auth_md5.c

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/* ========================================================================
 * Copyright 1988-2007 University of Washington
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * 
 * ========================================================================
 */

/*
 * Program:	CRAM-MD5 authenticator
 *
 * Author:	Mark Crispin
 *		Networks and Distributed Computing
 *		Computing & Communications
 *		University of Washington
 *		Administration Building, AG-44
 *		Seattle, WA  98195
 *		Internet: [e-mail]
 *
 * Date:	21 October 1998
 * Last Edited:	30 January 2007
 */

/* MD5 context */

#define MD5BLKLEN 64		/* MD5 block length */
#define MD5DIGLEN 16		/* MD5 digest length */

typedef struct {
  unsigned long chigh;		/* high 32bits of byte count */
  unsigned long clow;		/* low 32bits of byte count */
  unsigned long state[4];	/* state (ABCD) */
  unsigned char buf[MD5BLKLEN];	/* input buffer */
  unsigned char *ptr;		/* buffer position */
} MD5CONTEXT;


/* Prototypes */

long auth_md5_valid (void);
long auth_md5_client (authchallenge_t challenger,authrespond_t responder,
		      char *service,NETMBX *mb,void *stream,
		      unsigned long *trial,char *user);
char *auth_md5_server (authresponse_t responder,int argc,char *argv[]);
char *auth_md5_pwd (char *user);
char *apop_login (char *chal,char *user,char *md5,int argc,char *argv[]);
char *hmac_md5 (char *text,unsigned long tl,char *key,unsigned long kl);
void md5_init (MD5CONTEXT *ctx);
void md5_update (MD5CONTEXT *ctx,unsigned char *data,unsigned long len);
void md5_final (unsigned char *digest,MD5CONTEXT *ctx);
static void md5_transform (unsigned long *state,unsigned char *block);
static void md5_encode (unsigned char *dst,unsigned long *src,int len);
static void md5_decode (unsigned long *dst,unsigned char *src,int len);


/* Authenticator linkage */

AUTHENTICATOR auth_md5 = {
  AU_SECURE,			/* secure authenticator */
  "CRAM-MD5",			/* authenticator name */
  auth_md5_valid,		/* check if valid */
  auth_md5_client,		/* client method */
  auth_md5_server,		/* server method */
  NIL				/* next authenticator */
};

/* Check if CRAM-MD5 valid on this system
 * Returns: T, always
 */

long auth_md5_valid (void)
{
  struct stat sbuf;
				/* server forbids MD5 if no MD5 enable file */
  if (stat (MD5ENABLE,&sbuf)) auth_md5.server = NIL;
  return T;			/* MD5 is otherwise valid */
}


/* Client authenticator
 * Accepts: challenger function
 *	    responder function
 *	    SASL service name
 *	    parsed network mailbox structure
 *	    stream argument for functions
 *	    pointer to current trial count
 *	    returned user name
 * Returns: T if success, NIL otherwise, number of trials incremented if retry
 */

long auth_md5_client (authchallenge_t challenger,authrespond_t responder,
		      char *service,NETMBX *mb,void *stream,
		      unsigned long *trial,char *user)
{
  char pwd[MAILTMPLEN];
  void *challenge;
  unsigned long clen;
  long ret = NIL;
				/* get challenge */
  if (challenge = (*challenger) (stream,&clen)) {
    pwd[0] = NIL;		/* prompt user */
    mm_login (mb,user,pwd,*trial);
    if (!pwd[0]) {		/* user requested abort */
      fs_give ((void **) &challenge);
      (*responder) (stream,NIL,0);
      *trial = 0;		/* cancel subsequent attempts */
      ret = LONGT;		/* will get a BAD response back */
    }
    else {			/* got password, build response */
      sprintf (pwd,"%.65s %.33s",user,hmac_md5 (challenge,clen,
						pwd,strlen (pwd)));
      fs_give ((void **) &challenge);
				/* send credentials, allow retry if OK */
      if ((*responder) (stream,pwd,strlen (pwd))) {
	if (challenge = (*challenger) (stream,&clen))
	  fs_give ((void **) &challenge);
	else {
	  ++*trial;		/* can try again if necessary */
	  ret = LONGT;		/* check the authentication */
	}
      }
    }
  }
  memset (pwd,0,MAILTMPLEN);	/* erase password in case not overwritten */
  if (!ret) *trial = 65535;	/* don't retry if bad protocol */
  return ret;
}

