\ Copyright (c) 2016 Thomas Pornin \ \ Permission is hereby granted, free of charge, to any person obtaining \ a copy of this software and associated documentation files (the \ "Software"), to deal in the Software without restriction, including \ without limitation the rights to use, copy, modify, merge, publish, \ distribute, sublicense, and/or sell copies of the Software, and to \ permit persons to whom the Software is furnished to do so, subject to \ the following conditions: \ \ The above copyright notice and this permission notice shall be \ included in all copies or substantial portions of the Software. \ \ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, \ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF \ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND \ NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS \ BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN \ ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN \ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE \ SOFTWARE. \ ---------------------------------------------------------------------- \ Handshake processing code, for the server. \ The common T0 code (ssl_hs_common.t0) shall be read first. preamble { /* * This macro evaluates to a pointer to the server context, under that * specific name. It must be noted that since the engine context is the * first field of the br_ssl_server_context structure ('eng'), then * pointers values of both types are interchangeable, modulo an * appropriate cast. This also means that "addresses" computed as offsets * within the structure work for both kinds of context. */ #define CTX ((br_ssl_server_context *)ENG) /* * Decrypt the pre-master secret (RSA key exchange). */ static void do_rsa_decrypt(br_ssl_server_context *ctx, int prf_id, unsigned char *epms, size_t len) { uint32_t x; unsigned char rpms[48]; /* * Decrypt the PMS. */ x = (*ctx->policy_vtable)->do_keyx(ctx->policy_vtable, epms, &len); /* * Set the first two bytes to the maximum supported client * protocol version. These bytes are used for version rollback * detection; forceing the two bytes will make the master secret * wrong if the bytes are not correct. This process is * recommended by RFC 5246 (section 7.4.7.1). */ br_enc16be(epms, ctx->client_max_version); /* * Make a random PMS and copy it above the decrypted value if the * decryption failed. Note that we use a constant-time conditional * copy. */ br_hmac_drbg_generate(&ctx->eng.rng, rpms, sizeof rpms); br_ccopy(x ^ 1, epms, rpms, sizeof rpms); /* * Compute master secret. */ br_ssl_engine_compute_master(&ctx->eng, prf_id, epms, 48); /* * Clear the pre-master secret from RAM: it is normally a buffer * in the context, hence potentially long-lived. */ memset(epms, 0, len); } /* * Common part for ECDH and ECDHE. */ static void ecdh_common(br_ssl_server_context *ctx, int prf_id, unsigned char *xcoor, size_t xcoor_len, uint32_t ctl) { unsigned char rpms[80]; if (xcoor_len > sizeof rpms) { xcoor_len = sizeof rpms; ctl = 0; } /* * Make a random PMS and copy it above the decrypted value if the * decryption failed. Note that we use a constant-time conditional * copy. */ br_hmac_drbg_generate(&ctx->eng.rng, rpms, xcoor_len); br_ccopy(ctl ^ 1, xcoor, rpms, xcoor_len); /* * Compute master secret. */ br_ssl_engine_compute_master(&ctx->eng, prf_id, xcoor, xcoor_len); /* * Clear the pre-master secret from RAM: it is normally a buffer * in the context, hence potentially long-lived. */ memset(xcoor, 0, xcoor_len); } /* * Do the ECDH key exchange (not ECDHE). */ static void do_ecdh(br_ssl_server_context *ctx, int prf_id, unsigned char *cpoint, size_t cpoint_len) { uint32_t x; /* * Finalise the key exchange. */ x = (*ctx->policy_vtable)->do_keyx(ctx->policy_vtable, cpoint, &cpoint_len); ecdh_common(ctx, prf_id, cpoint, cpoint_len, x); } /* * Do the full static ECDH key exchange. When this function is called, * it has already been verified that the cipher suite uses ECDH (not ECDHE), * and the client's public key (from its certificate) has type EC and is * apt for key exchange. */ static void do_static_ecdh(br_ssl_server_context *ctx, int prf_id) { unsigned char cpoint[133]; size_t cpoint_len; const br_x509_class **xc; const br_x509_pkey *pk; xc = ctx->eng.x509ctx; pk = (*xc)->get_pkey(xc, NULL); cpoint_len = pk->key.ec.qlen; if (cpoint_len > sizeof cpoint) { /* * If the point is larger than our buffer then we need to * restrict it. Length 2 is not a valid point length, so * the ECDH will fail. */ cpoint_len = 2; } memcpy(cpoint, pk->key.ec.q, cpoint_len); do_ecdh(ctx, prf_id, cpoint, cpoint_len); } static size_t hash_data(br_ssl_server_context *ctx, void *dst, int hash_id, const void *src, size_t len) { const br_hash_class *hf; br_hash_compat_context hc; if (hash_id == 0) { unsigned char tmp[36]; hf = br_multihash_getimpl(&ctx->eng.mhash, br_md5_ID); if (hf == NULL) { return 0; } hf->init(&hc.vtable); hf->update(&hc.vtable, src, len); hf->out(&hc.vtable, tmp); hf = br_multihash_getimpl(&ctx->eng.mhash, br_sha1_ID); if (hf == NULL) { return 0; } hf->init(&hc.vtable); hf->update(&hc.vtable, src, len); hf->out(&hc.vtable, tmp + 16); memcpy(dst, tmp, 36); return 36; } else { hf = br_multihash_getimpl(&ctx->eng.mhash, hash_id); if (hf == NULL) { return 0; } hf->init(&hc.vtable); hf->update(&hc.vtable, src, len); hf->out(&hc.vtable, dst); return (hf->desc >> BR_HASHDESC_OUT_OFF) & BR_HASHDESC_OUT_MASK; } } /* * Do the ECDHE key exchange (part 1: generation of transient key, and * computing of the point to send to the client). Returned value is the * signature length (in bytes), or -x on error (with x being an error * code). The encoded point is written in the ecdhe_point[] context buffer * (length in ecdhe_point_len). */ static int do_ecdhe_part1(br_ssl_server_context *ctx, int curve) { unsigned algo_id; unsigned mask; const unsigned char *order; size_t olen, glen; size_t hv_len, sig_len; if (!((ctx->eng.iec->supported_curves >> curve) & 1)) { return -BR_ERR_INVALID_ALGORITHM; } ctx->eng.ecdhe_curve = curve; /* * Generate our private key. We need a non-zero random value * which is lower than the curve order, in a "large enough" * range. We force the top bit to 0 and bottom bit to 1, which * does the trick. Note that contrary to what happens in ECDSA, * this is not a problem if we do not cover the full range of * possible values. */ order = ctx->eng.iec->order(curve, &olen); mask = 0xFF; while (mask >= order[0]) { mask >>= 1; } br_hmac_drbg_generate(&ctx->eng.rng, ctx->ecdhe_key, olen); ctx->ecdhe_key[0] &= mask; ctx->ecdhe_key[olen - 1] |= 0x01; ctx->ecdhe_key_len = olen; /* * Compute our ECDH point. */ glen = ctx->eng.iec->mulgen(ctx->eng.ecdhe_point, ctx->ecdhe_key, olen, curve); ctx->eng.ecdhe_point_len = glen; /* * Assemble the message to be signed, and possibly hash it. */ memcpy(ctx->eng.pad, ctx->eng.client_random, 32); memcpy(ctx->eng.pad + 32, ctx->eng.server_random, 32); ctx->eng.pad[64 + 0] = 0x03; ctx->eng.pad[64 + 1] = 0x00; ctx->eng.pad[64 + 2] = curve; ctx->eng.pad[64 + 3] = ctx->eng.ecdhe_point_len; memcpy(ctx->eng.pad + 64 + 4, ctx->eng.ecdhe_point, ctx->eng.ecdhe_point_len); hv_len = 64 + 4 + ctx->eng.ecdhe_point_len; algo_id = ctx->sign_hash_id; if (algo_id >= (unsigned)0xFF00) { hv_len = hash_data(ctx, ctx->eng.pad, algo_id & 0xFF, ctx->eng.pad, hv_len); if (hv_len == 0) { return -BR_ERR_INVALID_ALGORITHM; } } sig_len = (*ctx->policy_vtable)->do_sign(ctx->policy_vtable, algo_id, ctx->eng.pad, hv_len, sizeof ctx->eng.pad); return sig_len ? (int)sig_len : -BR_ERR_INVALID_ALGORITHM; } /* * Do the ECDHE key exchange (part 2: computation of the shared secret * from the point sent by the client). */ static void do_ecdhe_part2(br_ssl_server_context *ctx, int prf_id, unsigned char *cpoint, size_t cpoint_len) { int curve; uint32_t ctl; size_t xoff, xlen; curve = ctx->eng.ecdhe_curve; /* * Finalise the key exchange. */ ctl = ctx->eng.iec->mul(cpoint, cpoint_len, ctx->ecdhe_key, ctx->ecdhe_key_len, curve); xoff = ctx->eng.iec->xoff(curve, &xlen); ecdh_common(ctx, prf_id, cpoint + xoff, xlen, ctl); /* * Clear the ECDHE private key. Forward Secrecy is achieved insofar * as that key does not get stolen, so we'd better destroy it * as soon as it ceases to be useful. */ memset(ctx->ecdhe_key, 0, ctx->ecdhe_key_len); } /* * Offset for hash value within the pad (when obtaining all hash values, * in preparation for verification of the CertificateVerify message). * Order is MD5, SHA-1, SHA-224, SHA-256, SHA-384, SHA-512; last value * is used to get the total length. */ static const unsigned char HASH_PAD_OFF[] = { 0, 16, 36, 64, 96, 144, 208 }; /* * OID for hash functions in RSA signatures. */ static const unsigned char HASH_OID_SHA1[] = { 0x05, 0x2B, 0x0E, 0x03, 0x02, 0x1A }; static const unsigned char HASH_OID_SHA224[] = { 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04 }; static const unsigned char HASH_OID_SHA256[] = { 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01 }; static const unsigned char HASH_OID_SHA384[] = { 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02 }; static const unsigned char HASH_OID_SHA512[] = { 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03 }; static const unsigned char *HASH_OID[] = { HASH_OID_SHA1, HASH_OID_SHA224, HASH_OID_SHA256, HASH_OID_SHA384, HASH_OID_SHA512 }; /* * Verify the signature in CertificateVerify. Returned value is 0 on * success, or a non-zero error code. Lack of implementation of the * designated signature algorithm is reported as a "bad signature" * error (because it means that the peer did not honour our advertised * set of supported signature algorithms). */ static int verify_CV_sig(br_ssl_server_context *ctx, size_t sig_len) { const br_x509_class **xc; const br_x509_pkey *pk; int id; id = ctx->hash_CV_id; xc = ctx->eng.x509ctx; pk = (*xc)->get_pkey(xc, NULL); if (pk->key_type == BR_KEYTYPE_RSA) { unsigned char tmp[64]; const unsigned char *hash_oid; if (id == 0) { hash_oid = NULL; } else { hash_oid = HASH_OID[id - 2]; } if (ctx->eng.irsavrfy == 0) { return BR_ERR_BAD_SIGNATURE; } if (!ctx->eng.irsavrfy(ctx->eng.pad, sig_len, hash_oid, ctx->hash_CV_len, &pk->key.rsa, tmp) || memcmp(tmp, ctx->hash_CV, ctx->hash_CV_len) != 0) { return BR_ERR_BAD_SIGNATURE; } } else { if (ctx->eng.iecdsa == 0) { return BR_ERR_BAD_SIGNATURE; } if (!ctx->eng.iecdsa(ctx->eng.iec, ctx->hash_CV, ctx->hash_CV_len, &pk->key.ec, ctx->eng.pad, sig_len)) { return BR_ERR_BAD_SIGNATURE; } } return 0; } } \ ======================================================================= : addr-ctx: next-word { field } "addr-" field + 0 1 define-word 0 8191 "offsetof(br_ssl_server_context, " field + ")" + make-CX postpone literal postpone ; ; addr-ctx: client_max_version addr-ctx: client_suites addr-ctx: client_suites_num addr-ctx: hashes addr-ctx: curves addr-ctx: sign_hash_id \ Get address and length of the client_suites[] buffer. Length is expressed \ in bytes. : addr-len-client_suites ( -- addr len ) addr-client_suites CX 0 1023 { BR_MAX_CIPHER_SUITES * sizeof(br_suite_translated) } ; \ Read the client SNI extension. : read-client-sni ( lim -- lim ) \ Open extension value. read16 open-elt \ Open ServerNameList. read16 open-elt \ Find if there is a name of type 0 (host_name) with a length \ that fits in our dedicated buffer. begin dup while read8 if read-ignore-16 else read16 dup 255 <= if dup addr-server_name + 0 swap set8 addr-server_name swap read-blob else skip-blob then then repeat \ Close ServerNameList. close-elt \ Close extension value. close-elt ; \ Set the new maximum fragment length. BEWARE: this shall be called only \ after reading the ClientHello and before writing the ServerHello. cc: set-max-frag-len ( len -- ) { size_t max_frag_len = T0_POP(); br_ssl_engine_new_max_frag_len(ENG, max_frag_len); /* * We must adjust our own output limit. Since we call this only * after receiving a ClientHello and before beginning to send * the ServerHello, the next output record should be empty at * that point, so we can use max_frag_len as a limit. */ if (ENG->hlen_out > max_frag_len) { ENG->hlen_out = max_frag_len; } } \ Read the client Max Frag Length extension. : read-client-frag ( lim -- lim ) \ Extension value must have length exactly 1 byte. read16 1 <> if ERR_BAD_FRAGLEN fail then read8 \ The byte value must be 1, 2, 3 or 4. dup dup 0= swap 5 >= or if ERR_BAD_FRAGLEN fail then \ If our own maximum fragment length is greater, then we reduce \ our length. 8 + dup addr-log_max_frag_len get8 < if dup 1 swap << set-max-frag-len dup addr-log_max_frag_len set8 addr-peer_log_max_frag_len set8 else drop then ; \ Read the Secure Renegotiation extension from the client. : read-client-reneg ( lim -- lim ) \ Get value length. read16 \ The "reneg" value is one of: \ 0 on first handshake, client support is unknown \ 1 client does not support secure renegotiation \ 2 client supports secure renegotiation addr-reneg get8 case 0 of \ First handshake, value length shall be 1. 1 = ifnot ERR_BAD_SECRENEG fail then read8 if ERR_BAD_SECRENEG fail then 2 addr-reneg set8 endof 2 of \ Renegotiation, value shall consist of 13 bytes \ (header + copy of the saved client "Finished"). 13 = ifnot ERR_BAD_SECRENEG fail then read8 12 = ifnot ERR_BAD_SECRENEG fail then addr-pad 12 read-blob addr-saved_finished addr-pad 12 memcmp ifnot ERR_BAD_SECRENEG fail then endof \ If "reneg" is 1 then the client is not supposed to support \ the extension, and it sends it nonetheless, which means \ foul play. ERR_BAD_SECRENEG fail endcase ; \ Read the Signature Algorithms extension. : read-signatures ( lim -- lim ) \ Open extension value. read16 open-elt read-list-sign-algos addr-hashes set32 \ Close extension value. close-elt ; \ Read the Supported Curves extension. : read-supported-curves ( lim -- lim ) \ Open extension value. read16 open-elt \ Open list of curve identifiers. read16 open-elt \ Get all supported curves. 0 addr-curves set32 begin dup while read16 dup 32 < if 1 swap << addr-curves get32 or addr-curves set32 else drop then repeat close-elt close-elt ; \ Read the ALPN extension from client. : read-ALPN-from-client ( lim -- lim ) \ If we do not have configured names, then we just ignore the \ extension. addr-protocol_names_num get16 ifnot read-ignore-16 ret then \ Open extension value. read16 open-elt \ Open list of protocol names. read16 open-elt \ Get all names and test for their support. We keep the one with \ the lowest index (because we apply server's preferences, as \ recommended by RFC 7301, section 3.2. We set the 'found' variable \ to -2 and use an unsigned comparison, making -2 a huge value. -2 { found } begin dup while read8 dup { len } addr-pad swap read-blob len test-protocol-name dup found u< if >found else drop then repeat \ End of extension. close-elt close-elt \ Write back found name index (or not). If no match was found, \ then we write -1 (0xFFFF) in the index value, not 0, so that \ the caller knows that we tried to match, and failed. found 1+ addr-selected_protocol set16 ; \ Call policy handler to get cipher suite, hash function identifier and \ certificate chain. Returned value is 0 (false) on failure. cc: call-policy-handler ( -- bool ) { int x; br_ssl_server_choices choices; x = (*CTX->policy_vtable)->choose( CTX->policy_vtable, CTX, &choices); ENG->session.cipher_suite = choices.cipher_suite; CTX->sign_hash_id = choices.algo_id; ENG->chain = choices.chain; ENG->chain_len = choices.chain_len; T0_PUSHi(-(x != 0)); } \ Check for a remembered session. cc: check-resume ( -- bool ) { if (ENG->session.session_id_len == 32 && CTX->cache_vtable != NULL && (*CTX->cache_vtable)->load( CTX->cache_vtable, CTX, &ENG->session)) { T0_PUSHi(-1); } else { T0_PUSH(0); } } \ Save the current session. cc: save-session ( -- ) { if (CTX->cache_vtable != NULL) { (*CTX->cache_vtable)->save( CTX->cache_vtable, CTX, &ENG->session); } } \ Read and drop ClientHello. This is used when a client-triggered \ renegotiation attempt is rejected. : skip-ClientHello ( -- ) read-handshake-header-core 1 = ifnot ERR_UNEXPECTED fail then dup skip-blob drop ; \ Read ClientHello. If the session is resumed, then -1 is returned. : read-ClientHello ( -- resume ) \ Get header, and check message type. read-handshake-header 1 = ifnot ERR_UNEXPECTED fail then \ Get maximum protocol version from client. read16 dup { client-version-max } addr-client_max_version set16 \ Client random. addr-client_random 32 read-blob \ Client session ID. read8 dup 32 > if ERR_OVERSIZED_ID fail then dup addr-session_id_len set8 addr-session_id swap read-blob \ Lookup session for resumption. We should do that here because \ we need to verify that the remembered cipher suite is still \ matched by this ClientHello. check-resume { resume } \ Cipher suites. We read all cipher suites from client, each time \ matching against our own list. We accumulate suites in the \ client_suites[] context buffer: we keep suites that are \ supported by both the client and the server (so the list size \ cannot exceed that of the server list), and we keep them in \ either client or server preference order (depending on the \ relevant flag). \ \ We also need to identify the pseudo cipher suite for secure \ renegotiation here. read16 open-elt 0 { reneg-scsv } 0 { resume-suite } addr-len-client_suites dup2 bzero over + { css-off css-max } begin dup while read16 dup { suite } \ Check that when resuming a session, the requested \ suite is still valid. resume if dup addr-cipher_suite get16 = if -1 >resume-suite then then \ Special handling for TLS_EMPTY_RENEGOTIATION_INFO_SCSV. \ This fake cipher suite may occur only in the first \ handshake. dup 0x00FF = if addr-reneg get8 if ERR_BAD_SECRENEG fail then -1 >reneg-scsv then \ Special handling for TLS_FALLBACK_SCSV. If the client \ maximum version is less than our own maximum version, \ then this is an undue downgrade. We mark it by setting \ the client max version to 0x10000. dup 0x5600 = if client-version-max addr-version_min get16 >= client-version-max addr-version_max get16 < and if -1 >client-version-max then then \ Test whether the suite is supported by the server. scan-suite dup 0< if \ We do not support this cipher suite. Note \ that this also covers the case of pseudo \ cipher suites. drop else \ If we use server order, then we place the \ suite at the computed offset; otherwise, we \ append it to the list at the current place. 0 flag? if 2 << addr-client_suites + suite swap set16 else drop \ We need to test for list length because \ the client list may have duplicates, \ that we do not filter. Duplicates are \ invalid so this is not a problem if we \ reject such clients. css-off css-max >= if ERR_BAD_HANDSHAKE fail then suite css-off set16 css-off 4 + >css-off then then repeat drop \ Compression methods. We need method 0 (no compression). 0 { ok-compression } read8 open-elt begin dup while read8 ifnot -1 >ok-compression then repeat close-elt \ Set default values for parameters that may be affected by \ extensions: \ -- server name is empty \ -- client is reputed to know RSA and ECDSA, both with SHA-1 \ -- the default elliptic curve is P-256 (secp256r1, id = 23) 0 addr-server_name set8 0x0404 addr-hashes set32 0x800000 addr-curves set32 \ Process extensions, if any. dup if read16 open-elt begin dup while read16 case \ Server Name Indication. 0x0000 of read-client-sni endof \ Max Frag Length. 0x0001 of read-client-frag endof \ Secure Renegotiation. 0xFF01 of read-client-reneg endof \ Signature Algorithms. 0x000D of read-signatures endof \ Supported Curves. 0x000A of read-supported-curves endof \ Supported Point Formats. \ We only support "uncompressed", that all \ implementations are supposed to support, \ so we can simply ignore that extension. \ 0x000B of \ read-ignore-16 \ endof \ ALPN 0x0010 of read-ALPN-from-client endof \ Other extensions are ignored. drop read-ignore-16 0 endcase repeat close-elt then \ Close message. close-elt \ Cancel session resumption if the cipher suite was not found. resume resume-suite and >resume \ Now check the received data. Since the client is expecting an \ answer, we can send an appropriate fatal alert on any error. \ Compute protocol version as the minimum of our maximum version, \ and the maximum version sent by the client. If that is less than \ 0x0300 (SSL-3.0), then fail. Otherwise, we may at least send an \ alert with that version. We still reject versions lower than our \ configured minimum. \ As a special case, in case of undue downgrade, we send a specific \ alert (see RFC 7507). Note that this case may happen only if \ we would otherwise accept the client's version. client-version-max 0< if addr-client_max_version get16 addr-version_out set16 86 fail-alert then addr-version_max get16 dup client-version-max > if drop client-version-max then dup 0x0300 < if ERR_BAD_VERSION fail then client-version-max addr-version_min get16 < if 70 fail-alert then \ If resuming the session, then enforce the previously negotiated \ version (if still possible). resume if addr-version get16 client-version-max <= if drop addr-version get16 else 0 >resume then then dup addr-version set16 dup addr-version_in set16 dup addr-version_out set16 0x0303 >= { can-tls12 } \ If the client sent TLS_EMPTY_RENEGOTIATION_INFO_SCSV, then \ we should mark the client as "supporting secure renegotiation". reneg-scsv if 2 addr-reneg set8 then \ If, at that point, the 'reneg' value is still 0, then the client \ did not send the extension or the SCSV, so we have to assume \ that secure renegotiation is not supported by that client. addr-reneg get8 ifnot 1 addr-reneg set8 then \ Check compression. ok-compression ifnot 40 fail-alert then \ Filter hash function support by what the server also supports. \ If no common hash function remains with RSA and/or ECDSA, then \ the corresponding ECDHE suites are not possible. supported-hash-functions drop 257 * 0xFFFF0000 or addr-hashes get32 and dup addr-hashes set32 \ In 'can-ecdhe', bit 12 is set if ECDHE_RSA is possible, bit 13 is \ set if ECDHE_ECDSA is possible. dup 0xFF and 0<> neg swap 8 >> 0<> 2 and or 12 << { can-ecdhe } \ Filter supported curves. If there is no common curve between \ client and us, then ECDHE suites cannot be used. Note that we \ may still allow ECDH, depending on the EC key handler. addr-curves get32 supported-curves and dup addr-curves set32 ifnot 0 >can-ecdhe then \ If resuming a session, then the next steps are not necessary; \ we won't invoke the policy handler. resume if -1 ret then \ We are not resuming, so a new session ID should be generated. \ We don't check that the new ID is distinct from the one sent \ by the client because probability of such an event is 2^(-256), \ i.e. much (much) lower than that of an undetected transmission \ error or hardware miscomputation, and with similar consequences \ (handshake simply fails). addr-session_id 32 mkrand 32 addr-session_id_len set8 \ Translate common cipher suites, then squeeze out holes: there \ may be holes because of the way we fill the list when the \ server preference order is enforced, and also in case some \ suites are filtered out. In particular: \ -- ECDHE suites are removed if there is no common hash function \ (for the relevant signature algorithm) or no common curve. \ -- TLS-1.2-only suites are removed if the negotiated version is \ TLS-1.1 or lower. addr-client_suites dup >css-off begin dup css-max < while dup get16 dup cipher-suite-to-elements dup 12 >> dup 1 = swap 2 = or if dup can-ecdhe and ifnot 2drop 0 dup then then can-tls12 ifnot \ Suites compatible with TLS-1.0 and TLS-1.1 are \ exactly the ones that use HMAC/SHA-1. dup 0xF0 and 0x20 <> if 2drop 0 dup then then dup if css-off 2+ set16 css-off set16 css-off 4 + >css-off else 2drop then 4 + repeat drop css-off addr-client_suites - 2 >> dup ifnot \ No common cipher suite: handshake failure. 40 fail-alert then addr-client_suites_num set8 \ Check ALPN. addr-selected_protocol get16 0xFFFF = if 3 flag? if 120 fail-alert then 0 addr-selected_protocol set16 then \ Call policy handler to obtain the cipher suite and other \ parameters. call-policy-handler ifnot 40 fail-alert then \ We are not resuming a session. 0 ; \ Write ServerHello. : write-ServerHello ( initial -- ) { initial } \ Compute ServerHello length. 