74.
(Publisher: Wordware Publishing, Inc.)
Author(s): Gil Held
ISBN: 1556225989
Publication Date: 10/01/98
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The DRANDOM3.CPP Program
Listing 6.22 lists the statements in the program DRANDOM3.CPP, which represents the C++ version of DRANDOM3.BAS. Similar to previously described programs, both the source code and executable version of the program are stored in the C directory on the companion CD-ROM. The source file is named DRANDOM3.CPP and the executable file is named DRANDOM3.EXE.
In examining the program listing, note that although it is very similar to RANDOM3.CPP, it contains three new functions used to perform decryption operations. Those functions are decrypt, decryptKeyboardText, and decryptFile. The decrypt function performs the decryption of text based on the code used to generate a random number sequence. The decryptKeyboardText function writes text entered from the keyboard to an input file and decrypts the text to an output file. The third new function, decryptFile, performs the actual decryption of the contents of a file. The use of the executable version of DRANDOM.CPP should only be used with encrypted data generated by the executable version of RANDOM.CPP. This is because the BASIC language versions of those programs use a different random number generator, in effect precluding interoperability between the C++ and BASIC language versions of those programs.
Listing 6.22 The DRANDOM3.CPP program listing.
/* drandom3.cpp C++ code written by Jonathan Held, May 15, 1998, using Microsoft's Visual C++ version 5.0. */ //standard includes #include <iostream.h> #include <string.h> #include <stdlib.h> #include <iomanip.h> #include <fstream.h> //function prototypes void setupSeed(char *); void display(char *); void decrypt(ofstream, char []); void decryptKeyboardText(char *, char *); bool decryptFile(char *, char *); void formatData(char []); void getCode(char *&); void getFileNames(char * &, char * &); int getInputType(void); void groupBUFFER(ofstream, char [], int); //---------------------------------------------------------------- //Function: main() //Parameters: None //Return Type: int - 0 means program terminated normally, any other //value means abnormal termination //Purpose: Runs the main part of the program. //---------------------------------------------------------------- int main(){ char * the_Code, *infile, *outfile; int input_type; getCode(the_Code); setupSeed(the_Code); getFileNames(infile, outfile); input_type = getInputType(); //do something with file input first if (input_type){ decryptFile(infile, outfile); cin.get(); display(outfile); } else { decryptKeyboardText(infile, outfile); display(outfile); } return 0; }//end main() //---------------------------------------------------------------- //Function: display() //Parameters: name - the name of the file the user wants displayed //Return Type: None //Purpose: Echoes the resulting output file to the screen. //---------------------------------------------------------------- void display(char *name) { const int SIZE = 256; ifstream infile(name, ios::in); char input[SIZE]; cout << "Press return to display the encrypted file."; cin.getline(input, SIZE, '\n'); strcpy(input, input+strlen(input)); if (!(infile)){ cerr << "Unable to open input file for display." << endl; } else { while (infile.getline(input, SIZE, '\n')){ cout << input << endl; } } cout << endl; infile.close(); return; }//end display() //---------------------------------------------------------------- //Function: decrypt() //Parameters: wt - the output stream // text - the text that needs to be decrypted //Return Type: None //Purpose: Performs the decryption of the client's text based on //random numbers. //---------------------------------------------------------------- void decrypt(ofstream wt, char text[]){ const int SIZE = 256; char plaintext[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; int x, location, ix, jx; for (ix=0; ix < strlen(text); ix++){ x = (rand() % 26); for (jx=0; jx < strlen(plaintext); jx++){ if (text[ix] == plaintext[jx]) location = jx; } if (location < x) location += 26; text[ix] = plaintext[(location-x)%26]; } groupBUFFER(wt, text, strlen(text)); return; }//end encrypt() //---------------------------------------------------------------- //Function: decryptKeyboardText //Parameters: in - the input file name // op - the output file name //Return Type: None //Purpose: Writes the client's text to an input file and decrypts //it to an output file. //---------------------------------------------------------------- void decryptKeyboardText(char *in, char *op){ const int SIZE = 256; const int NEW_LINE = 92; char buffer[SIZE]; bool go_on = true; ofstream input(in, ios:: out); ofstream output(op, ios::out); if ((!input) || (!output)){ cerr << "Unable to open file " << in << " or " << op << "." << endl; } else { cout << "Enter the message in UPPERCASE or lowercase characters. " << endl << "Non-alphabetic characters may be entered but are ignored." << endl << "Use a / at the beginning of each line that should remain" << endl << "in plaintext and a \\ on a separate line to indicate the" << endl << "end of an enciphered message." << endl << endl; while (go_on){ cin.getline(buffer, SIZE, '\n'); input << buffer << endl; if (buffer[0] == '/'){ output << buffer << endl; } else if (((int) buffer[0]) == NEW_LINE){ go_on = false; } else { formatData(buffer); decrypt(output, buffer); } } } input.close(); output.close(); cout << "Plaintext saved in " << in << endl << "Encrypted text in " << op << endl << endl; return; }//end decryptKeyboardText() //---------------------------------------------------------------- //Function: decryptFile() //Parameters: inp - the input file name // op - the output file name //Return Type: bool indicating success of the operation //Purpose: decrypts the contents of a file. //---------------------------------------------------------------- bool decryptFile(char *inp, char *op){ const int SIZE = 256; char buffer[256]; bool success = false; //declare file stream objects ifstream input(inp, ios::in); ofstream output(op, ios::out); if ((!input) || (!output)){ cerr << "Unable to open/write to files " << inp << " or " << op << "." << endl; } else { success = true; while (input.getline(buffer, SIZE, '\n')){ if (buffer[0] == '/'){ output << buffer << endl; strcpy(buffer, buffer+strlen(buffer)); } else { formatData(buffer); decrypt(output, buffer); } } } input.close(); output.close(); return success; }//end decryptFile() //---------------------------------------------------------------- //Function: formatData() //Parameters: data - the array we want to format //Return Type: None //Purpose: Get rid of all spaces in the array. //---------------------------------------------------------------- void formatData(char data[]) { for (int mx=0, nx=0; (*(data+nx) != '\0'); nx++){ if (*(data+nx) == ' '){ //do nothing - skip over the space in the data } else { *(data+mx++) = *(data+nx); } } //don't forget to add the null terminator *(data+mx) = '\0'; return; }//end formatData() //---------------------------------------------------------------- //Function: getCode() //Parameters: the_Code - the code that will be entered by the client //Return Type: None //Purpose: Prompts the client for a keyword of at least six characters. //Checks the length of the keyword entered to make sure it has the //required number of characters. If it doesn't, it prints an error //message and prompts for a keyword again. //---------------------------------------------------------------- void getCode(char *&the_Code){ int length; bool go_on = true; char buffer[1000]; while(go_on){ cout << "Enter your secret code (6 characters minimum): "; cin >> buffer; length = strlen(buffer); if (length < 6) { cerr << "\aCode must be 6 characters or more!" << endl << endl; } else { the_Code = new char[length]; strcpy(the_Code, buffer); go_on = false; } } return; }//end getCode() //---------------------------------------------------------------- //Function: getFileNames() //Parameters: infile_name - the input file // outfile_name - the output file we will write the // enciphered text to //Return Type: None //Purpose: Get file information from the user. //---------------------------------------------------------------- void getFileNames(char * &infile_name, char * &outfile_name) { const int SIZE = 256; char data[SIZE]; cout << "Enter filename to store/retrieve plaintext message: "; cin >> data; infile_name = new char[strlen(data) + 1]; strcpy(infile_name, data); cout << "Enter filename to store enciphered message: "; cin >> data; outfile_name = new char[strlen(data) + 1]; strcpy(outfile_name, data); return; }//end getFileNames() //---------------------------------------------------------------- //Function: getInputType() //Parameters: None //Return Type: int - 0 indicates keyboard input, 1 indicates file // input //Purpose: Determines if the user will be manually entering text to //be enciphered or if the user wants a file to be enciphered. //---------------------------------------------------------------- int getInputType(void) { char type; bool error = false; int value; do { //prompt user for input from file or keyboard cout << "Is file input from keyboard (K, k) or file (F, f): "; cin >> type; //make type an uppercase letter type =static_cast<char>(toupper(static_cast<int>(type))); //check for an invalid character if ((type != 'K') && (type != 'F')){ cerr << "You have entered an invalid character!" << endl << endl; error = true; } else { if (type == 'K') value = 0; //value of 0 represents keyboard input else value = 1; //value of 1 represents file input error = false; } } while (error); cout << endl; return value; }//end getInputType() //---------------------------------------------------------------- //Function: groupBUFFER() //Parameters: out - the output stream we are writing to // num - the number of characters we want to output // buffer - the buffer to be written to the stream //Return Type: None //Purpose: Output the buffer in groups of five characters at a //time. //---------------------------------------------------------------- void groupBUFFER(ofstream out, char buffer[], int num) { for (int kx=0;kx<num;kx++){ if ((kx!=0) && (kx%25==0)){ out << endl; } if ((kx!=0) && (kx%5 == 0) && (kx%25!=0)){ out << " " << *(buffer+kx); } else { out << *(buffer+kx); } } out << endl; return; }//end groupBUFFER() //---------------------------------------------------------------- //Function: setupSeed() //Parameters: the_Code - a pointer to the keyword entered by the //client //Return Type: None //Purpose: Sets up the random number seed based on the keyword //code entered by the client. //---------------------------------------------------------------- void setupSeed(char *the_Code){ int seed = (int)*the_Code * (int)(*(the_Code+1)); int max = (int)(*(the_Code+2)) * (int)(*(the_Code+3)); float dummy; int increment; srand(seed); increment = (int) (*(the_Code + 4)); for (int ix=1; ix<max; ix+=increment) dummy = ((float) rand() )/RAND_MAX; max = (int)(*(the_Code + 4)) * (int) (*(the_Code+5)); for (int jx=1; jx<max; jx+=increment) dummy = ((float) rand() )/RAND_MAX; return; }//end setupSeed() //end file drandom3.cpp | Previous | Table of Contents | Next |
Learn Encryption Techniques with BASIC and C++
ISBN: 1556225989
EAN: 2147483647
EAN: 2147483647
Year: 2005
Pages: 92
Pages: 92
Authors: Gil Held