+++ /dev/null
-/* -*-c-*-
- *
- * $Id$
- *
- * Handling of symmetric keysets
- *
- * (c) 2001 Straylight/Edgeware
- */
-
-/*----- Licensing notice --------------------------------------------------*
- *
- * This file is part of Trivial IP Encryption (TrIPE).
- *
- * TrIPE is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * TrIPE is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with TrIPE; if not, write to the Free Software Foundation,
- * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- */
-
-/*----- Header files ------------------------------------------------------*/
-
-#include "tripe.h"
-
-/*----- Tunable parameters ------------------------------------------------*/
-
-/* --- Note on size limits --- *
- *
- * For a 64-bit block cipher (e.g., Blowfish), the probability of a collision
- * occurring after 32 MB is less than %$2^{-21}$%, and the probability of a
- * collision occurring after 64 MB is less than %$2^{-19}$%. These could be
- * adjusted dependent on the encryption scheme, but it's too much pain.
- */
-
-#define T_EXP MIN(60) /* Expiry time for a key */
-#define T_REGEN MIN(45) /* Regeneration time for a key */
-#define SZ_EXP MEG(64) /* Expiry data size for a key */
-#define SZ_REGEN MEG(32) /* Data size threshold for regen */
-
-/*----- Handy macros ------------------------------------------------------*/
-
-#define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
-
-#define SEQSZ 4 /* Size of sequence number packet */
-
-/*----- Low-level packet encryption and decryption ------------------------*/
-
-/* --- Encrypted data format --- *
- *
- * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
- * compute
- *
- * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
- *
- * as the CBC-ciphertext of %$p_i$%, and then
- *
- * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
- *
- * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
- * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
- * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
- * [Bellare and Namprempre].
- *
- * This also ensures that, assuming the key is good, we have a secure channel
- * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
- * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
- * then-encrypt scheme and still have a secure channel. However, I like the
- * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
- * the Horton Principle [Wagner and Schneier].
- */
-
-/* --- @doencrypt@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to keyset to use
- * @unsigned ty@ = type of message this is
- * @buf *b@ = pointer to an input buffer
- * @buf *bb@ = pointer to an output buffer
- *
- * Returns: Zero if OK, nonzero if a new key is required.
- *
- * Use: Encrypts a message with the given key. We assume that the
- * keyset is OK to use.
- */
-
-static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
-{
- ghash *h;
- gcipher *c = ks->cout;
- const octet *p = BCUR(b);
- size_t sz = BLEFT(b);
- octet *qmac, *qseq, *qiv, *qpk;
- uint32 oseq;
- size_t ivsz = GC_CLASS(c)->blksz;
- size_t tagsz = ks->tagsz;
- size_t osz, nsz;
- octet t[4];
- int rc = 0;
-
- /* --- Allocate the required buffer space --- */
-
- if (buf_ensure(bb, tagsz + SEQSZ + ivsz + sz))
- return (0); /* Caution! */
- qmac = BCUR(bb); qseq = qmac + tagsz; qiv = qseq + SEQSZ; qpk = qiv + ivsz;
- BSTEP(bb, tagsz + SEQSZ + ivsz + sz);
- STORE32(t, ty);
-
- oseq = ks->oseq++; STORE32(qseq, oseq);
- IF_TRACING(T_KEYSET, {
- trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
- (unsigned long)oseq, ks->seq);
- trace_block(T_CRYPTO, "crypto: plaintext packet", p, sz);
- })
-
- /* --- Encrypt the packet --- */
-
- if (ivsz) {
- rand_get(RAND_GLOBAL, qiv, ivsz);
- GC_SETIV(c, qiv);
- IF_TRACING(T_KEYSET, {
- trace_block(T_CRYPTO, "crypto: initialization vector", qiv, ivsz);
- })
- }
- GC_ENCRYPT(c, p, qpk, sz);
- IF_TRACING(T_KEYSET, {
- trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
- })
-
- /* --- Now compute the MAC --- */
-
- if (tagsz) {
- h = GM_INIT(ks->mout);
- GH_HASH(h, t, sizeof(t));
- GH_HASH(h, qseq, SEQSZ + ivsz + sz);
- memcpy(qmac, GH_DONE(h, 0), tagsz);
- GH_DESTROY(h);
- IF_TRACING(T_KEYSET, {
- trace_block(T_CRYPTO, "crypto: computed MAC", qmac, tagsz);
- })
- }
-
- /* --- Deduct the packet size from the key's data life --- */
-
- osz = ks->sz_exp;
- if (osz > sz)
- nsz = osz - sz;
- else
- nsz = 0;
- if (osz >= SZ_REGEN && nsz < SZ_REGEN) {
- T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
- "forcing exchange", ks->seq); )
- rc = -1;
- }
- ks->sz_exp = nsz;
- return (rc);
-}
-
-/* --- @dodecrypt@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to keyset to use
- * @unsigned ty@ = expected type code
- * @buf *b@ = pointer to an input buffer
- * @buf *bb@ = pointer to an output buffer
- * @uint32 *seq@ = where to store the sequence number
- *
- * Returns: Zero if OK, nonzero if it failed.
