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user:smalik2:portfolio:cprogproject1 [2012/02/25 01:37] – [Code] smalik2user:smalik2:portfolio:cprogproject1 [2012/02/28 22:30] (current) – [References] smalik2
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 +======Project: SECRET AGENT======
  
 +A project for C/C++ Programming by Saad Malik for SPRING 2012.
 +
 +This project was begun on 2/22/12 and is anticipated to take 2 days to complete. Project was completed on February 24, 2012.
 +
 +=====Objectives=====
 +Create a program that will encipher a message (make it unreadable).
 +
 +Create a second program that will take that unreadable message, and make it readable once again.
 +=====Prerequisites=====
 +In order to successfully accomplish/perform this project, the listed resources/experiences need to be consulted/achieved:
 +
 +  * successful completion of project #0 and solid understanding of pertinent topics
 +  * familiarity with memory allocation via **malloc(3)**
 +  * familiarity with looking up C function parameters/information in the manual
 +  * familiarity with if statements, especially in use for error detection
 +  * familiarity with pointers and pointer arithmetic
 +  * familiarity with loops
 +  * file I/O
 +
 +=====Background=====
 +
 +The purpose of this project is to write a program that will encipher, and a program to decipher, a message.
 +
 +This will basically involve the use of if blocks, looping, command line arguments, and sorting strings into arrays (and manipulating the data therein).
 +=====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 "message.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=====
 +
 +==The encipher code:==
 +
 +<code c>
 +#include <stdio.h>
 +#include <stdlib.h>
 +
 +//THIS PROGRAM WILL ENCIPHER A MESSAGE GIVEN A COMMAND LINE ARGUMENT
 +//THAT WILL BE USED AS THE ENCIPHERING KEY
 +
 +int main(int argc, char **argv)
 +{
 +        FILE *in, *out;
 +        int cipher;
 +
 +        long long int character;
 +
 +        in = fopen("plain.txt", "r");
 +        out = fopen("cipher.txt", "w");
 +
 +//This if block will check to make sure that the user entered a cipher key
 +//as an argument when they ran the program
 +
 +        if(*(argv+1) == NULL)
 +        {
 +                printf("\nERROR\n");
 +                printf("You did not provide an argument for the cipher key\n");
 +                printf("Please run the program again, with 1 integer argument that will be the cipher key\n");
 +                exit(1);
 +        }
 +
 +//This if block will ensure user does not enter an ungodly cipherkey
 +
 +        if(atoi(*(argv+1)) > 10000)
 +        {
 +                printf("\nPlease for the love of god enter a reasonable cipher key\n");
 +        exit(1);
 +        }
 +
 +
 +//This if block will allow the user to enter a message if the input file
 +//does not exist, else input the message from plain.txt.
 +//The message will also be ciphered and outputted to the cipher.txt and STDOUT.
 +
 +        char *message;
 +        message = (char*)malloc(sizeof(char) * 127);
 +        int count = 0;
 +
 +        if(in == NULL)
 +        {
 +                printf("\nPlease enter the message you want to encrypt\n");
 +                fgets(message, 127, stdin);
 +                printf("\nThe message that you want to encrypt is: \n");
 +
 +                while(*(message+count) != '\0')
 +                {
 +                        printf("%c", *(message+count));
 +                        count = count+1;
 +                }
 +
 +                int cipher = atoi(*(argv+1));
 +                count = 0;
 +
 +                printf("\nThe ciphered message is: \n");
 +                while(*(message+count) != '\0')
 +                {
 +                        character = 1;
 +
 +                        if(*(message+count) >= 65 && *(message+count) <= 90)
 +                        {
 +                                character = *(message+count) + cipher;
 +
 +                                while(character > 90)
 +                                {
 +                                        character = character - 26;
 +                                }
 +                        }
 +
 +                        if(*(message+count) >= 97 && *(message+count) <= 122)
 +                        {
 +                                character = *(message+count) + cipher;
 +
 +                                while(character > 122)
 +                                {
 +                                        character = character - 26;
 +                                }
 +                        }
 +                        if(character == 1)
 +                        {
 +                                character = 32;
 +                        }
 +
 +                        printf("%c", character);
 +                        fprintf(out, "%c", character);
 +                        count = count+1;
 +                }
 +
 +                printf("\nThe enciphered message is located in cipher.txt\n");
 +        }
 +
 +        else
 +        {
 +                fgets(message, 127, in);
 +
 +                printf("\nThe message that you want to encrypt is: \n");
 +
 +                while(*(message+count) != '\0')
 +                {
 +                        printf("%c", *(message+count));
 +                        count = count+1;
 +                }
 +
 +                int cipher = atoi(*(argv+1));
 +                count = 0;
 +
 +                printf("\nThe ciphered message is: \n");
 +                while(*(message+count) != '\0')
 +                {
 +                        character = 1;
 +
 +                        if(*(message+count) >= 65 && *(message+count) <= 90)
 +                        {
 +                                character = *(message+count) + cipher;
 +                                     while(character > 90)
 +                                {
 +                                        character = character - 26;
 +                                }
 +                        }
 +
 +                        if(*(message+count) >= 97 && *(message+count) <= 122)
 +                        {
 +                                character = *(message+count) + cipher;
 +
 +                                while(character > 122)
 +                                {
 +                                        character = character - 26;
 +                                }
 +                        }
 +                        if(character == 1)
 +                        {
 +                                character = 32;
 +                        }
 +
 +                        printf("%c", character);
 +                        fprintf(out, "%c", character);
 +                        count = count+1;
 +                }
 +
 +                printf("\nThe enciphered message is located in cipher.txt\n");
 +        }
 +        fclose(in);
 +        fclose(out);
 +
 +        return (0);
 +}                                                                                                                 
 +</code>
 +
 +==The decipher code:==
 +
 +<code c>
 +#include <stdio.h>
 +#include <stdlib.h>
 +
 +//THIS PROGRAM WILL TAKE A CIPHERED MESSAGE AND DECIPHER IT
 +//AS LONG AS YOU PROVIDE THE CORRECT COMMAND LINE ARGUMENT
 +//FOR A DECIPHER KEY
 +
 +int main(int argc, char **argv)
 +{
 +
 +        FILE *in, *out;
 +        int cipher;
 +
 +        long long int character;
 +
 +        in = fopen("cipher.txt", "r");
 +        out = fopen("plain.txt", "w");
 +
 +//This if block will check to make sure that the user entered a cipher key
 +//as an argument when they ran the program
 +
 +        if(*(argv+1) == NULL)
 +        {
 +                printf("\nERROR\n");
 +                printf("You did not provide an argument for the cipher key\n");
 +                printf("Please run the program again, with 1 integer argument that will be the cipher key\n");
 +                exit(1);
 +        }
 +
 +
 +//This if block will allow the user to enter a message if the input file
 +//does not exist, else input the message from plain.txt.
 +//The message will also be ciphered and outputted to the cipher.txt and STDOUT.
 +
 +        char *message;
 +        message = (char*)malloc(sizeof(char) * 127);
 +        int count = 0;
 +
 +        if(in == NULL)
 +        {
 +                printf("\nPlease enter the message you want to un-encrypt\n");
 +                fgets(message, 127, stdin);
 +                printf("\nThe message that you want to un-encrypt is: \n");
 +
 +                while(*(message+count) != '\0')
 +                {
 +                        printf("%c", *(message+count));
 +                        count = count+1;
 +                }
 +
 +                int cipher = atoi(*(argv+1));
 +                count = 0;
 +
 +                printf("\nThe un-ciphered message is: \n");
 +                while(*(message+count) != '\0')
 +                {
 +                        character = 1;
 +
 +                        if(*(message+count) >= 65 && *(message+count) <= 90)
 +                        {
 +                                character = *(message+count) - cipher;
 +
 +                                while(character < 65)
 +                                {
 +                                        character = character + 26;
 +                                }
 +                        }
 +
 +                        if(*(message+count) >= 97 && *(message+count) <= 122)
 +                        {
 +                                character = *(message+count) - cipher;
 +
 +                                while(character < 97)
 +                                {
