/* -*-c-*-
*
- * $Id: keyset.c,v 1.3 2001/02/16 21:39:55 mdw Exp $
+ * $Id: keyset.c,v 1.9 2003/10/15 09:29:38 mdw Exp $
*
* Handling of symmetric keysets
*
/*----- Revision history --------------------------------------------------*
*
* $Log: keyset.c,v $
+ * Revision 1.9 2003/10/15 09:29:38 mdw
+ * Cosmetic fix to changelog comment.
+ *
+ * Revision 1.8 2003/07/13 11:19:49 mdw
+ * Incompatible protocol fix! Include message type code under MAC tag to
+ * prevent cut-and-paste from key-exchange messages to general packet
+ * transport.
+ *
+ * Revision 1.7 2003/05/17 11:00:47 mdw
+ * Don't make scary messages just because one key didn't work on a message:
+ * only be frightened if they all fail. Set initial keyset refcount
+ * correctly.
+ *
+ * Revision 1.6 2003/04/06 10:26:35 mdw
+ * Report peer name on decrypt errors.
+ *
+ * Revision 1.5 2001/06/19 22:07:43 mdw
+ * Change the encrypted packet format to be non-malleable.
+ *
+ * Revision 1.4 2001/06/16 14:06:40 mdw
+ * Quantify collision probabilities for the stated data volume bounds.
+ *
* Revision 1.3 2001/02/16 21:39:55 mdw
* Major overhaul. Separate functions for manipulating keysets from
* functions for manipulating keyset lists. Introduce a concept of
/*----- 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 %$2^{-19}$%.
+ */
+
#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 */
/*----- 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
*
* keyset is OK to use.
*/
-static int doencrypt(keyset *ks, buf *b, buf *bb)
+static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
{
ghash *h;
gcipher *c;
- size_t ivsz;
const octet *p = BCUR(b);
size_t sz = BLEFT(b);
- octet *qiv, *qseq, *qpk;
+ octet *qmac, *qseq, *qiv, *qpk;
uint32 oseq;
size_t osz, nsz;
+ octet t[4];
int rc = 0;
/* --- Allocate the required buffer space --- */
c = ks->cout;
- ivsz = c->ops->c->blksz;
- if (buf_ensure(bb, ivsz + 4 + sz))
+ if (buf_ensure(bb, MACSZ + SEQSZ + IVSZ + sz))
return (0); /* Caution! */
- qiv = BCUR(bb); qseq = qiv + ivsz; qpk = qseq + 4;
- BSTEP(bb, ivsz + 4 + sz);
+ qmac = BCUR(bb); qseq = qmac + MACSZ; qiv = qseq + SEQSZ; qpk = qiv + IVSZ;
+ BSTEP(bb, MACSZ + SEQSZ + IVSZ + sz);
+ STORE32(t, ty);
- /* --- MAC and encrypt the packet --- */
+ /* --- Encrypt the packet --- */
oseq = ks->oseq++; STORE32(qseq, oseq);
- h = ks->mout->ops->init(ks->mout);
- h->ops->hash(h, qseq, 4);
- h->ops->hash(h, p, sz);
- memcpy(qiv, h->ops->done(h, 0), ivsz);
- h->ops->destroy(h);
+ rand_get(RAND_GLOBAL, qiv, IVSZ);
+ c->ops->setiv(c, qiv);
+ c->ops->encrypt(c, p, qpk, sz);
IF_TRACING(T_KEYSET, {
trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
(unsigned long)oseq, ks->seq);
- trace_block(T_CRYPTO, "crypto: computed MAC", qiv, ivsz);
+ trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
})
- c->ops->setiv(c, qiv);
- c->ops->encrypt(c, p, qpk, sz);
+
+ /* --- Now compute the MAC --- */
+
+ h = ks->mout->ops->init(ks->mout);
+ h->ops->hash(h, t, sizeof(t));
+ h->ops->hash(h, qseq, SEQSZ + IVSZ + sz);
+ memcpy(qmac, h->ops->done(h, 0), MACSZ);
+ h->ops->destroy(h);
IF_TRACING(T_KEYSET, {
- trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
+ trace_block(T_CRYPTO, "crypto: computed MAC", qmac, MACSZ);
})
/* --- Deduct the packet size from the key's data life --- */
/* --- @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
* packet, and the packet's sequence number is stored in @*seq@.
