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exercise.c
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exercise.c
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#define MESSAGE_NUM 5
char* encryptString(char*,char*,size_t);
char* getKey(int);
void decryptAllMessage();
int checkPassword();
int getMessage(char*);
void printAllEncryptedMessages();
struct messages{
char* key;
char* encryptedString;
size_t len;
}message[MESSAGE_NUM];
int main()
{
srand(time(NULL));
char readString[255];
for(int i=0;i<MESSAGE_NUM;++i) {
memset(readString,0,255);
printf("Enter Message:\n");
int len = getMessage(readString);
char* key = getKey(len);
char* encryptedString = encryptString(readString,key,len);
message[i].key=key;
message[i].encryptedString = encryptedString;
message[i].len = len;
}
printf("Enter Password\n");
if(checkPassword())
{
decryptAllMessage();
}
else
printAllEncryptedMessages();
for(int i=0;i<MESSAGE_NUM;++i)
{
free(message[i].encryptedString);
free(message[i].key);
}
}
int getMessage(char* message)
{
return read(0,message,100);
}
int checkPassword()
{
char password[255];
size_t passwordLen = read(0,password,100);
return (passwordLen != 0) && (!memcmp(password,"password",8));
}
char* getKey(int len)
{
char* key = malloc(len);
for(int i=0;i<len;++i)
{
key[i]=rand();
}
return key;
}
char* encryptString(char* val,char* key, size_t len)
{
char* encryptedMessage = malloc(len);
for(int i=0;i<len;++i)
{
encryptedMessage[i] = val[i]^key[i];
}
return encryptedMessage;
}
void printAllEncryptedMessages()
{
for(int i=0;i<MESSAGE_NUM;++i)
{
printf("message %d:",i);
for(int j=0;j<message[i].len;++j)
{
printf("%c",message[i].encryptedString[j]);
}
printf("\n");
}
}
void decryptAllMessage()
{
for(int i=0;i<MESSAGE_NUM;++i)
{
printf("message %d:",i);
for(int j=0;j<message[i].len;++j)
{
printf("%c",message[i].encryptedString[j]^message[i].key[j]);
}
}
}