Question

1. Cyphers are hundred of years old. Using pseudo code and the a substitution cypher write a function to decode the following message and give the expected solution for the this message

            IUHHKIN NAHKK KBNHT VUOYNG

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Answer 1

-> We can map each key of cypher text unit to its value.

-> After the mapping is done, we need to replace each character in cypher text with its mapped value, using the character as key.

->assume "Map" stores the mapping.

-> Map[key] = value assigns the charcter value to the key character.

-> Now we assign the above values:

key

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Algorithm to obtain message from cypher text:

// cypher_to_message will print the message text and take the mapping and cypher text as input

Cypher_to_message( Map, cypher_text )

{

  // len stores the length of cypeher text

  len = length_of (cypher_text);

// following line denotes that message text will also have length = len

message_text [ len ];

// for each index of message text we decide the which character is to be stored

// if we have mapping in Map for i^th character of cypher text then we assign its mapped value to

message_text[i]

// but if mapping is not present then message_text[ i ] will be equal to cypher_text[ i ]

  for each index i in range 0 to len-1:

{   

if ( we have mapping for cypher_text[ i ] )

   message_text [ i ] = Map[ cypher_text[ i ] ] ;

else

message_text [ i ] = cypher_text[ i ]  ;

}

print( message[text] );

}

For cypher_text = IUHHKIN NAHKK KBNHT VUOYNG

   message_text = THREE EXTRA POINTS