Anybody please give examples of decoding cypher / codes using keys..?

Question

Mr. dontknow.. thanks for the detailed answer... I am particularly askng for examples,.. so please give the plain text for the cypher in your answer. or any other cypher and plaintext....I can understand better.. thanks one again..

Answer 1

Codes are usually called ciphers by 'professionals' or 'experts'.   Heres one:

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 plain

LST  UCL  KCL  GF  LST  DCL.     ciphertext message.

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

THE  CAT  SAT  ON  THE MAT.     ciphertext decoded back into plaintext.

The top line is the ordinary alphabet as we use it -called 'plaintext'  in the the science of cryptology (the study of ciphers/codes and how to create/break them).

The next line below is a small piece of coded message, which is called writing in 'ciphertext'. It is using a certain key, which has to be kept hidden to keep the message unreadable to intruders.

The third line is the key itself. The key here is really the whole line, but it is especially the word 'COUNTERSPY', because if you know this word, you know the whole cipher alphabet, since all the rest of the letters of the alphabet not used in this word 'counterspy' follow it in alphabetical order. (If you use a word with more than one letter the same as a keyword, then you only list each letter once. Eg if 'GREETINGS' was chosen as the keyword, it would become just GRETINS, and the whole key alphabet becomes GRETINSABCDFHJKLMOPQUVWXYZ).  

Finally the fourth line is the ciphertext decoded back into the original plaintext message.

As you can see, the first cipher letter in the cipher message is  L. To solve it, look at the key which uses COUNTERSPY as the keyword. L is the 20th letter in the key. So you look up the corresponding 20th letter in the plaintext -which is T. The next letter in the message is S, which is the 8th letter. So the corresponding 8th plaintext letter is H. You now have 'TH'. If you continue to do the whole message you should get a readable answer. In this case, the whole cipher message translates back into plaintext as THE CAT SAT ON THE MAT.

(Note: you will find it MUCH faster and easier to read off the corresponding letters if you write one alphabet directly above the other on a separate piece of paper, as my computer doesnt always accurately line them up, as you can see! You should always mark which alphabet is plaintext and which is ciphertext, because you can easily confuse yourself when using them).  

The above is an example of a simple substitution cipher, using a key word,  because you substitute one letter in plaintext for one letter of ciphertext. There is only one key in this example, so an A will always become a C, and vice versa, a C will always translate back into an A.

Codes/ciphers can be much more complicated, so that one letter can translate into several, etc etc., and there are different ways to employ keys.

Really there is not space here to cover them all, but you can get some good books on the subject. Eg: The Code Book, by Simon Singh. In his book, published in 1999, as well as covering all the main enciphering methods used throughout history, Simon held a competition for anyone to try to break 10 different kinds of ciphers, with prize money for the first person/s who did them all. They varied from easy to extremely difficult. The prize is now claimed, and was won about 1 or 2 years later by a Scandinavian team who pooled their efforts. But you can still try to solve them yourself for fun, and check up on his website how they were solved if youre stuck:

www.simonsingh.net/Crypto_Corner.html

Solving codes & ciphers requires a huge leap of faith that you can do it, and a lot of persistence and patience to keep going when you keep getting it wrong. But its also great fun; and when you do finally succeed, you cant beat the feeling it gives you!

Hope this helps with the basics.

Answer 2

The Zodiac Killer

Answer 3

a key is a computation method such  as genetic algorithms. It is not a machine with keys such as the enigma.

Answer 4

The one-time pad is extremely simple and is unbreakable, when used properly.

The key must be as long as the plaintext.

The USSR used it improperly: americans did brake it (see project VENONA).

Answer 5

Cool question and answers.  Thanks for asking it.

Answer 6

Enigma,in WW2.

Answer 7

read "The Golden Bug" by Edgar Allen Poe - a secret map is found and, guessing the language is English, they proceed thus: e is the most common letter/ the most common 3-letter word is "the" therefore the letters t and h are found....

Good story and not long.

Answer 8

Try this one.

The D’agapeyeff Cipher

    75628 28591 62916 48164 91748 58464 74748 28483 81638 18174

    74826 26475 83828 49175 74658 37575 75936 36565 81638 17585

    75756 46282 92857 46382 75748 38165 81848 56485 64858 56382

    72628 36281 81728 16463 75828 16483 63828 58163 63630 47481

    91918 46385 84656 48565 62946 26285 91859 17491 72756 46575

    71658 36264 74818 28462 82649 18193 65626 48484 91838 57491

    81657 27483 83858 28364 62726 26562 83759 27263 82827 27283

    82858 47582 81837 28462 82837 58164 75748 58162 92000