Cryptographs and Ciphers

Excerpts

• Cryptographs and Ciphers

  The art of constructing a cryptograph lies in the concealment of the proper order of the essential letters or words: the art of constructing a cipher lies in concealing what letters or words are represented by the symbols used.

• Cryptographs and Ciphers

  A simple example is when each letter is replaced by the one that immediately follows it in the natural order of the alphabet, *a* being replaced by *b*, *b* by *c*, and so on, and finally *z* by *a*.

• Cryptographs and Ciphers

  The majority of stories dealing with secret communications are concerned with the artfulness with which the message is concealed or conveyed and have nothing to do with cryptographs or ciphers.

• Cryptographs and Ciphers

  The defect of the method is that the broken letters at once attract attention and suggest the system used.

• Cryptographs and Ciphers

  It is said that during the Indian Mutiny messages in English, but written in Greek characters, were used freely, and successfully baffled the ingenuity of the enemy, into whose hands they fell.

• Cryptographs and Ciphers

  In English the letter which occurs most frequently is *e*.

• Cryptographs and Ciphers

  A cipher of the second type is one in which the same letter or word is, in some or all cases, represented by more than one symbol, and this symbol always represents the same letter or word.

• Cryptographs and Ciphers

  A disadvantage of this cipher is that since each letter is denoted by two symbols the length of the message is doubled by putting it in cipher.

• Cryptographs and Ciphers

  He took a key-word, such as *prudentia*, and constructed as many alphabets as there were letters in it, each alphabet being arranged cyclically and beginning respectively with the letters $p$, $r$, $u$, $d$, $e$, $n$, $t$, $i$, and $a$.

• Cryptographs and Ciphers

  cells, and each cell is determined uniquely by the two letters denoting its row and column.

• Cryptographs and Ciphers

  Lastly, no ambiguity should be possible in deciphering the communication.

• Cryptographs and Ciphers

  For twenty-four hours de Rohan pored over the message, but, failing to read it, he admitted his guilt, and was executed November 27, 1674.

• Cryptographs and Ciphers

  The Queen seems to have found writing in cipher a great trouble.

• Cryptographs and Ciphers

  A code dictionary is prepared in which every word likely to be used is printed, and the words are numbered consecutively $00000$, $00001, \ldots$ up, if necessary, to $99999$. Thus each word is represented by a number of five digits, and there are $10^5$ such numbers available.

• Cryptographs and Ciphers

  This is a cipher with $10^5$ symbols, and as each symbol consists of five digits, a message of $n$ words is denoted by $5n$ digits, and probably is not longer than the message when written in the ordinary way.

• Cryptographs and Ciphers

  If the clue number is the same all through the message it would be possible by not more than $10^5$ trials to discover the message.

• Cryptographs and Ciphers

  When a code message is published by the Government receiving it, the construction of the sentences is usually altered before publication, so that the key may not be discoverable by anyone in possession of the code-book or who has seen the cipher message.

• Cryptographs and Ciphers

  For if we make a similar code with the twenty-six letters of the alphabet instead of the ten digits, four letters for each word or phrase would give us $26^4$, that is, $456976$ possible variations.

• Cryptographs and Ciphers

  Poe wrote an essay on cryptography in which he said that it may be roundly asserted that human ingenuity cannot concoct a cipher which human ingenuity cannot resolve---a conclusion which is hardly justified by the known facts.

• Cryptographs and Ciphers

  More than one of his correspondents did not play the game fairly, not only employing foreign languages, but using several different ciphers in the same communication.

Equations

• Cryptographs and Ciphers

  10^5

  The five-digit code dictionary has 10^5 numbers available, one for each possible five-digit code word.

• Cryptographs and Ciphers

  26^4

  Four letters of the twenty-six-letter alphabet give 26^4 (456976) possible variations for each word or phrase.

• Cryptographs and Ciphers

  36^3

  Three symbols each chosen from the ten digits and the twenty-six letters give 36^3 (46656) possible words.

• Cryptographs and Ciphers

  5n

  A message of n words is written as 5n digits, since each word is represented by a five-digit number.

Problems

No exercises in this chapter.