/*- * 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. * * $FreeBSD$ * * This source file contains the functions responsible for the crypto, keying * and mapping operations on the I/O requests. * */ #include #include #include #include #include #include #include #include #include #include #include #include #include /* * 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; sc = wp->softc; d = wp->sp->data; /* * 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); 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 should be enough. * * 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_key *kp, uint64_t isector, uint64_t *osector, uint64_t *ksector, u_int *koffset) { u_int zone, zoff, zidx, u; uint64_t os; /* find which zone and the offset and index in it */ zone = isector / kp->zone_cont; zoff = isector % kp->zone_cont; zidx = zoff / kp->sectorsize; /* Find physical sector address */ os = zone * kp->zone_width + zoff; os += kp->keyoffset; os %= kp->media_width - (G_BDE_MAXKEYS * kp->sectorsize); os += kp->sector0; /* Compensate for lock sectors */ for (u = 0; u < G_BDE_MAXKEYS; u++) if (os >= kp->lsector[u]) os += kp->sectorsize; *osector = os; /* The key sector is the last in this zone. */ os = (1 + zone) * kp->zone_width - kp->sectorsize; os += kp->keyoffset; os %= kp->media_width - (G_BDE_MAXKEYS * kp->sectorsize); os += kp->sector0; for (u = 0; u < G_BDE_MAXKEYS; u++) if (os >= kp->lsector[u]) os += kp->sectorsize; *ksector = os; *koffset = zidx * G_BDE_SKEYLEN; #if 0 printf("off %jd %jd %jd %u\n", (intmax_t)isector, (intmax_t)*osector, (intmax_t)*ksector, *koffset); #endif }