Ciphers for spies in .NET Embed ANSI/AIM Code 128 in .NET Ciphers for spies

How to generate, print barcode using .NET, Java sdk library control with example project source code free download:
Ciphers for spies use visual studio .net code 128a integrated toaccess code-128c for .net Code11 Example 7.6 Encipher the message AGENTXFOURXREPORTSXTHATXCONVOYXLEFTXGLASGOWXTODAYX using garbo s seco Code 128 for .NET nd cipher with substitution box as above and the 12long transposition 6 1 10 4 8 11 3 7 12 2 9 5 The message date is Tuesday 18th of May..

Encipherment We write the messa visual .net Code 128 Code Set C ge out in 5-letter groups:. AGENT XFOUR XREPO RTSXT HATXC ONVOY XLEFT GLASG OWXTO DAYXX (an extra X has be VS .NET barcode 128 en added at the end to complete the last group). The substitution box is as in Table 7.

5. The substituted text, using the rules above, is therefore. VFDOT QIEYR QTDMO IDYWT GCPWC XLACY QADGT NAIQG XXORO ECNWX The transposition key is 6 1 10 4 8 11 3 7 12 2 9 5 Table 7.6 6 1 10 4 8 11 3 7 12 2 9 5. F M X I X D O L Q O I A G T D C X Q Y Y X I W Q O E T A R Y G D O R C G E Q P T C T W N N V D C A W and since the mont barcode standards 128 for .NET h of the transmission is May we must begin entering the text under the column headed 5: see Table 7.6.

The text is now taken out column by column starting with the column numbered 1:. DOLQQ PTCET ARTDC XVDCA WFMXI XYGDO QYYXT WNNOI AGIWQ ORCGE. chapter 7 Table 7.7 6 1 10 4 8 11 3 7 12 2 9 5. T C Q I C A Y W E W Y Q T F X O A M T R R X W C D T I N G O D X N E L C Y O Q X G I Q V D A P D O G We now use the tra nsposition box again. Since the day of transmission is Tuesday (the date is irrelevant in this simpli ed form of garbo s cipher) we begin writing the text under the column headed 3: see Table 7.7.

Finally, we take the text out column by column, starting with the column numbered 1, and write it out in ve-letter groups ready for transmission:. CAYWQ XGIDT INGTF XOPDO GTCQI ODXNE AMTRQ VDAEW YQRXW CLCYO. Decipherment in th is system is a tedious process in which it is easy to make mistakes. To begin the decipherment the receiver has to work out, from the day of the week and the length of the message, which columns of the transposition box will have an extra letter and which they are. In the example above since the message contains 50 characters there will be 10 columns of 4 letters and 2 columns of 5 letters.

Since the day of the week is Tuesday ( 3) the columns headed 3 and 7 will be the long columns and the others will be short . The same analysis will have to be used when the transposition is used again; in this case the month is May ( 5) so the long columns will be those headed 5 and 6 (since the column headed 6 happens to follow the column headed 5 ). For more details of garbo s cipher systems see [7.

1].. One-time pad The basic weakness of the book cipher as used above is that both the message and the key were in English and by dragging cribs based upon common English words which might occur in either we were able to recover both. Had the key not been in English, decryption would certainly have been more dif cult for the cryptanalyst but the messages would nevertheless be read eventually once he had discovered that this was the case, since cribs from the other language could also be used. If, on the other hand, the key was not based upon a natural language but was.

Ciphers for spies simply a random string of letters, taken from a page of random letters which is destroyed after use so that it can never be used again, then we have what is known as a one-time pad and the resulting cipher cannot be solved. This may seem to be a very bold assertion, but it is a mathematical fact [M7]. Since one-time pads provide total security why are they not used for all encipherments Basically because a different pad has to be provided for every pair of people who need to communicate, each of whom has one of the only two copies produced, and although this is feasible for a few hundred pairs, such as ambassadors communicating with their governments, it is out of the question for large numbers of military units in wartime.

It must also be realised that the situation changes dramatically if a one-time pad is used more than once. We then have a depth of two, or more, cipher messages enciphered with the same additive key. By subtracting one text from another the key is eliminated and the resulting differenced text is now the difference of two unenciphered texts and a crib-dragging or similar technique may lead to their decryption.

If a one-time pad is used to encipher code groups, rather than natural language, the cryptanalyst s task is much harder since he must have some knowledge of the code itself in order to use the crib-dragging attack, but the method is essentially the same. For a variety of reasons, including the provision of one-time pads, cryptographers are very interested in methods by which random letters (or numbers) can be generated. We look at some of the methods of doing this in the next chapter.

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