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user:asowers:secret_agent [2012/09/22 17:35] – created asowersuser:asowers:secret_agent [2012/09/24 17:08] (current) – [Code] asowers
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 +====Welcome Agent====
  
 +====Scope====
 +
 +This project will test your familiarity with more involved algorithms, storage, and control structures.
 +
 +Encoding is the process of converting a message into a coded form.
 +
 +Decoding is the reverse- retrieving that original message from an encoded form.
 +
 +In this project you will write a 2 programs: one that will take a plain text message and convert it into a coded form (largely indecipherable to the regular english expecting eye) using a given cipher key, and another that will reverse the process (or decipher), when given the appropriate key.
 +
 +The key is a numeric used to rotate the alphabet a set amount. Where A would normally equal 1, and Z 26, using a cipher key of 1 to shift 1 position to the right; A would now equal 2 (or B), B is now 3 (or C), and Z would be 1 (A).
 +
 +Your encoding program can operate as follows:
 +
 +obtains its cipher key from a text file called “key.txt”
 +or, if you prefer, use command-line arguments to provide the key
 +obtains the input message from a file called “plain.txt”
 +if “plain.txt” is blank, or does not exist, the program should prompt the user to enter the message via STDIN
 +outputs the ciphertext message to STDOUT AND saves it to a file called “cipher.txt”
 +implement error checking to avoid segfaults
 +The decoding operation is essentially the reverse (shifting to the left). I'd suspect you could reuse much of the same logic.
 +
 +Your decoding program:
 +
 +obtains its cipher key from a text file called “key.txt”
 +or, if you prefer, use command-line arguments to provide the key
 +obtains the input cipher from a file called “cipher.txt”
 +if “cipher.txt” is blank, or does not exist, the program should prompt the user to enter the message via STDIN
 +outputs the plaintext message to STDOUT AND saves it to a file called “plain.txt”
 +implement error checking to avoid segfaults
 +If you want, you may implement both functionalities into one program so long as you provide a mechanism for the user to access both operations (but note this is not required for successful completion of this project).
 +
 +====Code====
 +Encipher:
 +<code c>
 +/*
 + * encipher.c - program that encodes a message according to a key
 + *
 + *
 + * Compile with: gcc -o encipher encipher.c
 + *
 + * Place key value in: key.txt
 + * Place message to encipher in: plain.txt
 + * Enciphered message placed in: cipher.txt
 + *
 + * Execute with: ./encipher KEYVAL
 + *
 + */
 +#include <stdio.h>
 +#include <math.h>
 +#include <stdlib.h>
 +
 +int main(int argc, char **argv)
 +{
 +
 + printf("Greetings, Agent Haas.\n");
 + FILE *in, *out;
 +
 + int cipher;
 +
 + int key;
 +
 + in = fopen("plain.txt", "r");
 + out = fopen("enciphered.txt", "w");
 +
 + if(argv[1] == NULL)
 +
 + {
 +        printf("\nNo argument provided, execute with key argument.\nExample: ./encipher 1\n");
 +        exit(1);
 +    }
 +
 + char *plain;
 + plain = (char*) malloc (sizeof(char) * 127);
 + int count = 0;
 +
 + if(in == NULL)
 + {
 +        printf("\nFile empty, enter some text to encipher\n");
 +        fgets(plain, 127, stdin);
 +
 +        while(plain[count] != '\0')
 +        {
 +
 +        count = count+1;
 +        }
 +
 +        int cipher = atoi(argv[1]);
 +        count = 0;
 +
 +        while(plain[count] != '\0')
 +        {
 +            key = 1;
 +
 +            if(plain[count] >= 65 && plain[count] <= 90)
 +            {
 +                key = plain[count] + cipher;
 +
 +                while(key > 90)
 +                {
 +                    key = key - 26;
 +                }
 +            }
 +
 +            if(plain[count] >= 97 && plain[count] <= 122)
 +            {
 +                key = plain[count] + cipher;
 +
 +                 while(key > 122)
 +                {
 +                    key = key - 26;
 +                }
 +            }
 +            if(key == 1)
 +            {
 +                key = 32;
 +            }
 +
 +            fprintf(out, "%c", key);
 +            count = count+1;
 +        }
 +
