Attacks on Encryption

 Background.  Encryption is the process of transforming plaintext or standard language into a much less easily decipherable ciphertext using a specific technique, process and/or algorithm. For example, take the phrase Some people claim this is a decipherable phrase. We can transform this into a variety of other phrases based on a huge variety of different approaches.  We will illustrate a few simpler transformations.  The first is fairly simple and associates each letter of the alphabet with another letter of the alphabet as shown in the following table.

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

 Transforming the original phrase using this code gives the following phrase Cern dnedfn kflpr bhpc pc l jnkpdhnulmfn dhucn. Notice I have retained the word structure, which unfortunately should help someone trying to decipher the code.  For example, the letter l is likeliest to represent either an a or an i because it appears as a single letter word. But we can develop an easier code using the next table.

 Original Letter 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 Code 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 26

 Transforming the original phrase using this code gives the following phrase19 15 13 5 16 5 15 16 12 5 3 12 1 9 13 20 8 9 19 9 19 1 4 5 3 9 16 8 5 18 1 2 12 5 16 8 18 1 19 5 Which replaces the following string of letters. S  O  M  E P  E O  P  L  E C L A I M  T H I S  I S  A D E C I P H E R A B L E P H R A S E Notice I have not retained the word structure, which makes it a little bit harder to decrypt.  But this encoding is likely to be one of the first that anyone trying to decrypt the phrase will try. I can complicate this code just a bit by shifting the numbers four to the left.  This gives the following table.

 Original Letter 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 Code 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 1 2 3 4

 This complicates the options that a decrypter must consider.  You can think of the number of cells that the code is shifted as a key relative to this particular type of encryption.  So you can see for shifting the code sequence to the left we could have 25 different keys.  These would have their equivalents for shifting to the right.While it is true that most encryption processes seem to make use of a key, not all do.  And while a key may be used, there are still a huge variety of different strategies that can be used even with a key. So, even with these very simple codes you should be able to see that attacks on encryption are likely to require a much more sophisticated attacker. We will talk in much greater depth about encryption in later weeks. More will be added.