Generate Random Password in C Post: 302203705

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Top Forums Programming Generate Random Password in C Post 302203705 by jim mcnamara on Monday 9th of June 2008 02:52:53 PM

06-09-2008

Registered User

Here is a simple algorithm:

Code:

#include <stdlib.h>
#include <time.h>

static int srand_called=0;

char *random_pw(char *dest)
{
    size_t len=0;
    char *p=dest;
    int three_in_a_row=0;
    int arr[128]={0x0};

	/* be sure to have called srand exactly one time */
	if(!srand_called)
	{
		srandom(time(NULL));
		srand_called=1;
	}
	*dest=0x0; /* int the destination string*/
	for(len=6 + rand()%3; len; len--, p++) /* gen characters */
	{
		char *q=dest;
		*p=(rand()%2)? rand()%26 + 97: rand()%10 + 48;
		p[1]=0x0;
		arr[*p]++;                         /* check values */
		if(arr[*p]==3)
		{
			for(q=dest; q[2]>0 && !three_in_a_row; q++)	
				if(*q==q[1] && q[1]==q[2])
			   		three_in_a_row=1;
		}
		if(three_in_a_row || arr[*p]> 3 )
			return random_pw(dest);        /* values do not pass try again */
	}
    return dest;
}

Last edited by jim mcnamara; 06-11-2008 at 05:59 PM.. Reason: change srand to srandom

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LEARN ABOUT REDHAT

strcpy

STRCPY(3)						     Linux Programmer's Manual							 STRCPY(3)

NAME

       strcpy, strncpy - copy a string

SYNOPSIS

       #include <string.h>

       char *strcpy(char *dest, const char *src);

       char *strncpy(char *dest, const char *src, size_t n);

DESCRIPTION

       The  strcpy() function copies the string pointed to by src (including the terminating `' character) to the array pointed to by dest.  The
       strings may not overlap, and the destination string dest must be large enough to receive the copy.

       The strncpy() function is similar, except that not more than n bytes of src are copied. Thus, if there is no null byte among  the  first  n
       bytes of src, the result will not be null-terminated.

       In the case where the length of src is less than that of n, the remainder of dest will be padded with nulls.

RETURN VALUE

       The strcpy() and strncpy() functions return a pointer to the destination string dest.

BUGS

       If  the	destination  string  of  a  strcpy() is not large enough (that is, if the programmer was stupid/lazy, and failed to check the size
       before copying) then anything might happen.  Overflowing fixed length strings is a favourite cracker technique.

CONFORMING TO

       SVID 3, POSIX, BSD 4.3, ISO 9899

SEE ALSO

       bcopy(3), memccpy(3), memcpy(3), memmove(3)

GNU
								    1993-04-11								 STRCPY(3)

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