 +        printf("\nEnciphered text is loated in enciphered.txt\n");
 + }
 +
 +    else
 + {
 +        fgets(plain, 127, in);
 +        printf("\nText before cipherication: ");
 +        while(plain[count] != '\0')
 +        {
 +        printf("%c", plain[count]);
 + count = count+1;
 +        }
 +        int cipher = atoi(argv[1]);
 +        count = 0;
 + printf("\nCiphered text output: ");
 +        while(plain[count] != '\0')
 +        {
 +            key = 1;
 + if(plain[count] >= 65 && plain[count] <= 90)
 +        {
 +                key = plain[count] + cipher;
 +                while(key > 90)
 +            {
 +                    key = key - 26;
 +            }
 +          }
 +
 +                if(plain[count] >= 97 && plain[count] <= 122)
 +      {
 +                key = plain[count] + cipher;
 +                while(key > 122)
 +                {
 +                key = key - 26;
 +                }
 +          }
 +                if(key == 1)
 +          {
 +                key = 32;
 +          }
 + printf("%c", key);
 + fprintf(out, "%c", key);
 + count = count+1;
 + }
 + printf("\nEnciphered text is located in enciphered.txt\n\n");
 + fclose(in);
 + fclose(out);
 +
 +     return (0);
 + }
 +}
 +</code>
 +Decipher:
 +<code c>
 +/*
 + * encipher.c - program that encodes a message according to a key
 + *
 + *
 + * Compile with: gcc -o encipher encipher.c
 + *
 + * Place key value in: key.txt
 + * Place message to encipher in: plain.txt
 + * Enciphered message placed in: cipher.txt
 + *
 + * Execute with: ./decipher KEYVAL
 + *
 + */
 +#include <stdio.h>
 +#include <math.h>
 +#include <stdlib.h>
 +
 +int main(int argc, char **argv)
 +{
 +
 +    FILE *in, *out;
 +    int key;
 +    in = fopen("enciphered.txt", "r");
 +    out = fopen("plain.txt", "w");
 +    if(argv[1] == NULL)
 +    {
 +        printf("Execute with key argument.\nExample: ./decipher 1\n");
 +        exit(1);
 +    }
 +    char *enciphered;
 +    enciphered = (char*)malloc(sizeof(char) * 127);
 +    int count = 0;
 +
 +    fgets(enciphered, 127, in);
 +
 +    printf("\nEnciphered text being deciphered: ");
 +
 +    while(*(enciphered+count) != '\0')
 +    {
 +        printf("%c", enciphered[count]);
 +        count = count+1;
 +    }
 +
 +    int cipher = atoi(argv[1]);
 +    count = 0;
 + printf("\nDeciphered text: ");
 +    while(enciphered[count] != '\0')
 +    {
 +        key = 1;
 + if(enciphered[count] >= 65 && enciphered[count] <= 90)
 +        {
 +            key = enciphered[count] - cipher;
 +
 +            while(key < 65)
 +            {
 +                key = key + 26;
 +            }
 +        }
 +
 +        if(enciphered[count] >= 97 && enciphered[count] <= 122)
 +        {
 +            key = enciphered[count] - cipher;
 +            while(key < 97)
 +            {
 +                key = key + 26;
 +            }
 +        }
 +        if(key == 1)
 +        {
 +            key = 32;
 +        }
 +        printf("%c", key);
 +        fprintf(out, "%c", key);
 +        count = count+1;
 +    }
 +    printf("\nDeciphered text wirtten to plain.txt\n\n");
 +
 +    fclose(in);
 +    fclose(out);
 +
 +    return (0);
 +}
 +</code>
 +<cli>
 +lab46:~/src/cprog/cipher$ ./encipher 1
 +Greetings, Agent Haas.
 +
 +Text before cipherication: Greeting Haas, reports suggest the Ocean is big. That is all.
 +
 +Ciphered text output: Hsffujoh Ibbt  sfqpsut tvhhftu uif Pdfbo jt cjh  Uibu jt bmm  
 +Enciphered text is located in enciphered.txt
 +
 +lab46:~/src/cprog/cipher$ ./decipher 1
 +
 +Enciphered text being deciphered: Hsffujoh Ibbt  sfqpsut tvhhftu uif Pdfbo jt cjh  Uibu jt bmm  
 +Deciphered text: Greeting Haas  reports suggest the Ocean is big  That is all  
 +Deciphered text wirtten to plain.txt
 +
 +lab46:~/src/cprog/cipher$ 
 +</cli>
 +
 +====After Thoughts====
 +This was a big jump from the previous project. This project properly demonstrated how to loop functions and preform mathematical functions while working with file I/O.
 +
 +====Sources====
 +Studying previous student examples proved imparitive in association with the following websites:
 +  - http://www.acm.uiuc.edu/webmonkeys/book/c_guide/1.2.html
 +  - http://www.asciitable.com/
 +  - http://cboard.cprogramming.com/c-programming/109142-caesar-cipher.html

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