--- /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