A project for C/C++ by Josh Davis during the Spring 2012.

This project was begun on 2/14/2012 and is anticipated to take 2.5 Decades to complete. Project was completed on MONTH DAY, YEAR.

To write a program that depending on what it is asked to do will either cipher or decipher a message.

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

Thought the above listed are what are required… My unorthodox approach to completing stuff seemed to lead me in a direction that was slight variations of this.

Green with a blue border?

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).

Note: since the odd way I wrote my Cipher it changed the way that worked in relation to this, but the decipher is that of which was asked.

The encipher code: Original cipher (Not the one that was meant to be wrote)

  1 /*
  2  * encipher.c - program that encodes a message according to a key
  3  *
  4  *
  5  * Compile with: gcc -o encipher encipher.c
  6  *
  7  * Place key value in: key.txt
  8  * Place message to encipher in: plain.txt
  9  * Enciphered message placed in: cipher.txt
 10  *
 11  * Execute with: ./encipher    or    ./encipher KEYVAL
 12  *
 13  */
 14
 15 #include <stdio.h>
 16 #include <stdlib.h>
 17 int main(int argc, char **argv)
 18 {
 19         // File Info for input and output
 20         FILE *out,*out1;
 21 //        char value = 0;
 22 //        in=fopen("message.txt", "r");
 23 //      fscanf(in, "%c", &value);
 24         out=fopen("cipher.txt", "w");
 25         out1=fopen("key.txt","w");
 26 //        char *input, *pick;
 27 //        input=(char *)malloc(sizeof(char)*1);
 28 //        pick=(char *)malloc(sizeof(char)*1);
 29 //        *input=0;
 30 //        *pick=0;
 31         int key =0;
 32         unsigned char i;
 33         unsigned char q;
 34         char len=0,x,pos=0;
 35 //      printf("your program is broke\n");
 36         if(argc<2)
 37         {
 38                 printf("%8s must be run with 1 or\
 39                 more arguements, you only provided %hhu\n",*(argv+0),(argc-1));
 40                 exit(1);
 41         }
 42         printf("please enter a value in which you feel safe:\n");
 43         scanf("%d",&key);
 44         fprintf(out1, "%d",key);
 45 //        printf("you ran this program with %hhu arguments, they are:\n", argc);
 46         printf("your secret is safe with me:\n");
 47
 48         for(i=1; i<argc; i++)
 49         {
 50                 pos=0;
 51                 len=0;
 52 //              printf("testa\n");
 53                 x=*(*(argv+i)+pos);
 54                 fprintf(out, " ");
 55                 while(x!='\0')
 56                 {
 57                         len++;
 58                         pos++;
 59                         printf("%c", x+1);
 60                         fprintf(out,"%c", x+key);
 61                         x=*(*(argv+i)+pos);
 62                 }
 63 //              printf("\nthis ones for matt\n");
 64         //      for(pos=0;pos!=len+1;pos++)
 65         //      {
 66         //              printf("test b\n");
 67         //              printf("%c", *(*(argv+pos))+1);
 68         //      }
 69
 70                 printf(" ");
 71 //              for(q=0; q<argc; q++)
 72 //              {
 73 //
 74 //                      printf("%c",*(*(argv+i)+q)+1);
 75 //              }
 76 //              printf("\n");
 77         }
 78 //      fprintf(out,"\n -1");
 79 //      fclose(in);
 80         fclose(out);
 81         return(0);
 82 }
 83
 

