+ Reply to Thread
Results 1 to 2 of 2

Thread: Cryptanalysis 101

  1. #1
    Nitefyre's Avatar
    Nitefyre is offline Super Moderator TwelevePlus
    Tweleve Cleric
    Gold
    Nitefyre is on a distinguished road
    Join Date
    Feb 2005
    Location
    In my head
    Posts
    403

    Default Cryptanalysis 101

    Bear with me, this is my first one!  To start, I better explain why we aren’t reading up on cryptology and studying cryptanalysis instead.  Technically cryptology is the study of encrypting messages into a form only readable by the person who holds the key.  Cryptanalysis is the study of breaking the encryption and being able to read the message.  In most cases we will not be given the key or the key is hidden from us, by applying cryptanalysis we can either reveal the message or gain further insight into what the key may look like.  Either way we succeed in reading the message.  A message that hasn’t been decoded and is in readable form is referred to as plaintext while the encrypted message form is called ciphertext.  The ciphertext is the form we will be studying to search for recognizable patterns and help in deciding what sort of encryption or cipher is being used.  A cipher is the process of encrypting a message.

    The focus of our study and the most basic encryption forms are the simple substitution ciphers.  These ciphers use a symbol, number or another letter to replace a single letter in the message.  That symbol, number or letter is a constant throughout the cipher and will not change.  For example if the plaintext 'E' = the ciphertext 'Y', every Y throughout the ciphertext will represent the E, always.  I will first introduce the most easily recognized ciphers so if one happens to cross your path, you already have the key and do not need to waste the time trying to crack it.  After that we will be looking at the methods to deciphering and cracking simple substitution ciphers.

    The common substitution ciphers that replace a one letter for another letter are the shift cipher (also called the caeser cipher,) Atbash cipher, and the mixed alphabet cipher.  The shift cipher simply translates the cipher alphabet any number of spaces to the right (shift of one to tweny-six.)  Here is an example of a shift cipher by using the key 'shift of two':

    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      = plaintext
    Y  Z  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X      = ciphertext

    which turns the phrase 'this is fun' into 'rigq gq dsl'

    An Atbash reverses the ciphertext alphabet, looking like this:

    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     = plaintext
    Z  Y  X  W V  U  T  S  R Q  P O  N  M  L  K  J  I  H  G  F  E  D  C  B  A     = ciphertext

    turning the phrase 'this is fun' into 'gsrh rh ufm'

    The mixed alphabet cipher takes it one step further, usually using no or a very sporadic pattern in assigning letters.  This type of cipher can be commonly found in your Sunday paper's cryptograms or cryptoquotes.  A mixed alphabet cipher will look similar to this:

    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 = plaintext
    H F Y U I Z D A R W M V B P C E J X G L N K O Q S T = ciphetext



    *To be continued....*

  2. #2
    pianoman's Avatar
    pianoman is offline Expert Twelever TwelevePlus
    Peridot
    pianoman will become famous soon enough
    Join Date
    Apr 2007
    Posts
    1,382

    Default

    Quote Originally Posted by Nitefyre View Post
    A ÂquackB ÂquackC ÂquackD ÂquackE ÂquackF ÂquackG ÂquackH ÂquackI ÂquackJ ÂquackK ÂquackL ÂquackM ÂquackN ÂquackO ÂquackP ÂquackQ ÂquackR ÂquackS ÂquackT ÂquackU ÂquackV ÂquackW ÂquackX ÂquackY ÂquackZ Âquack Âquack Âquack= plaintext
    Y ÂquackZ ÂquackA ÂquackB ÂquackC ÂquackD ÂquackE ÂquackF ÂquackG ÂquackH ÂquackI ÂquackJ ÂquackK ÂquackL ÂquackM ÂquackN ÂquackO ÂquackP ÂquackQ ÂquackR ÂquackS ÂquackT ÂquackU ÂquackV ÂquackW ÂquackX Âquack Âquack Âquack= ciphertext

    which turns the phrase 'this is fun' into 'rigq gq dsl'
    LOL!
    This really did turn out to be quite fun!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts