FreeBSD/Linux Kernel Cross Reference
sys/geom/bde/g_bde_crypt.c

     /*-
      * Copyright (c) 2002 Poul-Henning Kamp
      * Copyright (c) 2002 Networks Associates Technology, Inc.
      * All rights reserved.
      *
      * This software was developed for the FreeBSD Project by Poul-Henning Kamp
      * and NAI Labs, the Security Research Division of Network Associates, Inc.
      * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
      * DARPA CHATS research program.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD: releng/5.0/sys/geom/bde/g_bde_crypt.c 108891 2003-01-07 18:21:39Z phk $
     *
     * This source file contains the functions responsible for the crypto, keying
     * and mapping operations on the I/O requests.
     *
     */
    
    #include <sys/param.h>
    #include <sys/stdint.h>
    #include <sys/bio.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/queue.h>
    #include <sys/malloc.h>
    #include <sys/libkern.h>
    #include <sys/md5.h>
    
    #include <crypto/rijndael/rijndael.h>
    #include <crypto/sha2/sha2.h>
    
    #include <geom/geom.h>
    #include <geom/bde/g_bde.h>
    
    
    /*
     * Derive kkey from mkey + sector offset.
     *
     * Security objective: Derive a potentially very large number of distinct skeys
     * from the comparatively small key material in our mkey, in such a way that
     * if one, more or even many of the kkeys are compromised, this does not
     * significantly help an attack on other kkeys and in particular does not
     * weaken or compromised the mkey.
     *
     * First we MD5 hash the sectornumber with the salt from the lock sector.
     * The salt prevents the precalculation and statistical analysis of the MD5
     * output which would be possible if we only gave it the sectornumber.
     *
     * The MD5 hash is used to pick out 16 bytes from the masterkey, which
     * are then hashed with MD5 together with the sector number.
     *
     * The resulting MD5 hash is the kkey.
     */
    
    static void
    g_bde_kkey(struct g_bde_softc *sc, keyInstance *ki, int dir, off_t sector)
    {
            u_int t;
            MD5_CTX ct;
            u_char buf[16];
            u_char buf2[8];
    
            /* We have to be architecture neutral */
            g_enc_le8(buf2, sector);
    
            MD5Init(&ct);
            MD5Update(&ct, sc->key.salt, 8);
            MD5Update(&ct, buf2, sizeof buf2);
            MD5Update(&ct, sc->key.salt + 8, 8);
            MD5Final(buf, &ct);
    
            MD5Init(&ct);
            for (t = 0; t < 16; t++) {
                    MD5Update(&ct, &sc->key.mkey[buf[t]], 1);
                    if (t == 8)
                            MD5Update(&ct, buf2, sizeof buf2);
            }
            bzero(buf2, sizeof buf2);
            MD5Final(buf, &ct);
           bzero(&ct, sizeof ct);
           AES_makekey(ki, dir, G_BDE_KKEYBITS, buf);
           bzero(buf, sizeof buf);
   }
   
   /*
    * Encryption work for read operation.
    *
    * Security objective: Find the kkey, find the skey, decrypt the sector data.
    */
   
   void
   g_bde_crypt_read(struct g_bde_work *wp)
   {
           struct g_bde_softc *sc;
           u_char *d;
           u_int n;
           off_t o;
           u_char skey[G_BDE_SKEYLEN];
           keyInstance ki;
           cipherInstance ci;
           
   
           AES_init(&ci);
           sc = wp->softc;
           o = 0;
           for (n = 0; o < wp->length; n++, o += sc->sectorsize) {
                   d = (u_char *)wp->ksp->data + wp->ko + n * G_BDE_SKEYLEN;
                   g_bde_kkey(sc, &ki, DIR_DECRYPT, wp->offset + o);
                   AES_decrypt(&ci, &ki, d, skey, sizeof skey);
                   d = (u_char *)wp->data + o;
                   AES_makekey(&ki, DIR_DECRYPT, G_BDE_SKEYBITS, skey);
                   AES_decrypt(&ci, &ki, d, d, sc->sectorsize);
           }
           bzero(skey, sizeof skey);
           bzero(&ci, sizeof ci);
           bzero(&ki, sizeof ci);
   }
   
   /*
    * Encryption work for write operation.
    *
    * Security objective: Create random skey, encrypt sector data,
    * encrypt skey with the kkey.
    */
   
   void
   g_bde_crypt_write(struct g_bde_work *wp)
   {
           u_char *s, *d;
           struct g_bde_softc *sc;
           u_int n;
           off_t o;
           u_char skey[G_BDE_SKEYLEN];
           keyInstance ki;
           cipherInstance ci;
   
           sc = wp->softc;
           AES_init(&ci);
           o = 0;
           for (n = 0; o < wp->length; n++, o += sc->sectorsize) {
   
                   s = (u_char *)wp->data + o;
                   d = (u_char *)wp->sp->data + o;
                   arc4rand(&skey, sizeof skey, 0);
                   AES_makekey(&ki, DIR_ENCRYPT, G_BDE_SKEYBITS, skey);
                   AES_encrypt(&ci, &ki, s, d, sc->sectorsize);
   
                   d = (u_char *)wp->ksp->data + wp->ko + n * G_BDE_SKEYLEN;
                   g_bde_kkey(sc, &ki, DIR_ENCRYPT, wp->offset + o);
                   AES_encrypt(&ci, &ki, skey, d, sizeof skey);
                   bzero(skey, sizeof skey);
           }
           bzero(skey, sizeof skey);
           bzero(&ci, sizeof ci);
           bzero(&ki, sizeof ci);
   }
   