NEW CIPHER

  1 #include<stdio.h>
  2 #include<stdlib.h>
  3
  4 int main()
  5 {
  6         FILE *in,*out,*key;
  7         char c, fname[] = "cipher.txt";
  8 //      value = (char*)malloc(sizeof(char) * 250);
  9         char keyx =0;
 10 //      char x =0;
 11         key=fopen("key.txt", "r");
 12         in=fopen("plain.txt", "r");
 13         out=fopen("cipher.txt", "w");
 14         if (in == NULL)
 15         {
 16                 printf("ERROR!\n");
 17                 exit(1);
 18         }
 19 //        fgets(value, 250, in);
 20         fscanf(key, "%hhd", &keyx);
 21 //        while(*value != EOF)
 22 //      {
 23 //                printf("original values are %hhd,  ", value);
 24 //                x=(value-keyx);
 25 //                fprintf(out,"%hhd", x);
 26 //                printf("new value is %c", value);
 27 //                fscanf(in, "%hhd", &value);
 28 //      }               c = fgetc(in);
 29         c = fgetc(in);
 30         while(c != EOF)
 31         {
 32                 if((c >= 65) && (c <= 'Z'))
 33                         c = c + keyx;
 34                 else if((c >= 'a') && (c <= 'z'))
 35                         c = c + keyx;
 36
 37                 if((c == ('Z' + 1)) || (c == ('z' + 1)))
 38                         c = c + keyx;
 39
 40                 fprintf(out, "%c", c);
 41                 fprintf(stdout, "%c", c);
 42
 43                 c = fgetc(in);
 44         }
 45         printf("\n");
 46         fclose(in);
 47         fclose(key);
 48         fclose(out);
 49         return(0);
 50 }
 51

Decipher code

  1 #include<stdio.h>
  2 #include<stdlib.h>
  3
  4 int main()
  5 {
  6         FILE *in,*out,*key;
  7         char c, fname[] = "cipher.txt";
  8 //      value = (char*)malloc(sizeof(char) * 250);
  9         char keyx =0;
 10 //      char x =0;
 11         key=fopen("key.txt", "r");
 12         in=fopen("cipher.txt", "r");
 13         out=fopen("message.txt", "w");
 14         if (in == NULL)
 15         {
 16                 printf("ERROR!\n");
 17                 exit(1);
 18         }
 19 //        fgets(value, 250, in);
 20         fscanf(key, "%hhd", &keyx);
 21 //        while(*value != EOF)
 22 //      {
 23 //                printf("original values are %hhd,  ", value);
 24 //                x=(value-keyx);
 25 //                fprintf(out,"%hhd", x);
 26 //                printf("new value is %c", value);
 27 //                fscanf(in, "%hhd", &value);
 28 //      }               c = fgetc(in);
 29         c = fgetc(in);
 30         while(c != EOF)
 31         {
 32                 if((c >= 65) && (c <= 'Z'))
 33                         c = c - keyx;
 34                 else if((c >= 'a') && (c <= 'z'))
 35                         c = c - keyx;
 36
 37                 if((c == ('Z' + 1)) || (c == ('z' + 1)))
 38                         c = c - keyx;
 39
 40                 fprintf(out, "%c", c);
 41                 fprintf(stdout, "%c", c);
 42
 43                 c = fgetc(in);
 44         }
 45         printf("\n");
 46         fclose(in);
 47         fclose(key);
 48         fclose(out);
 49         return(0);
 50 }

jdavis34@lab46:~/src/cprog$ ./cipher This works finally because matt put up that hint thank you matt
please enter a value in which you feel safe:
2
your secret is safe with me:
Vjku yqtmu hkpcnn{ dgecwug ocvv rwv wr vjcv jkpv vjcpm {qw ocvv
jdavis34@lab46:~/src/cprog$ ./decipher
 This works finally because matt put up that hint thank you matt
jdavis34@lab46:~/src/cprog$

2nd revision of the more intended main cipher(cipher2)

jdavis34@lab46:~/src/cprog$ echo key.txt > 2
jdavis34@lab46:~/src/cprog$ ./cipher2
Vjku oguucig ku c vguv vq ugg kh vjku yknn yqtm

jdavis34@lab46:~/src/cprog$ ./decipher
This message is a test to see if this will work

Comments/thoughts generated through performing the project, observations made, analysis rendered, conclusions wrought. What did you learn from doing this project?

In performing this project, the following resources were referenced:

• Matt?
• Jpettie? the PAlly
• Hint.c ( help with the fgetc vs using the fscanf or fgets)