/*   Login code for S/KEY Authentication.  S/KEY is a trademark
 *   of Bellcore.
 *
 *   Mink is the former name of the S/KEY authentication system.
 *   Many reference for mink  may still be found in this program.   */
 
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include "skey.h"

#define	KEYFILE	"/etc/skeykeys"

char *skipspace();
int skeylookup __ARGS((struct skey *mp,char *name));


/* Issue a skey challenge for user 'name'. If successful,
 * fill in the caller's skey structure and return 0. If unsuccessful
 * (e.g., if name is unknown) return -1.
 *
 * The file read/write pointer is left at the start of the
 * record.
 */
int
skeychallenge(mp,name)
struct skey *mp;
char *name;
{
	int rval;

	rval = skeylookup(mp,name);
	switch(rval){
	case -1:	/* File error */
		return -1;
	case 0:		/* Lookup succeeded, issue challenge */
		printf("s/key %d %s\n",mp->n - 1,mp->seed);
		return 0;
	case 1:		/* User not found */
		fclose(mp->keyfile);
		return -1;
	}
	return -1;	/* Can't happen */
}	

/* Find an entry in the One-time Password database.
 * Return codes:
 * -1: error in opening database
 *  0: entry found, file R/W pointer positioned at beginning of record
 *  1: entry not found, file R/W pointer positioned at EOF
 */
int
skeylookup(mp,name)
struct skey *mp;
char *name;
{
	int found;
	int len;
	long recstart;
	char *cp;
	struct stat statbuf;

	/* See if the KEYFILE exists, and create it if not */
	if(stat(KEYFILE,&statbuf) == -1 && errno == ENOENT){
		mp->keyfile = fopen(KEYFILE,"w+");
	} else {
		/* Otherwise open normally for update */
		mp->keyfile = fopen(KEYFILE,"r+");
	}
	if(mp->keyfile == NULL)
		return -1;

	/* Look up user name in database */
	len = strlen(name);
	if( len > 8 ) len = 8;		/*  Added 8/2/91  -  nmh */
	found = 0;
	while(!feof(mp->keyfile)){
		recstart = ftell(mp->keyfile);
		if(fgets(mp->buf,sizeof(mp->buf),mp->keyfile) != mp->buf){
			break;
		}
		rip(mp->buf);
		if(mp->buf[0] == '#')
			continue;	/* Comment */
		if((mp->logname = strtok(mp->buf," \t")) == NULL)
			continue;
		if((cp = strtok(NULL," \t")) == NULL)
			continue;
		mp->n = atoi(cp);
		if((mp->seed = strtok(NULL," \t")) == NULL)
			continue;
		if((mp->val = strtok(NULL," \t")) == NULL)
			continue;
		if(strlen(mp->logname) == len
		 && strncmp(mp->logname,name,len) == 0){
			found = 1;
			break;
		}
	}
	if(found){
		fseek(mp->keyfile,recstart,0);
		return 0;
	} else
		return 1;
}
/* Verify response to a s/key challenge.
 *
 * Return codes:
 * -1: Error of some sort; database unchanged
 *  0:  Verify successful, database updated
 *  1:  Verify failed, database unchanged
 *
 * The database file is always closed by this call.
 */
int
skeyverify(mp,response)
struct skey *mp;
char *response;
{
	char key[8];
	char fkey[8];
	char filekey[8];

	if(response == NULL){
		fclose(mp->keyfile);
		return -1;
	}
	rip(response);

	/* Convert response to binary */
	if(etob(key,response) != 1 && atob8(key,response) != 0){
		/* Neither english words or ascii hex */
		fclose(mp->keyfile);
		return -1;
	}

	/* Compute fkey = f(key) */
	memcpy(fkey,key,sizeof(key));
	f(fkey);

	/* And convert file value to hex for comparison */
	atob8(filekey,mp->val);

	/* Do actual comparison */
	if(memcmp(filekey,fkey,8) != 0){
		/* Wrong response */
		fclose(mp->keyfile);
		return 1;
	}

	/* Update key in database by overwriting entire record. Note
	 * that we must write exactly the same number of bytes as in
	 * the original record (note fixed width field for N)
	 */
	btoa8(mp->val,key);
	mp->n--;
	fprintf(mp->keyfile,"%s %04d %-16s %s",mp->logname,mp->n,mp->seed,
	 mp->val);
	fclose(mp->keyfile);
	return 0;
}


/* Convert 8-byte hex-ascii string to binary array
 * Returns 0 on success, -1 on error
 */
atob8(out,in)
register char *out,*in;
{
	register int i;
	register int val;

	if(in == NULL || out == NULL)
		return -1;

	for(i=0;i<8;i++){
		if((in = skipspace(in)) == NULL)
			return -1;
		if((val = htoi(*in++)) == -1)
			return -1;
		*out = val << 4;

		if((in = skipspace(in)) == NULL)
			return -1;
		if((val = htoi(*in++)) == -1)
			return -1;
		*out++ |= val;
	}
	return 0;
}

char *
skipspace(cp)
register char *cp;
{
	while(*cp == ' ' || *cp == '\t')
		cp++;

	if(*cp == '\0')
		return NULL;
	else
		return cp;
}

/* Convert 8-byte binary array to hex-ascii string */
int
btoa8(out,in)
register char *out,*in;
{
	register int i;

	if(in == NULL || out == NULL)
		return -1;

	for(i=0;i<8;i++){
		sprintf(out,"%02x",*in++ & 0xff);
		out += 2;
	}
	return 0;
}


/* Convert hex digit to binary integer */
int
htoi(c)
register char c;
{
	if('0' <= c && c <= '9')
		return c - '0';
	if('a' <= c && c <= 'f')
		return 10 + c - 'a';
	if('A' <= c && c <= 'F')
		return 10 + c - 'A';
	return -1;
}