Different types of ciphers besides Caesar Cipher?

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Different types of ciphers besides Caesar Cipher?

Post by ghostheadx2 on Mon May 18, 2015 11:57 pm
([msg=88108]see Different types of ciphers besides Caesar Cipher?[/msg])

I want to know a list of the different types of ciphers out there besides caesar. I need to know to be able to decrypt a message.
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Re: Different types of ciphers besides Caesar Cipher?

Post by ghost107 on Tue May 19, 2015 2:26 pm
([msg=88118]see Re: Different types of ciphers besides Caesar Cipher?[/msg])

  1. The substitution method:
    Similar to caesar cypher the substitution method is replacing every character in the alphabet with another character from the alphabet.
    Code: Select all
    A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
    Z I R A J S B K T C L U D M V E N W F O X G P Y H Q

  2. The mathematical Method of the caesar cypher:
    Same as the caesar cypher, every character is assigned a number and the encryption is C= (P+3) mod 26, this is a simple example, here you can apply many mathematical algorithms to shift the character.
    Code: Select all
    A B C D E F G H I J K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z
    0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

  3. Hill cypher
    Which also is a polygraph or block cypher. To avoid the vulnerability of the caesar and substitution, the Hill method divides the text into multiple blocks of the same length.

    Code: Select all
    THIS IS A MESSAGE


    Dividing the text message into small blocks of equal size(if the size of the last block is not even, fill the rest of the block with X):
    Code: Select all
    TH IS IS AM ES SA GE

    Replacing it with a number (the mathematical approach of the caesar cypher)
    Code: Select all
    {19, 7} {8, 18} {8, 18} {0, 12} {4, 18} {18, 0} {6, 4}


    For each element in the block we have a matrix A with same rows and columns as the block length.
    Code: Select all
        |x1   y1|
    A = |       |
        |x2   y2|


    The matrix A is applied to each block in the text, the bigger the block the complexer the encryption is.
    Code: Select all
    |C1|     |P1|
    |  | = A*|  |
    |C2|     |P2|


    To decrypt it you would need the inverse of A, instead of A:
  4. Transposition method:
    The transposition cypher is a much efficient method then the substitution, but it has a lot of disadvantages. The encrypted text has all the character from the initial text, but in a different order, uses a matrix of the order MxN where it interchanges the rows and columns to form a different matrix.

    Lets take the text the "This message uses the transposition method"(The example below only switched the rows)
    Code: Select all
      1 2 3 4 5 6 7          1 2 3 4 5 6 7
    1 T h i s m e s        3 s t h e t r a 
    2 s a g e u s e        4 n s p o s i t
    3 s t h e t r a        1 T h i s m e s
    4 n s p o s i t  =>    2 s a g e u s e
    5 i o n m e t h        6 o d x x x x x
    6 o d x x x x x        5 i o n m e t h
    7 x x x x x x x        7 x x x x x x x

  5. DES (Data Encryption Standard)
    Its kinda hard to explain but DES is a Feistel Cypher which processes blocks of 64 bits, creating encrypted blocks of 64 bits. The size of the secret key k is 56 bits, the input key is 64 bits, where 8 bits are used as parity bits(8, 16, 24, 32, 40, 48, 56, 64).

    - The encryption happens in 16 rounds, from the input Key K are generated 16 subkeys of 48 bits size(one key for each round)
    - Each round has 8 fixed substitutions
    - The text block of 64 bits is divided into two 32 bit sub-blocks
    Code: Select all
    IP -  Initial permutation (google it)
    E -  Expand, used to expand the block from 32 to 48 bits to apply the key
    S - Fixed substitutions, the function that applies the 8 fixed substitutions
    PC1, PC2 - Permuted Choice, a 56 bit permutation table
    Vi - circular left shifting on the i round(16 rounds vi = 1 when i = {1,2, 9,16}, vi = 2 in the rest)

    Key Generation Algorithm:
    - Apply PC1 to the Input key
    - Divide the result of the PC1 into two 28 bit (C0, D0)
    - For each subkey(ki) to generate (16 keys)
    Ci = Ci-1 <- vi
    Di = Di-1<-vi
    - The subkey is the result of the PC2, ki = PC2(Ci, Di)

    Algorithm:
    - Compute 16 subkeys from the input key
    - Use IP(text_block), and divide the result into two 32 bit blocks (L0, R0)
    - Run 16 rounds  for (Li, Ri), where i is a value from 1 to 16
    Li = Ri-1;
    Ri = Li-1 (+) f(Ri-1, Ki), where f(Ri-1, Ki) = P(S(E(Ri-1) (+) Ki))
    - Switching the final block( L16, R16) =>(R16, L16)
    - Applying the inverse of the IP to the final switched rounds(R16, L16), the result is the encrypted block



    Triple DES is a DES encryption with 3 keys
    Code: Select all
    Encrypt(Decrypt(Encrypt(text, k1), k2),k3)
    AES the functionality is similar to DES, to understand AES you must first understand how DES works.
You could also look into RC4, RC5, RC6.
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Re: Different types of ciphers besides Caesar Cipher?

Post by cyberdrain on Wed May 20, 2015 5:04 pm
([msg=88130]see Re: Different types of ciphers besides Caesar Cipher?[/msg])

Cryptool. It's a very useful program, but be sure to read through the documentation so you actually know how the program does its job.
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