- *
- * Use: Attempts to decrypt a message with the given key. No other
- * checking (e.g., sequence number checks) is performed. We
- * assume that the keyset is OK to use, and that there is
- * sufficient output buffer space reserved. If the decryption
- * is successful, the buffer pointer is moved past the decrypted
- * packet, and the packet's sequence number is stored in @*seq@.
- */
-
-static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
-{
- const octet *pmac, *piv, *pseq, *ppk;
- size_t psz = BLEFT(b);
- size_t sz;
- octet *q = BCUR(bb);
- ghash *h;
- gcipher *c = ks->cin;
- size_t ivsz = GC_CLASS(c)->blksz;
- size_t tagsz = ks->tagsz;
- octet *mac;
- int eq;
- octet t[4];
-
- /* --- Break up the packet into its components --- */
-
- if (psz < ivsz + SEQSZ + tagsz) {
- T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
- return (-1);
- }
- sz = psz - ivsz - SEQSZ - tagsz;
- pmac = BCUR(b); pseq = pmac + tagsz; piv = pseq + SEQSZ; ppk = piv + ivsz;
- STORE32(t, ty);
-
- IF_TRACING(T_KEYSET, {
- trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
- trace_block(T_CRYPTO, "crypto: ciphertext packet", ppk, sz);
- })
-
- /* --- Verify the MAC on the packet --- */
-
- if (tagsz) {
- h = GM_INIT(ks->min);
- GH_HASH(h, t, sizeof(t));
- GH_HASH(h, pseq, SEQSZ + ivsz + sz);
- mac = GH_DONE(h, 0);
- eq = !memcmp(mac, pmac, tagsz);
- IF_TRACING(T_KEYSET, {
- trace_block(T_CRYPTO, "crypto: computed MAC", mac, tagsz);
- })
- GH_DESTROY(h);
- if (!eq) {
- IF_TRACING(T_KEYSET, {
- trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
- trace_block(T_CRYPTO, "crypto: expected MAC", pmac, tagsz);
- })
- return (-1);
- }
- }
-
- /* --- Decrypt the packet --- */
-
- if (ivsz) {
- GC_SETIV(c, piv);
- IF_TRACING(T_KEYSET, {
- trace_block(T_CRYPTO, "crypto: initialization vector", piv, ivsz);
- })
- }
- GC_DECRYPT(c, ppk, q, sz);
- if (seq)
- *seq = LOAD32(pseq);
- IF_TRACING(T_KEYSET, {
- trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
- (unsigned long)LOAD32(pseq));
- trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
- })
- BSTEP(bb, sz);
- return (0);
-}
-
-/*----- Operations on a single keyset -------------------------------------*/
-
-/* --- @ks_drop@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to a keyset
- *
- * Returns: ---
- *
- * Use: Decrements a keyset's reference counter. If the counter hits
- * zero, the keyset is freed.
- */
-
-void ks_drop(keyset *ks)
-{
- if (--ks->ref)
- return;
- GC_DESTROY(ks->cin);
- GC_DESTROY(ks->cout);
- GM_DESTROY(ks->min);
- GM_DESTROY(ks->mout);
- DESTROY(ks);
-}
-
-/* --- @ks_gen@ --- *
- *
- * Arguments: @const void *k@ = pointer to key material
- * @size_t x, y, z@ = offsets into key material (see below)
- * @peer *p@ = pointer to peer information
- *
- * Returns: A pointer to the new keyset.