2 write8 70 \ Compute length of Secure Renegotiation extension. addr-reneg get8 2 = if initial if 5 else 29 then else 0 then { ext-reneg-len } \ Compute length of Max Fragment Length extension. addr-peer_log_max_frag_len get8 if 5 else 0 then { ext-max-frag-len } \ Compute length of ALPN extension. This also copy the \ selected protocol name into the pad. addr-selected_protocol get16 dup if 1- copy-protocol-name 7 + then { ext-ALPN-len } \ Adjust ServerHello length to account for the extensions. ext-reneg-len ext-max-frag-len + ext-ALPN-len + dup if 2 + then + write24 \ Protocol version addr-version get16 write16 \ Server random addr-server_random 4 bzero addr-server_random 4 + 28 mkrand addr-server_random 32 write-blob \ Session ID \ TODO: if we have no session cache at all, we might send here \ an empty session ID. This would save a bit of network \ bandwidth. 32 write8 addr-session_id 32 write-blob \ Cipher suite addr-cipher_suite get16 write16 \ Compression method 0 write8 \ Extensions ext-reneg-len ext-max-frag-len + ext-ALPN-len + dup if write16 ext-reneg-len dup if 0xFF01 write16 4 - dup write16 1- addr-saved_finished swap write-blob-head8 else drop then ext-max-frag-len if 0x0001 write16 1 write16 addr-peer_log_max_frag_len get8 8 - write8 then ext-ALPN-len dup if \ Note: the selected protocol name was previously \ copied into the pad. 0x0010 write16 4 - dup write16 2- dup write16 1- addr-pad swap write-blob-head8 else drop then else drop then ; \ Do the first part of ECDHE. Returned value is the computed signature \ length, or a negative error code on error. cc: do-ecdhe-part1 ( curve -- len ) { int curve = T0_POPi(); T0_PUSHi(do_ecdhe_part1(CTX, curve)); } \ Get index of first bit set to 1 (in low to high order). : lowest-1 ( bits -- n ) dup ifnot drop -1 ret then 0 begin dup2 >> 1 and 0= while 1+ repeat swap drop ; \ Write the Server Key Exchange message (if applicable). : write-ServerKeyExchange ( -- ) addr-cipher_suite get16 use-ecdhe? ifnot ret then \ We must select an appropriate curve among the curves that \ are supported both by us and the peer. Right now, we apply \ a fixed preference order: Curve25519, P-256, P-384, P-521, \ then the common curve with the lowest ID. \ (TODO: add some option to make that behaviour configurable.) \ \ This loop always terminates because previous processing made \ sure that ECDHE suites are not selectable if there is no common \ curve. addr-curves get32 dup 0x20000000 and if drop 29 else dup 0x38000000 and dup if swap then drop lowest-1 then { curve-id } \ Compute the signed curve point to send. curve-id do-ecdhe-part1 dup 0< if neg fail then { sig-len } \ If using TLS-1.2+, then the hash function and signature \ algorithm are explicitly encoded in the message. addr-version get16 0x0303 >= { tls1.2+ } 12 write8 sig-len addr-ecdhe_point_len get8 + tls1.2+ 2 and + 6 + write24 \ Curve parameters: named curve with 16-bit ID. 3 write8 curve-id write16 \ Public point. addr-ecdhe_point addr-ecdhe_point_len get8 write-blob-head8 \ If TLS-1.2+, write hash and signature identifiers. tls1.2+ if \ sign_hash_id contains either a hash identifier, \ or the complete 16-bit value to write. addr-sign_hash_id get16 dup 0xFF00 < if write16 else 0xFF and write8 \ 'use-rsa-ecdhe?' returns -1 for RSA, 0 for \ ECDSA. The byte on the wire shall be 1 for RSA, \ 3 for ECDSA. addr-cipher_suite get16 use-rsa-ecdhe? 1 << 3 + write8 then then \ Signature. sig-len write16 addr-pad sig-len write-blob ; \ Get length of the list of anchor names to send to the client. The length \ includes the per-name 2-byte header, but _not_ the 2-byte header for \ the list itself. If no client certificate is requested, then this \ returns 0. cc: ta-names-total-length ( -- len ) { size_t u, len; len = 0; if (CTX->ta_names != NULL) { for (u = 0; u < CTX->num_tas; u ++) { len += CTX->ta_names[u].len + 2; } } else if (CTX->tas != NULL) { for (u = 0; u < CTX->num_tas; u ++) { len += CTX->tas[u].dn.len + 2; } } T0_PUSH(len); } \ Compute length and optionally write the contents of the list of \ supported client authentication methods. : write-list-auth ( do_write -- len ) 0 addr-cipher_suite get16 use-ecdh? if 2+ over if 65 write8 66 write8 then then supports-rsa-sign? if 1+ over if 1 write8 then then supports-ecdsa? if 1+ over if 64 write8 then then swap drop ; : write-signhash-inner2 ( dow algo hashes len id -- dow algo hashes len ) { id } over 1 id << and ifnot ret then 2+ 3 pick if id write8 2 pick write8 then ; : write-signhash-inner1 ( dow algo hashes -- dow len ) 0 4 write-signhash-inner2 5 write-signhash-inner2 6 write-signhash-inner2 3 write-signhash-inner2 2 write-signhash-inner2 -rot 2drop ; \ Compute length and optionally write the contents of the list of \ supported sign+hash algorithms. : write-list-signhash ( do_write -- len ) 0 { len } \ If supporting neither RSA nor ECDSA in the engine, then we \ will do only static ECDH, and thus we claim support for \ everything (for the X.509 validator). supports-rsa-sign? supports-ecdsa? or ifnot 1 0x7C write-signhash-inner1 >len 3 0x7C write-signhash-inner1 len + swap drop ret then supports-rsa-sign? if 1 supported-hash-functions drop write-signhash-inner1 >len then supports-ecdsa? if 3 supported-hash-functions drop write-signhash-inner1 len + >len then drop len ; \ Initialise index for sending the list of anchor DN. cc: begin-ta-name-list ( -- ) { CTX->cur_dn_index = 0; } \ Switch to next DN in the list. Returned value is the DN length, or -1 \ if the end of the list was reached. cc: begin-ta-name ( -- len ) { const br_x500_name *dn; if (CTX->cur_dn_index >= CTX->num_tas) { T0_PUSHi(-1); } else { if (CTX->ta_names == NULL) { dn = &CTX->tas[CTX->cur_dn_index].dn; } else { dn = &CTX->ta_names[CTX->cur_dn_index]; } CTX->cur_dn_index ++; CTX->cur_dn = dn->data; CTX->cur_dn_len = dn->len; T0_PUSH(CTX->cur_dn_len); } } \ Copy a chunk of the current DN into the pad. Returned value is the \ chunk length; this is 0 when the end of the current DN is reached. cc: copy-dn-chunk ( -- len ) { size_t clen; clen = CTX->cur_dn_len; if (clen > sizeof ENG->pad) { clen = sizeof ENG->pad; } memcpy(ENG->pad, CTX->cur_dn, clen); CTX->cur_dn += clen; CTX->cur_dn_len -= clen; T0_PUSH(clen); } \ Write a CertificateRequest message. : write-CertificateRequest ( -- ) \ The list of client authentication types includes: \ rsa_sign (1) \ ecdsa_sign (64) \ rsa_fixed_ecdh (65) \ ecdsa_fixed_ecdh (66) \ rsa_sign and ecdsa_sign require, respectively, RSA and ECDSA \ support. Static ECDH requires that the cipher suite is ECDH. \ When we ask for static ECDH, we always send both rsa_fixed_ecdh \ and ecdsa_fixed_ecdh because what matters there is what the \ X.509 engine may support, and we do not control that. \ \ With TLS 1.2, we must also send a list of supported signature \ and hash algorithms. That list is supposed to qualify both \ the engine itself, and the X.509 validator, which are separate \ in BearSSL. There again, we use the engine capabilities in that \ list, and resort to a generic all-support list if only \ static ECDH is accepted. \ \ (In practice, client implementations tend to have at most one \ or two certificates, and send the chain regardless of what \ algorithms are used in it.) 0 write-list-auth addr-version get16 0x0303 >= if 2+ 0 write-list-signhash + then ta-names-total-length + 3 + \ Message header 13 write8 write24 \ List of authentication methods 0 write-list-auth write8 1 write-list-auth drop \ For TLS 1.2+, list of sign+hash addr-version get16 0x0303 >= if 0 write-list-signhash write16 1 write-list-signhash drop then \ Trust anchor names ta-names-total-length write16 begin-ta-name-list begin begin-ta-name dup 0< if drop ret then write16 begin copy-dn-chunk dup while addr-pad swap write-blob repeat drop again ; \ Write the Server Hello Done message. : write-ServerHelloDone ( -- ) 14 write8 0 write24 ; \ Perform RSA decryption of the client-sent pre-master secret. The value \ is in the pad, and its length is provided as parameter. cc: do-rsa-decrypt ( len prf_id -- ) { int prf_id = T0_POPi(); size_t len = T0_POP(); do_rsa_decrypt(CTX, prf_id, ENG->pad, len); } \ Perform ECDH (not ECDHE). The point from the client is in the pad, and \ its length is provided as parameter. cc: do-ecdh ( len prf_id -- ) { int prf_id = T0_POPi(); size_t len = T0_POP(); do_ecdh(CTX, prf_id, ENG->pad, len); } \ Do the second part of ECDHE. cc: do-ecdhe-part2 ( len prf_id -- ) { int prf_id = T0_POPi(); size_t len = T0_POP(); do_ecdhe_part2(CTX, prf_id, ENG->pad, len); } \ Perform static ECDH. The point from the client is the public key \ extracted from its certificate. cc: do-static-ecdh ( prf_id -- ) { do_static_ecdh(CTX, T0_POP()); } \ Read a ClientKeyExchange header. : read-ClientKeyExchange-header ( -- len ) read-handshake-header 16 = ifnot ERR_UNEXPECTED fail then ; \ Read the Client Key Exchange contents (non-empty case). : read-ClientKeyExchange-contents ( lim -- ) \ What we should get depends on the cipher suite. addr-cipher_suite get16 use-rsa-keyx? if \ RSA key exchange: we expect a RSA-encrypted value. read16 dup 512 > if ERR_LIMIT_EXCEEDED fail then dup { enc-rsa-len } addr-pad swap read-blob enc-rsa-len addr-cipher_suite get16 prf-id do-rsa-decrypt then addr-cipher_suite get16 dup use-ecdhe? swap use-ecdh? { ecdhe ecdh } ecdh ecdhe or if \ ECDH or ECDHE key exchange: we expect an EC point. read8 dup { ec-point-len } addr-pad swap read-blob ec-point-len addr-cipher_suite get16 prf-id ecdhe if do-ecdhe-part2 else do-ecdh then then close-elt ; \ Read the Client Key Exchange (normal case). : read-ClientKeyExchange ( -- ) read-ClientKeyExchange-header read-ClientKeyExchange-contents ; \ Obtain all possible hash values for handshake messages so far. This \ is done because we need the hash value for the CertificateVerify \ _before_ knowing which hash function will actually be used, as this \ information is obtained from decoding the message header itself. \ All hash values are stored in the pad (208 bytes in total). cc: compute-hash-CV ( -- ) { int i; for (i = 1; i <= 6; i ++) { br_multihash_out(&ENG->mhash, i, ENG->pad + HASH_PAD_OFF[i - 1]); } } \ Copy the proper hash value