   /*
    * Encryption work for delete operation.
    *
    * Security objective: Write random data to the sectors.
    *
    * XXX: At a hit in performance we would trash the encrypted skey as well.
    * XXX: This would add frustration to the cleaning lady attack by making
    * XXX: deletes look like writes.
    */
   
   void
   g_bde_crypt_delete(struct g_bde_work *wp)
   {
           struct g_bde_softc *sc;
           u_char *d;
           off_t o;
           u_char skey[G_BDE_SKEYLEN];
           keyInstance ki;
           cipherInstance ci;
   
           sc = wp->softc;
           d = wp->sp->data;
           AES_init(&ci);
           /*
            * Do not unroll this loop!
            * Our zone may be significantly wider than the amount of random
            * bytes arc4rand likes to give in one reseeding, whereas our
            * sectorsize is far more likely to be in the same range.
            */
           for (o = 0; o < wp->length; o += sc->sectorsize) {
                   arc4rand(d, sc->sectorsize, 0);
                   arc4rand(&skey, sizeof skey, 0);
                   AES_makekey(&ki, DIR_ENCRYPT, G_BDE_SKEYBITS, skey);
                   AES_encrypt(&ci, &ki, d, d, sc->sectorsize);
                   d += sc->sectorsize;
           }
           /*
            * Having written a long random sequence to disk here, we want to
            * force a reseed, to avoid weakening the next time we use random
            * data for something important.
            */
           arc4rand(&o, sizeof o, 1);
   }
   
   /*
    * Calculate the total payload size of the encrypted device.
    *
    * Security objectives: none.
    *
    * This function needs to agree with g_bde_map_sector() about things.
    */
   
   uint64_t
   g_bde_max_sector(struct g_bde_key *kp)
   {
           uint64_t maxsect;
   
           maxsect = kp->media_width;
           maxsect /= kp->zone_width;
           maxsect *= kp->zone_cont;
           return (maxsect);
   }
   
   /*
    * Convert an unencrypted side offset to offsets on the encrypted side.
    *
    * Security objective:  Make it harder to identify what sectors contain what
    * on a "cold" disk image.
    *
    * We do this by adding the "keyoffset" from the lock to the physical sector
    * number modulus the available number of sectors.  Since all physical sectors
    * presumably look the same cold, this will do.
    *
    * As part of the mapping we have to skip the lock sectors which we know
    * the physical address off.  We also truncate the work packet, respecting
    * zone boundaries and lock sectors, so that we end up with a sequence of
    * sectors which are physically contiguous.
    *
    * Shuffling things further is an option, but the incremental frustration is
    * not currently deemed worth the run-time performance hit resulting from the
    * increased number of disk arm movements it would incur.
    *
    * This function offers nothing but a trivial diversion for an attacker able
    * to do "the cleaning lady attack" in its current static mapping form.
    */
   
   void
   g_bde_map_sector(struct g_bde_work *wp)
   {
   
           u_int   zone, zoff, u, len;
           uint64_t ko;
           struct g_bde_softc *sc;
           struct g_bde_key *kp;
   
           sc = wp->softc;
           kp = &sc->key;
   
           /* find which zone and the offset in it */
           zone = wp->offset / kp->zone_cont;
           zoff = wp->offset % kp->zone_cont;
   
           /* Calculate the offset of the key in the key sector */
           wp->ko = (zoff / kp->sectorsize) * G_BDE_SKEYLEN;
   
           /* restrict length to that zone */
           len = kp->zone_cont - zoff;
           if (len < wp->length)
                   wp->length = len;
   
           /* Find physical sector address */
           wp->so = zone * kp->zone_width + zoff;
           wp->so += kp->keyoffset;
           wp->so %= kp->media_width;
           wp->so += kp->sector0;
   
           /* The key sector is the last in this zone. */
           wp->kso = zone * kp->zone_width + kp->zone_cont;
           wp->kso += kp->keyoffset;
           wp->kso %= kp->media_width;
           wp->kso += kp->sector0; 
   
           /* Compensate for lock sectors */
           for (u = 0; u < G_BDE_MAXKEYS; u++) {
                   /* Find the start of this lock sector */
                   ko = kp->lsector[u] & ~(kp->sectorsize - 1);
   
                   if (wp->kso >= ko)
                           wp->kso += kp->sectorsize;
   
                   if (wp->so >= ko) {
                           /* lock sector before work packet */
                           wp->so += kp->sectorsize;
                   } else if ((wp->so + wp->length) > ko) {
                           /* lock sector in work packet, truncate */
                           wp->length = ko - wp->so;
                   }
           }
   
   #if 0
           printf("off %jd len %jd so %jd ko %jd kso %u\n",
               (intmax_t)wp->offset,
               (intmax_t)wp->length,
               (intmax_t)wp->so,
               (intmax_t)wp->kso,
               wp->ko);
   #endif
   }

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