Secret message in .NET Creation Code 128C in .NET Secret message

Secret message using .net vs 2010 toproduce uss code 128 for web,windows application Microsoft .NET Compact Framework If we take the Visual Studio .NET Code 128 rst letter of the message and the rst letter of every fourth word after that, taking hyphenated words as two separate words, we get. ATTACKDUEONTHIRD [72]. Ciphers for spies Stencil ciphers The example abov e is a very simple, and insecure, case of a stencil cipher. In such a cipher certain letters on a page are part of the secret message and all the other letters are merely llers which are used to compose a mundane-looking communication. The stencil in the example is far too regular to be satisfactory; a more suitable stencil would use letters which are separated from each other by irregular intervals and which are not necessarily the rst letters of words.

To add further security the letters of the secret text would probably not occur in their correct order in the overall text. If the overall text is typed in a regular format the sender and recipient may have identical cards with holes punched in them at the positions of the letters of the secret message. Hence the name of this type of cipher.

Each hole would have a number underneath it giving the position of its corresponding letter in the message. Such a cipher would be much harder to solve unless the same stencil was used repeatedly in which case, given enough messages, it might be possible for a cryptanalyst to recover part of the stencil and from that gradually to recover the rest. If, however, the stencil changed regularly it would be extremely dif cult, if not impossible without further information, to solve the system.

To get some idea of the dif culty consider this. Example 7.2 (stencil cipher) Text of message:.

Some of Shakespe code128b for .NET are s plays such as SSSS 10SSSS 6SSSSSSSSS SSSSSS 8SS 1 Anthony and Cleopatra are performed SS2SSSS S SSSS9SSS3SS SSS SS 11 15 SSS7 less frequently than others, Macbeth SSSS SSSSSSS S SS4S SSSSSS SSS5SSS 12S 13 King Lear and Hamlet, in particular. S S SSSS SS 14S 16.

The numbers show where the holes in the stencil were placed and give the order in which the visible letters are to be read; where a two-digit number is needed the letter above the rst digit is the one where the hole occurs; the letter has been underlined for clarity, though of course it would not. chapter 7 have been underl ined in the message as sent! Thus the message reads, after insertion of spaces,. ATTACK DUE ON THIRD as before. If a stencil is used several times it might be possible for a cryptanalyst to discover where the holes are placed, and in what order they are used, but it would depend on whether any likely plaintext phrases or words were available and on the number and length of the messages. If the stencil was changed after every page it would be impossible to read the messages unless there was some relationship between the make-up of a message stencil and its successor, for without knowing the stencil many possible messages might be found within a page as is illustrated by Problem 7.

1 Verify that all but one of the following messages can be found within the text of the example above and so are possible solutions given an appropriate stencil:. (1) (2) (3) (4). MERRY CHRISTMAS; COME AT ONCE; GO AWAY QUICKLY; THE AUTHOR OF OTHELLO IS BACON. Hundreds of othe Visual Studio .NET ANSI/AIM Code 128 r possible solutions could be found within the text since it contains over a hundred letters and any anagram of any subset could be picked out with an appropriate stencil. Without further information such as, for example, that a stencil will not have more than one hole in any row or column, such a message is unbreakable since many solutions are possible.

The same situation can apply to other cipher systems where insuf cient material is available to provide a unique solution. Even a simple substitution system is unbreakable if it is used only once for a single short message. In the extreme case of a one-time pad the system is unbreakable no matter how many messages of any lengths are sent, as we shall see later.

If the same system (simple substitution, transposition, stencil) is used more than once it may cease to be unbreakable ; even a one-time pad may lose its security if the same pad is used twice..
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