from the pad into the dedicated buffer. \ Returned value is true (-1) on success, false (0) on error (error \ being an unimplemented hash function). The id has already been verified \ to be either 0 (for MD5+SHA-1) or one of the SHA-* functions. cc: copy-hash-CV ( hash_id -- bool ) { int id = T0_POP(); size_t off, len; if (id == 0) { off = 0; len = 36; } else { if (br_multihash_getimpl(&ENG->mhash, id) == 0) { T0_PUSH(0); T0_RET(); } off = HASH_PAD_OFF[id - 1]; len = HASH_PAD_OFF[id] - off; } memcpy(CTX->hash_CV, ENG->pad + off, len); CTX->hash_CV_len = len; CTX->hash_CV_id = id; T0_PUSHi(-1); } \ Verify signature in CertificateVerify. Output is 0 on success, or a \ non-zero error code. cc: verify-CV-sig ( sig-len -- err ) { int err; err = verify_CV_sig(CTX, T0_POP()); T0_PUSHi(err); } \ Process static ECDH. : process-static-ECDH ( ktu -- ) \ Static ECDH is allowed only if the cipher suite uses ECDH, and \ the client's public key has type EC and allows key exchange. \ BR_KEYTYPE_KEYX is 0x10, and BR_KEYTYPE_EC is 2. 0x1F and 0x12 = ifnot ERR_WRONG_KEY_USAGE fail then addr-cipher_suite get16 dup use-ecdh? ifnot ERR_UNEXPECTED fail then prf-id do-static-ecdh ; \ Read CertificateVerify header. : read-CertificateVerify-header ( -- lim ) compute-hash-CV read-handshake-header 15 = ifnot ERR_UNEXPECTED fail then ; \ Read CertificateVerify. The client key type + usage is expected on the \ stack. : read-CertificateVerify ( ktu -- ) \ Check that the key allows for signatures. dup 0x20 and ifnot ERR_WRONG_KEY_USAGE fail then 0x0F and { key-type } \ Get header. read-CertificateVerify-header \ With TLS 1.2+, there is an explicit hash + signature indication, \ which must be compatible with the key type. addr-version get16 0x0303 >= if \ Get hash function, then signature algorithm. The \ signature algorithm is 1 (RSA) or 3 (ECDSA) while our \ symbolic constants for key types are 1 (RSA) or 2 (EC). read16 dup 0xFF and 1+ 1 >> key-type = ifnot ERR_BAD_SIGNATURE fail then 8 >> \ We support only SHA-1, SHA-224, SHA-256, SHA-384 \ and SHA-512. We explicitly reject MD5. dup 2 < over 6 > or if ERR_INVALID_ALGORITHM fail then else \ With TLS 1.0 and 1.1, hash is MD5+SHA-1 (0) for RSA, \ SHA-1 (2) for ECDSA. key-type 0x01 = if 0 else 2 then then copy-hash-CV ifnot ERR_INVALID_ALGORITHM fail then \ Read signature. read16 dup { sig-len } dup 512 > if ERR_LIMIT_EXCEEDED fail then addr-pad swap read-blob sig-len verify-CV-sig dup if fail then drop close-elt ; \ Send a HelloRequest. : send-HelloRequest ( -- ) flush-record begin can-output? not while wait-co drop repeat 22 addr-record_type_out set8 0 write8 0 write24 flush-record 23 addr-record_type_out set8 ; \ Make a handshake. : do-handshake ( initial -- ) 0 addr-application_data set8 22 addr-record_type_out set8 0 addr-selected_protocol set16 multihash-init read-ClientHello more-incoming-bytes? if ERR_UNEXPECTED fail then if \ Session resumption write-ServerHello 0 write-CCS-Finished 0 read-CCS-Finished else \ Not a session resumption write-ServerHello write-Certificate drop write-ServerKeyExchange ta-names-total-length if write-CertificateRequest then write-ServerHelloDone flush-record \ If we sent a CertificateRequest then we expect a \ Certificate message. ta-names-total-length if \ Read client certificate. 0 read-Certificate choice dup 0< uf \ Client certificate validation failed. 2 flag? ifnot neg fail then drop read-ClientKeyExchange read-CertificateVerify-header dup skip-blob drop enduf dup 0= uf \ Client sent no certificate at all. drop 2 flag? ifnot ERR_NO_CLIENT_AUTH fail then read-ClientKeyExchange enduf \ Client certificate was validated. read-ClientKeyExchange-header dup ifnot \ Empty ClientKeyExchange. drop process-static-ECDH else read-ClientKeyExchange-contents read-CertificateVerify then endchoice else \ No client certificate request, we just expect \ a non-empty ClientKeyExchange. read-ClientKeyExchange then 0 read-CCS-Finished 0 write-CCS-Finished save-session then 1 addr-application_data set8 23 addr-record_type_out set8 ; \ Entry point. : main ( -- ! ) \ Perform initial handshake. -1 do-handshake begin \ Wait for further invocation. At that point, we should \ get either an explicit call for renegotiation, or \ an incoming ClientHello handshake message. wait-co dup 0x07 and case 0x00 of 0x10 and if \ The best we can do is ask for a \ renegotiation, then wait for it \ to happen. 0 addr-application_data set8 send-HelloRequest then endof 0x01 of \ Reject renegotiations if the peer does not \ support secure renegotiation, or if the \ "no renegotiation" flag is set. drop addr-reneg get8 1 = 1 flag? or if skip-ClientHello flush-record begin can-output? not while wait-co drop repeat 100 send-warning \ Put back connection in "application \ data" state: it's not dead yet. 1 addr-application_data set8 23 addr-record_type_out set8 else 0 do-handshake then endof ERR_UNEXPECTED fail endcase again ;