- *
- * Use: Derives a new keyset from the given key material. The
- * offsets @x@, @y@ and @z@ separate the key material into three
- * parts. Between the @k@ and @k + x@ is `my' contribution to
- * the key material; between @k + x@ and @k + y@ is `your'
- * contribution; and between @k + y@ and @k + z@ is a shared
- * value we made together. These are used to construct two
- * pairs of symmetric keys. Each pair consists of an encryption
- * key and a message authentication key. One pair is used for
- * outgoing messages, the other for incoming messages.
- *
- * The new key is marked so that it won't be selected for output
- * by @ksl_encrypt@. You can still encrypt data with it by
- * calling @ks_encrypt@ directly.
- */
-
-keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
-{
- ghash *h;
- const octet *hh;
- keyset *ks = CREATE(keyset);
- time_t now = time(0);
- const octet *pp = k;
- T( static unsigned seq = 0; )
-
- T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
-
- /* --- Construct the various keys --- *
- *
- * This is done with macros, because it's quite tedious.
- */
-
-#define MINE GH_HASH(h, pp, x)
-#define YOURS GH_HASH(h, pp + x, y - x)
-#define OURS GH_HASH(h, pp + y, z - y)
-
-#define HASH_in MINE; YOURS; OURS
-#define HASH_out YOURS; MINE; OURS
-#define INIT_c(k) GC_INIT(algs.c, (k), algs.cksz)
-#define INIT_m(k) GM_KEY(algs.m, (k), algs.mksz)
-#define STR_c "encryption"
-#define STR_m "integrity"
-#define STR_in "incoming"
-#define STR_out "outgoing"
-
-#define SETKEY(a, dir) do { \
- h = GH_INIT(algs.h); \
- HASH_STRING(h, "tripe-" STR_##a); \
- HASH_##dir; \
- hh = GH_DONE(h, 0); \
- IF_TRACING(T_KEYSET, { \
- trace_block(T_CRYPTO, "crypto: " STR_##dir " key " STR_##a, \
- hh, algs.a##ksz); \
- }) \
- ks->a##dir = INIT_##a(hh); \
- GH_DESTROY(h); \
-} while (0)
-
- SETKEY(c, in); SETKEY(c, out);
- SETKEY(m, in); SETKEY(m, out);
-
-#undef MINE
-#undef YOURS
-#undef OURS
-#undef STR_c
-#undef STR_m
-#undef STR_in
-#undef STR_out
-#undef INIT_c
-#undef INIT_m
-#undef HASH_in
-#undef HASH_out
-#undef SETKEY
-
- T( ks->seq = seq++; )
- ks->ref = 1;
- ks->t_exp = now + T_EXP;
- ks->sz_exp = SZ_EXP;
- ks->oseq = 0;
- seq_reset(&ks->iseq);
- ks->next = 0;
- ks->p = p;
- ks->f = KSF_LISTEN;
- ks->tagsz = algs.tagsz;
- return (ks);
-}
-
-/* --- @ks_tregen@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to a keyset
- *
- * Returns: The time at which moves ought to be made to replace this key.
- */
-
-time_t ks_tregen(keyset *ks) { return (ks->t_exp - T_EXP + T_REGEN); }
-
-/* --- @ks_activate@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to a keyset
- *
- * Returns: ---
- *
- * Use: Activates a keyset, so that it can be used for encrypting
- * outgoing messages.
- */
-
-void ks_activate(keyset *ks)
-{
- if (ks->f & KSF_LISTEN) {
- T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
- ks->f &= ~KSF_LISTEN;
- }
-}
-
-/* --- @ks_encrypt@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to a keyset
- * @unsigned ty@ = message type
- * @buf *b@ = pointer to input buffer
- * @buf *bb@ = pointer to output buffer
- *
- * Returns: Zero if OK, nonzero if the key needs replacing. If the
- * encryption failed, the output buffer is broken and zero is
- * returned.
- *
- * Use: Encrypts a block of data using the key. Note that the `key
- * ought to be replaced' notification is only ever given once
- * for each key. Also note that this call forces a keyset to be
- * used even if it's marked as not for data output.
- */
-
-int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
-{
- time_t now = time(0);
-
- if (!KEYOK(ks, now)) {
- buf_break(bb);
- return (0);
- }
- return (doencrypt(ks, ty, b, bb));
-}
-
-/* --- @ks_decrypt@ --- *
- *
- * Arguments: @keyset *ks@ = pointer to a keyset
- * @unsigned ty@ = expected type code
- * @buf *b@ = pointer to an input buffer
- * @buf *bb@ = pointer to an output buffer
- *
- * Returns: Zero on success, or nonzero if there was some problem.