*/
-static int dodecrypt(keyset *ks, buf *b, buf *bb, uint32 *seq)
+static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
{
- const octet *piv, *pseq, *ppk;
+ const octet *pmac, *piv, *pseq, *ppk;
size_t psz = BLEFT(b);
size_t sz;
octet *q = BCUR(bb);
size_t ivsz = c->ops->c->blksz;
octet *mac;
int eq;
+ octet t[4];
/* --- Break up the packet into its components --- */
T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
return (-1);
}
- sz = psz - ivsz - 4;
- piv = BCUR(b); pseq = piv + ivsz; ppk = pseq + 4;
+ sz = psz - IVSZ - SEQSZ - MACSZ;
+ pmac = BCUR(b); pseq = pmac + MACSZ; piv = pseq + SEQSZ; ppk = piv + IVSZ;
+ STORE32(t, ty);
- /* --- Attempt to decrypt the packet --- */
+ /* --- Verify the MAC on the packet --- */
- c->ops->setiv(c, piv);
- c->ops->decrypt(c, ppk, q, sz);
h = ks->min->ops->init(ks->min);
- h->ops->hash(h, pseq, 4);
- h->ops->hash(h, q, sz);
+ h->ops->hash(h, t, sizeof(t));
+ h->ops->hash(h, pseq, SEQSZ + IVSZ + sz);
mac = h->ops->done(h, 0);
- eq = !memcmp(mac, piv, ivsz);
+ eq = !memcmp(mac, pmac, MACSZ);
IF_TRACING(T_KEYSET, {
trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
- trace_block(T_CRYPTO, "crypto: computed MAC", mac, ivsz);
+ trace_block(T_CRYPTO, "crypto: computed MAC", mac, MACSZ);
})
h->ops->destroy(h);
if (!eq) {
IF_TRACING(T_KEYSET, {
- trace(T_KEYSET, "keyset: decryption failed");
- trace_block(T_CRYPTO, "crypto: expected MAC", piv, ivsz);
- trace_block(T_CRYPTO, "crypto: invalid packet", q, sz);
+ trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
+ trace_block(T_CRYPTO, "crypto: expected MAC", pmac, MACSZ);
})
return (-1);
}
+
+ /* --- Decrypt the packet --- */
+
+ c->ops->setiv(c, piv);
+ c->ops->decrypt(c, ppk, q, sz);
if (seq)
*seq = LOAD32(pseq);
IF_TRACING(T_KEYSET, {
*
* 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.
*
* calling @ks_encrypt@ directly.
*/
-keyset *ks_gen(const void *k, size_t x, size_t y, size_t z)
+keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
{
HASH_CTX h;
octet buf[HASHSZ];
keyset *ks = CREATE(keyset);
time_t now = time(0);
- const octet *p = k;
+ const octet *pp = k;
T( static unsigned seq = 0; )
T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
* This is done with macros, because it's quite tedious.
*/
-#define MINE HASH(&h, p, x)
-#define YOURS HASH(&h, p + x, y - x)
-#define OURS HASH(&h, p + y, z - y)
+#define MINE HASH(&h, pp, x)
+#define YOURS HASH(&h, pp + x, y - x)
+#define OURS HASH(&h, pp + y, z - y)
#define IN MINE; YOURS; OURS
#define OUT YOURS; MINE; OURS
#undef GETHASH
T( ks->seq = seq++; )
+ ks->ref = 1;
ks->t_exp = now + T_EXP;
ks->sz_exp = SZ_EXP;
ks->oseq = ks->iseq = 0;
ks->iwin = 0;
ks->next = 0;
+ ks->p = p;
ks->f = KSF_LISTEN;
BURN(buf);
return (ks);
/* --- @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
*
* used even if it's marked as not for data output.
*/
-int ks_encrypt(keyset *ks, buf *b, buf *bb)
+int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
{
time_t now = time(0);
buf_break(bb);
return (0);
}
- return (doencrypt(ks, b, bb));
+ 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
*
* marking that it's not for encryption.
*/
-int ks_decrypt(keyset *ks, buf *b, buf *bb)
+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, b, bb, &seq) ||
+ dodecrypt(ks, ty, b, bb, &seq) ||
dosequence(ks, seq))
return (-1);
return (0);
/* --- @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
*
* Use: Encrypts a packet.
*/
-int ksl_encrypt(keyset **ksroot, buf *b, buf *bb)
+int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
{
time_t now = time(0);
keyset *ks = *ksroot;
ks = ks->next;
}
- return (doencrypt(ks, b, bb));
+ 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
*
* Use: Decrypts a packet.
*/
-int ksl_decrypt(keyset **ksroot, buf *b, buf *bb)
+int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
{
time_t now = time(0);
keyset *ks;
for (ks = *ksroot; ks; ks = ks->next) {
if (!KEYOK(ks, now))
continue;
- if (!dodecrypt(ks, b, bb, &seq)) {
+ if (!dodecrypt(ks, ty, b, bb, &seq)) {
if (ks->f & KSF_LISTEN) {
T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
ks->seq); )
return (dosequence(ks, seq));
}
}
- T( trace(T_KEYSET, "keyset: no matching keys"); )
+ T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
return (-1);
}
~mdw / tripe / blobdiff