 +                                        character = character + 26;
 +                                }
 +                        }
 +                        if(character == 1)
 +                        {
 +                                character = 32;
 +                        }
 +
 +                        printf("%c", character);
 +                        fprintf(out, "%c", character);
 +                        count = count+1;
 +                }
 +
 +                printf("\n");
 +        }
 +
 +        else
 +        {
 +                fgets(message, 127, in);
 +
 +                printf("\nThe message that you want to un-encrypt is: \n");
 +
 +                while(*(message+count) != '\0')
 +                {
 +                        printf("%c", *(message+count));
 +                        count = count+1;
 +                }
 +
 +                int cipher = atoi(*(argv+1));
 +                count = 0;
 +
 +                printf("\nThe un-ciphered message is: \n");
 +                while(*(message+count) != '\0')
 +                {
 +                        character = 1;
 +
 +                        if(*(message+count) >= 65 && *(message+count) <= 90)
 +                        {
 +                                character = *(message+count) - cipher;
 +
 +                                while(character < 65)
 +                                {
 +                                        character = character + 26;
 +                                }
 +                        }
 +
 +                        if(*(message+count) >= 97 && *(message+count) <= 122)
 +                        {
 +                                character = *(message+count) - cipher;
 +                                while(character < 97)
 +                                {
 +                                        character = character + 26;
 +                                }
 +                        }
 +                        if(character == 1)
 +                        {
 +                                character = 32;
 +                        }
 +
 +                        printf("%c", character);
 +                        fprintf(out, "%c", character);
 +                        count = count+1;
 +                }
 +                printf("\nThe un-enciphered message is located in plain.txt\n");
 +        }
 +        fclose(in);
 +        fclose(out);
 +
 +        return (0);
 +}
 +
 +</code>
 +=====Execution=====
 +This is the program running a cipher.  Without an argument, it gives you an error to rerun with an argument.
 +
 +It inputs the message from a txt file, and then enciphers it.  If the file doesn't exist, then it will prompt the user to enter a message.
 +
 +The enciphered message gets stored in cipher.txt.
 +
 +<cli>
 +lab46:~/src/cprog/Projects$ ./Project1
 +
 +ERROR
 +You did not provide an argument for the cipher key
 +Please run the program again, with 1 integer argument
 +lab46:~/src/cprog/Projects/Project1$ ./encipher 9183829183
 +
 +Please for the love of god enter a reasonable cipher key
 +lab46:~/src/cprog/Projects/Project1$ ./encipher 284
 +
 +The message that you want to encrypt is: 
 +Hello my name is Pastor John xyz XYZ  
 +The ciphered message is: 
 +Fcjjm kw lykc gq Nyqrmp Hmfl vwx VWX  
 +The enciphered message is located in cipher.txt
 +lab46:~/src/cprog/Projects/Project1$ 
 +
 +</cli>
 +
 +==DECIPHER==
 +
 +<cli>
 +lab46:~/src/cprog/Projects/Project1$ ./decipher
 +
 +ERROR
 +You did not provide an argument for the cipher key
 +Please run the program again, with 1 integer argument that will be the cipher key
 +lab46:~/src/cprog/Projects/Project1$ ./decipher 284
 +
 +The message that you want to un-encrypt is: 
 +Fcjjm kw lykc gq Nyqrmp Hmfl vwx VWX  
 +The un-ciphered message is: 
 +Hello my name is Pastor John xyz XYZ  
 +The un-enciphered message is located in plain.txt
 +lab46:~/src/cprog/Projects/Project1$ 
 +
 +</cli>
 +=====Reflection=====
 +The text files are created by the program, however if they do not exist the program does prompt the user to enter a message instead.
 +
 +Also, the program has checks in place in case the user does not enter a command line argument.
 +
 +This project really helped me fully understand how to manipulate strings of data, arrays, and command line arguments.  All the other concepts used I knew fairly well, but it strongly reinforced these three big ones and I can really appreciate that.
 +=====References=====
 +In performing this project, the following resources were referenced:
 +
 +http://www.asciitable.com/                          -- Helped deal with the ASCII aspect of the project.
 +
 +http://www.cprogramming.com/tutorial/lesson9.html   -- This webpage helped me make sense of how to handle strings in C.
 +
 +Matthew Haas also introduced the nice fgets and atoi functions.

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