- *
- * Use: Attempts to decrypt a message using a given key. Note that
- * requesting decryption with a key directly won't clear a
- * marking that it's not for encryption.
- */
-
-int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
-{
- time_t now = time(0);
- uint32 seq;
-
- if (!KEYOK(ks, now) ||
- buf_ensure(bb, BLEN(b)) ||
- dodecrypt(ks, ty, b, bb, &seq) ||
- seq_check(&ks->iseq, seq, "SYMM"))
- return (-1);
- return (0);
-}
-
-/*----- Keyset list handling ----------------------------------------------*/
-
-/* --- @ksl_free@ --- *
- *
- * Arguments: @keyset **ksroot@ = pointer to keyset list head
- *
- * Returns: ---
- *
- * Use: Frees (releases references to) all of the keys in a keyset.
- */
-
-void ksl_free(keyset **ksroot)
-{
- keyset *ks, *ksn;
- for (ks = *ksroot; ks; ks = ksn) {
- ksn = ks->next;
- ks->f &= ~KSF_LINK;
- ks_drop(ks);
- }
-}
-
-/* --- @ksl_link@ --- *
- *
- * Arguments: @keyset **ksroot@ = pointer to keyset list head
- * @keyset *ks@ = pointer to a keyset
- *
- * Returns: ---
- *
- * Use: Links a keyset into a list. A keyset can only be on one list
- * at a time. Bad things happen otherwise.
- */
-
-void ksl_link(keyset **ksroot, keyset *ks)
-{
- assert(!(ks->f & KSF_LINK));
- ks->next = *ksroot;
- *ksroot = ks;
- ks->f |= KSF_LINK;
- ks->ref++;
-}
-
-/* --- @ksl_prune@ --- *
- *
- * Arguments: @keyset **ksroot@ = pointer to keyset list head
- *
- * Returns: ---
- *
- * Use: Prunes the keyset list by removing keys which mustn't be used
- * any more.
- */
-
-void ksl_prune(keyset **ksroot)
-{
- time_t now = time(0);
-
- while (*ksroot) {
- keyset *ks = *ksroot;
-
- if (ks->t_exp <= now) {
- T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
- ks->seq); )
- goto kill;
- } else if (ks->sz_exp == 0) {
- T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
- ks->seq); )
- goto kill;
- } else {
- ksroot = &ks->next;
- continue;
- }
-
- kill:
- *ksroot = ks->next;
- ks->f &= ~KSF_LINK;
- ks_drop(ks);
- }
-}
-
-/* --- @ksl_encrypt@ --- *
- *
- * Arguments: @keyset **ksroot@ = pointer to keyset list head
- * @unsigned ty@ = message type
- * @buf *b@ = pointer to input buffer
- * @buf *bb@ = pointer to output buffer
- *
- * Returns: Nonzero if a new key is needed.
- *
- * Use: Encrypts a packet.
- */
-
-int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
-{
- time_t now = time(0);
- keyset *ks = *ksroot;
-
- for (;;) {
- if (!ks) {
- T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
- buf_break(bb);
- return (-1);
- }
- if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
- break;
- ks = ks->next;
- }
-
- return (doencrypt(ks, ty, b, bb));
-}
-
-/* --- @ksl_decrypt@ --- *
- *
- * Arguments: @keyset **ksroot@ = pointer to keyset list head
- * @unsigned ty@ = expected type code
- * @buf *b@ = pointer to input buffer
- * @buf *bb@ = pointer to output buffer
- *
- * Returns: Nonzero if the packet couldn't be decrypted.
- *
- * Use: Decrypts a packet.
- */
-
-int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
-{
- time_t now = time(0);
- keyset *ks;
- uint32 seq;
-
- if (buf_ensure(bb, BLEN(b)))
- return (-1);
-
- for (ks = *ksroot; ks; ks = ks->next) {
- if (!KEYOK(ks, now))
- continue;
- if (!dodecrypt(ks, ty, b, bb, &seq)) {
- if (ks->f & KSF_LISTEN) {
- T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
- ks->seq); )
- ks->f &= ~KSF_LISTEN;
- }
- return (seq_check(&ks->iseq, seq, "SYMM"));
- }
- }
- T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
- return (-1);
-}
-
-/*----- That's all, folks -------------------------------------------------*/
~mdw / tripe / blobdiff