cryptstring.c

并行算法实验用的源代码

/********************************************************************
 File:        cryptString.c
 Program use: Crypt
 Lab #:       3
********************************************************************/

/*******************************
Function:    cryptString 
Description: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Input:       string: string to be encrypted or decrypted
             key:    the used for decoding or encoding the string
             n:      n is a constant for all the key values
                     a strings for this project. Do not
                     change or alter the value of n.
Output:      After encryption/decryption has been performed,
             the new string is returned. 
********************************/
char* cryptString (char *string, 
               unsigned long int key,
               unsigned long int n
              ){
  unsigned long int msg, pmsg;
  unsigned      int char0, char1, char2;
  char              *newStr;
                int x, i; 

  msg = 0;
  newStr = (char*)malloc(sizeof(char) * strlen(string));

  for(x = 0; x < strlen(string); x = x + 2){    
    char0 = string[x];
    char1 = string[x+1];

    msg = (( char0       & ((1 << 1 * 8) - 1))
          |((char1 << 8) & ((1 << 2 * 8) - 1))
          );

    pmsg = msg;
    for(i = 1; i < key; i++){
      msg = (msg * pmsg) % n;
    }

    newStr[x]   = (  msg       & ( (1 << (1 * 8)) - 1) );
    newStr[x+1] = ( (msg >> 8) & ( (1 << (2 * 8)) - 1) );
  }
return(newStr);
}