/* Server authenticator
 * Accepts: responder function
 *	    argument count
 *	    argument vector
 * Returns: authenticated user name or NIL
 *
 * This is much hairier than it needs to be due to the necessary of zapping
 * the password data.
 */

static int md5try = MAXLOGINTRIALS;

char *auth_md5_server (authresponse_t responder,int argc,char *argv[])
{
  char *ret = NIL;
  char *p,*u,*user,*authuser,*hash,chal[MAILTMPLEN];
  unsigned long cl,pl;
				/* generate challenge */
  sprintf (chal,"<%lu.%lu@%s>",(unsigned long) getpid (),
	   (unsigned long) time (0),mylocalhost ());
				/* send challenge, get user and hash */
  if (user = (*responder) (chal,cl = strlen (chal),NIL)) {
				/* got user, locate hash */
    if (hash = strrchr (user,' ')) {
      *hash++ = '\0';		/* tie off user */
				/* see if authentication user */
      if (authuser = strchr (user,'*')) *authuser++ = '\0';
				/* get password */
      if (p = auth_md5_pwd ((authuser && *authuser) ? authuser : user)) {
	pl = strlen (p);
	u = (md5try && !strcmp (hash,hmac_md5 (chal,cl,p,pl))) ? user : NIL;
	memset (p,0,pl);	/* erase sensitive information */
	fs_give ((void **) &p);	/* flush erased password */
				/* now log in for real */
	if (u && authserver_login (u,authuser,argc,argv)) ret = myusername ();
	else if (md5try) --md5try;
      }
    }
    fs_give ((void **) &user);
  }
  if (!ret) sleep (3);		/* slow down possible cracker */
  return ret;
}

/* Return MD5 password for user
 * Accepts: user name
 * Returns: plaintext password if success, else NIL
 *
 * This is much hairier than it needs to be due to the necessary of zapping
 * the password data.  That's why we don't use stdio here.
 */

char *auth_md5_pwd (char *user)
{
  struct stat sbuf;
  int fd = open (MD5ENABLE,O_RDONLY,NIL);
  unsigned char *s,*t,*buf,*lusr,*lret;
  char *r;
  char *ret = NIL;
  if (fd >= 0) {		/* found the file? */
    fstat (fd,&sbuf);		/* yes, slurp it into memory */
    read (fd,buf = (char *) fs_get (sbuf.st_size + 1),sbuf.st_size);
				/* see if any uppercase characters in user */
    for (s = user; *s && ((*s < 'A') || (*s > 'Z')); s++);
				/* yes, make lowercase copy */
    lusr = *s ? lcase (cpystr (user)) : NIL;
    for (s = strtok_r ((char *) buf,"\015\012",&r),lret = NIL; s;
	 s = ret ? NIL : strtok_r (NIL,"\015\012",&r))
				/* must be valid entry line */
      if (*s && (*s != '#') && (t = strchr (s,'\t')) && t[1]) {
	*t++ = '\0';		/* found tab, tie off user, point to pwd */
	if (!strcmp (s,user)) ret = cpystr (t);
	else if (lusr && !lret) if (!strcmp (s,lusr)) lret = t;
      }
				/* accept case-independent name */
    if (!ret && lret) ret = cpystr (lret);
				/* don't need lowercase copy any more */
    if (lusr) fs_give ((void **) &lusr);
				/* erase sensitive information from buffer */
    memset (buf,0,sbuf.st_size + 1);
    fs_give ((void **) &buf);	/* flush the buffer */
    close (fd);			/* don't need file any longer */
  }
  return ret;			/* return password */
}

/* APOP server login
 * Accepts: challenge
 *	    desired user name
 *	    purported MD5
 *	    argument count
 *	    argument vector
 * Returns: authenticated user name or NIL
 */

char *apop_login (char *chal,char *user,char *md5,int argc,char *argv[])
{
  int i,j;
  char *ret = NIL;
  char *s,*authuser,tmp[MAILTMPLEN];
  unsigned char digest[MD5DIGLEN];
  MD5CONTEXT ctx;
  char *hex = "0123456789abcdef";
				/* see if authentication user */
  if (authuser = strchr (user,'*')) *authuser++ = '\0';
				/* get password */
  if (s = auth_md5_pwd ((authuser && *authuser) ? authuser : user)) {
    md5_init (&ctx);		/* initialize MD5 context */
				/* build string to get MD5 digest */
    sprintf (tmp,"%.128s%.128s",chal,s);
    memset (s,0,strlen (s));	/* erase sensitive information */
    fs_give ((void **) &s);	/* flush erased password */
    md5_update (&ctx,(unsigned char *) tmp,strlen (tmp));
    memset (tmp,0,MAILTMPLEN);	/* erase sensitive information */
    md5_final (digest,&ctx);