X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/tripe/blobdiff_plain/e6b06b6b61b4b877937d4a56ba704d3f18154dc2..786989941b7b4504f0234c4a318f929802e981ad:/keyset.c diff --git a/keyset.c b/keyset.c deleted file mode 100644 index bb2397fc..00000000 --- a/keyset.c +++ /dev/null @@ -1,598 +0,0 @@ -/* -*-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 -------------------------------------------------*/