n characters (by jumping n characters or skipping n−1). When the end of the message is reached, resume at the beginning (loop).

Encryption

for i in range(1, len(text)):
    start = (start + step) % len(text)
    cipher = cipher + text[start]

The Encryption and Decryption logic are same in the case of Skip Code.

Spartans Scytale

In cryptography, a scytale is a tool used to perform a transposition cipher, consisting of a cylinder with a strip of parchment wound around it on which is written a message. The ancient Greeks, and the Spartans in particular, are said to have used this cipher to communicate during military campaigns.

Encryption

cypher = ''
    text = split(text)
    output = np.array(text)
    output.resize(size, size)
    for i in range(0, size):
        for j in range(0, size):
            if output[i][j] == '':
                output[i][j] = '@'
    output = output.transpose()
    output = output.flatten()
    for letter in output:
        cypher += letter

Implementing a Scytale using a 2 dimensional array.

Rail Fence

Rail Fence Encryption uses an integer for the number of levels of the zigzag.The encoded message is written in zig-zag (like a rail fence/sawtooth) along a path with N levels/floors.

Encryption

if len(text) % 2 != 0:
    text += '@'
for letter in range(0, len(text)):
    if letter % 2 == 0:
        part1 += text[letter]
    else:
        part2 += text[letter]
text = part1 + part2

"@" is used as a filler value in this method.

Vigenere Cipher

The Vigenère cipher is a method of encrypting alphabetic text by using a series of interwoven Caesar.ciphers, based on the letters of a keyword. It employs a form of polyalphabetic substitution. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets . The encryption of the original text is done using the Vigenère square or Vigenère table.

Encryption

for i in range(len(string)):
    x = (ord(string[i]) +
         ord(key[i])) % 26
    x += ord('A')
    cipher_text.append(chr(x))

Caesar Cipher

Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet.

Encryption

keys = [x.upper() for x in keys]
for l in text:
    for i in range(0, 26):
        if l == letters[i]:
            cipher += keys[i]
    if l == ' ':
        cipher += ' '