#include <u.h>#include <libc.h>#include <auth.h> enum{	CHALLEN	= 2*AUTHLEN + 2*NAMELEN,	RESPLEN	= 2*AUTHLEN + NAMELEN + DESKEYLEN,	SULEN	= AUTHLEN + NAMELEN + DESKEYLEN,	MAXLEN	= 2*AUTHLEN + 2*NAMELEN + DESKEYLEN,}; static void	gethostname(char*, char*);static int	dofcrypt(int, char*, char*, int); /* * c -> h -> a	KC{KH{RXschal, hchal}, host, RXcchal, cchal}, client * a -> h -> c	KC{KH{RXstick, hchal, client, KC}, RXctick, cchal} * c -> h	KH{RXstick, hchal, client, KC} */char *auth(int tohost, char *dialstring){	char *user, buf[MAXLEN], hchal[AUTHLEN], chal[AUTHLEN], host[NAMELEN];	ulong t;	int i, j, crypt; 	user = getuser();	crypt = open("#c/crypt", ORDWR);	if(crypt < 0)		return "can't open crypt device"; 	gethostname(host, dialstring);	/*	 * build the challenge to send to the server	 */	if(read(tohost, hchal, AUTHLEN) != AUTHLEN){		close(crypt);		return "can't read server challenge";	}	i = 0;	memmove(&buf[i], hchal, AUTHLEN);	i += AUTHLEN;	strncpy(&buf[i], host, NAMELEN);	i += NAMELEN;	/*	 * just fake a random challenge	 */	buf[i++] = RXcchal;	t = getpid();	for(j = 1; j < AUTHLEN/2; j++)		buf[i++] = t >> (8*j);	t = time(0);	for( ; j < AUTHLEN; j++)		buf[i++] = t >> (8*j);	memmove(chal, &buf[i-AUTHLEN], AUTHLEN);	if(dofcrypt(crypt, "E", buf, i) < 0){		close(crypt);		return "can't encrypt data";	}	strncpy(&buf[i], user, NAMELEN);	i += NAMELEN; 	/*	 * send it and get the string to change the user name	 */	if(write(tohost, buf, i) != i){		close(crypt);		return "can't write challenge";	}	if(read(tohost, buf, RESPLEN) != RESPLEN){		close(crypt);		return "authentication failed";	} 	/*	 * decrypt it and check the challenge string	 */	if(dofcrypt(crypt, "D", buf, RESPLEN) < 0){		close(crypt);		return "can't decrypt data";	}	close(crypt);	i = AUTHLEN + NAMELEN + DESKEYLEN;	chal[0] = RXctick;	if(memcmp(chal, &buf[i], AUTHLEN) != 0)		return "challenge mismatch";	if(write(tohost, buf, SULEN) != SULEN)		return "can't write to server";	if(read(tohost, buf, 2) != 2 || buf[0] != 'O' || buf[1] != 'K')		return "server rejected connection";	return 0;} /* * extract a host name from the dial string * form [net!]host[!service] * assumes net! over !service * any leading slashes in host are ignored * and then if host has a '.', it ends the name * * does not understand ip addresses like 135.102.117.34 */static voidgethostname(char *name, char *dialstring){	char *p, *q;	int n; 	/*	 * strip optional net! and then !service	 */	n = NAMELEN - 1;	p = utfrune(dialstring, L'!');	if(p){		p++;		if(q = utfrune(p, L'!'))			n = q - p;	}else		p = dialstring; 	/*	 * strip leading slashes	 */	while((q = utfrune(p, L'/')) && q < p + n){		q++;		n -= q - p;		p = q;	}	if(n > NAMELEN - 1)		n = NAMELEN - 1;	strncpy(name, p, n);	name[n] = '\0';	/*	 * wipe out \..*	 */	if(p = utfrune(name, '.'))		*p = '\0';} /* * encrypt/decrypt data using a crypt device */static intdofcrypt(int fd, char *how, char *s, int n){		if(write(fd, how, 1) < 1)		return -1;	seek(fd, 0, 0);	if(write(fd, s, n) < n)		return -1;	seek(fd, 0, 0);	if(read(fd, s, n) < n)		return -1;	return n;}