Substitution

If we take the text "the quick brown" along with the cipher key of 3.

 

We can encrypt the text into "wkh txlfn eurzq".

 

The downside is that if we use the word "the" a lot, we'll also see "wkh" many times in the encrypted text. Using frequency analysis, a person could determine that "wkh" is equal to "the" and with that information decipher that the cipher key is "3". 

Tranposition

Transposition was later added to substitution to fix the problems introduced by substitution. A transpositional cipher works by making an anagram of the original text in a very specific way. 

 

Given  "wkh txlfn eurzq" (spaces included)

w k h |

t x l f

n | e u

u r q

if we go top down starting from the right, we get

" fuqhlerkx rwtnu"

Tranposition

By layering substitution and transposition on top of each other we fix the flaws from the previous cipher. 

 

A famous example of this is the "Engima" machine invented by the German to encrypt their messages against allied forces. 

 

This was eventually cracked by Alan Turing because the engima machine had a flaw where any character could not be encrypted into the original character it was. 

CBC

The initialization vector is the seed or "password key" used to start the encryption process. The password is added to the start of the text and becomes the first block of text to be encrypted.

 

The output of that encrypted block then becomes the input of the next block ensuring that consecutive instances of the word "the" is always encrypted to a different value each time.

 

With this technique, the wrong password would return a completely different output.

ASCII Example

This shows how manipulating the bits by just moving them left or right can completely change the output. This achieves both substitution and transposition based on how we move the bits around.

 

 

Hasing Functions

Hashing functions try to encrypt data by using a hash table to categorize data into unique outputs. 

 

Given a random number 16, a Hashing function that just runs modulus of 7 on the input would always return the value, 2. But 23 will also return the value 2.

 

A strong hashing function will aways return a unique output for any given input. 

Destructive Hashing

Some hashing functions are destructive in the sense that once a input is hashed, the original input value can never be "un-hash" from the output.

 

This can be very valuable for storing user passwords in a database. Paired with encrypting the password, the user password should be safe from decryption and unhashing even from the person that owns the application server.