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otp_dec_d.c
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/*************************************************************************************
* Author: Mae LaPresta
* Title: otp_dec_d.c
* Description: Communicates with opt_dec, gets sent an encoded message and the key
* used to encode the message. Decodes the message with the given key,
* and returns the decoded message.
*************************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
void error(const char *msg) { perror(msg); exit(1); }
int main(int argc, char *argv[])
{
int listenSocketFD, establishedConnectionFD, portNumber, charsRead, charsWritten;
socklen_t sizeOfClientInfo;
int numChildren = 0;
int i;
char buffer[1000];
char totalMsg[70000];
char totalKey[70000];
char decodedMsg[70000];
char clientID[4];
char verifyID[]="dec";
char ready[]="OK";
char refuse[]="NO";
uint32_t msgLength;
uint32_t msgLength_beforeConvert;
pid_t activeSpawn[5]={-5};
struct sockaddr_in serverAddress, clientAddress;
int charsRecCount;
if (argc < 2) { fprintf(stderr,"USAGE: %s port\n", argv[0]); exit(1); }
// Set up the address struct for this process (the server)
memset((char *)&serverAddress, '\0', sizeof(serverAddress));
portNumber = atoi(argv[1]);
serverAddress.sin_family = AF_INET;
serverAddress.sin_port = htons(portNumber);
serverAddress.sin_addr.s_addr = INADDR_ANY;
// Set up the socket
listenSocketFD = socket(AF_INET, SOCK_STREAM, 0);
if (listenSocketFD < 0) error("ERROR opening socket");
// Enable the socket to begin listening
if (bind(listenSocketFD, (struct sockaddr *)&serverAddress, sizeof(serverAddress)) < 0)
error("ERROR on binding");
listen(listenSocketFD, 5);
while(1){
sizeOfClientInfo = sizeof(clientAddress);
establishedConnectionFD = accept(listenSocketFD, (struct sockaddr *)&clientAddress, &sizeOfClientInfo); // Accept
if (establishedConnectionFD < 0) error("ERROR on accept");
pid_t spawnPid = -5;
int childExitStatus = -5;
pid_t childPID;
do {
childPID = waitpid(-1, &childExitStatus, WNOHANG);
if (childPID>0){
numChildren--;
for (i=0; i<5; i++){
if (activeSpawn[i]==childPID){
activeSpawn[i]=-5;
break;
}
}
}
}while (childPID>0);
if (numChildren>4){
childPID = waitpid(-1, &childExitStatus, 0);
numChildren--;
for (i=0; i<5; i++){
if (activeSpawn[i]==childPID){
activeSpawn[i]=-5;
break;
}
}
}
spawnPid=fork();
switch (spawnPid) {
case -1: { perror("Hull Breach!\n"); exit(1); break; }
case 0: {
memset(clientID, '\0', 4);
memset(totalKey, '\0', sizeof(totalKey));
memset(totalMsg, '\0', sizeof(totalMsg));
memset(decodedMsg, '\0', sizeof(decodedMsg));
//Obtain the client identity:
charsRead = recv(establishedConnectionFD, clientID, strlen(clientID)-1, 0);
if (charsRead < 0) error("ERROR reading from socket");
//Refuse the connection if the client is not "enc"
if (strcmp(verifyID, clientID)) {
charsWritten = send(establishedConnectionFD, refuse, strlen(refuse), 0);
close(establishedConnectionFD);
exit(1);
}
//Send confirmation that server is ready to receive message length
charsWritten = send(establishedConnectionFD, ready, strlen(ready), 0);
if (charsRead < 0) error("ERROR writing to socket");
msgLength_beforeConvert=0;
msgLength=0;
charsRead = recv(establishedConnectionFD, &msgLength_beforeConvert, sizeof(uint32_t), 0);
if (charsRead < 0) error("ERROR reading from socket");
msgLength=ntohl(msgLength_beforeConvert);
//Send confirmation that server is ready to receive message:
charsWritten = send(establishedConnectionFD, ready, strlen(ready), 0);
if (charsWritten < 0) error("ERROR writing to socket");
charsRecCount=0;
//continue receiving the message from client until entire message is received.
while (charsRecCount<msgLength-1){
memset(buffer, '\0', 1000);
charsRead = recv(establishedConnectionFD, buffer, sizeof(buffer) - 1, 0);
if (charsRead < 0) error("ERROR reading from socket");
charsRecCount+=charsRead;
strcat(totalMsg, buffer);
}
//Send confirmation that server is ready to receive key:
charsWritten = send(establishedConnectionFD, ready, strlen(ready), 0); // Send success back
if (charsWritten < 0) error("ERROR writing to socket");
charsRecCount=0;
//continue receiving the message from client until entire message is received.
while (charsRecCount<msgLength-1){
memset(buffer, '\0', 1000);
charsRead = recv(establishedConnectionFD, buffer, sizeof(buffer) - 1, 0);
if (charsRead < 0) error("ERROR reading from socket");
charsRecCount+=charsRead;
strcat(totalKey, buffer);
}
for (i=0; i<msgLength-1; i++){
char difference;
//for each character in message received
//if character is a space, set to numerical value 26
if (totalMsg[i]==32) { totalMsg[i]=26; }
//else it is an alphbet characted A-Z. subtract 65 to have 'A'=0, 'B'=1... 'Y'=24, 'Z'=25
else totalMsg[i]-=65;
if (totalKey[i]==32) { totalKey[i]=26; }
else totalKey[i]-=65;
difference=(totalMsg[i]-totalKey[i]);
if (difference<0){difference+=27;}
//add the the msg character to the key character, and modulo 27. Then add 65 to get ASCII char
// if the numerical value is equal to 91 then it is a space. Set to correct ASCII number
decodedMsg[i]=((difference)%27)+65;
if (decodedMsg[i]==91) {decodedMsg[i]=32;}
}
charsWritten = send(establishedConnectionFD, decodedMsg, strlen(decodedMsg), 0); // Send encrypted message back
if (charsWritten < 0) error("ERROR writing to socket");
close(establishedConnectionFD);
exit(0);
}
default:{
pid_t childPID_actual = waitpid(spawnPid, &childExitStatus, WNOHANG);
if (childPID_actual==0){
numChildren++;
for (i=0; i<5; i++){
if (activeSpawn[i]==-5){
activeSpawn[i]=spawnPid;
break;
}
}
}
}
}
}
close(listenSocketFD); // Close the listening socket
return 0;
}