/* * libwebsockets - small server side websockets and web server implementation * * Copyright (C) 2010 - 2019 Andy Green * * 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. */ #include "private-lib-core.h" #include "private-lib-jose-jwe.h" /* * From RFC7518 JWA * * 4.6. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static * (ECDH-ES) * * This section defines the specifics of key agreement with Elliptic * Curve Diffie-Hellman Ephemeral Static [RFC6090], in combination with * the Concat KDF, as defined in Section 5.8.1 of [NIST.800-56A]. The * key agreement result can be used in one of two ways: * * 1. directly as the Content Encryption Key (CEK) for the "enc" * algorithm, in the Direct Key Agreement mode, or * * 2. as a symmetric key used to wrap the CEK with the "A128KW", * "A192KW", or "A256KW" algorithms, in the Key Agreement with Key * Wrapping mode. * * A new ephemeral public key value MUST be generated for each key * agreement operation. * * In Direct Key Agreement mode, the output of the Concat KDF MUST be a * key of the same length as that used by the "enc" algorithm. In this * case, the empty octet sequence is used as the JWE Encrypted Key * value. The "alg" (algorithm) Header Parameter value "ECDH-ES" is * used in the Direct Key Agreement mode. * * In Key Agreement with Key Wrapping mode, the output of the Concat KDF * MUST be a key of the length needed for the specified key wrapping * algorithm. In this case, the JWE Encrypted Key is the CEK wrapped * with the agreed-upon key. * * The following "alg" (algorithm) Header Parameter values are used to * indicate that the JWE Encrypted Key is the result of encrypting the * CEK using the result of the key agreement algorithm as the key * encryption key for the corresponding key wrapping algorithm: * * +-----------------+-------------------------------------------------+ * | "alg" Param | Key Management Algorithm | * | Value | | * +-----------------+-------------------------------------------------+ * | ECDH-ES+A128KW | ECDH-ES using Concat KDF and CEK wrapped with | * | | "A128KW" | * | ECDH-ES+A192KW | ECDH-ES using Concat KDF and CEK wrapped with | * | | "A192KW" | * | ECDH-ES+A256KW | ECDH-ES using Concat KDF and CEK wrapped with | * | | "A256KW" | * +-----------------+-------------------------------------------------+ * * 4.6.1. Header Parameters Used for ECDH Key Agreement * * The following Header Parameter names are used for key agreement as * defined below. * * 4.6.1.1. "epk" (Ephemeral Public Key) Header Parameter * * The "epk" (ephemeral public key) value created by the originator for * the use in key agreement algorithms. This key is represented as a * JSON Web Key [JWK] public key value. It MUST contain only public key * parameters and SHOULD contain only the minimum JWK parameters * necessary to represent the key; other JWK parameters included can be * checked for consistency and honored, or they can be ignored. This * Header Parameter MUST be present and MUST be understood and processed * by implementations when these algorithms are used. * * 4.6.1.2. "apu" (Agreement PartyUInfo) Header Parameter * * The "apu" (agreement PartyUInfo) value for key agreement algorithms * using it (such as "ECDH-ES"), represented as a base64url-encoded * string. When used, the PartyUInfo value contains information about * the producer. Use of this Header Parameter is OPTIONAL. This Header * Parameter MUST be understood and processed by implementations when * these algorithms are used. * * 4.6.1.3. "apv" (Agreement PartyVInfo) Header Parameter * * The "apv" (agreement PartyVInfo) value for key agreement algorithms * using it (such as "ECDH-ES"), represented as a base64url encoded * string. When used, the PartyVInfo value contains information about * the recipient. Use of this Header Parameter is OPTIONAL. This * Header Parameter MUST be understood and processed by implementations * when these algorithms are used. * * 4.6.2. Key Derivation for ECDH Key Agreement * * The key derivation process derives the agreed-upon key from the * shared secret Z established through the ECDH algorithm, per * Section 6.2.2.2 of [NIST.800-56A]. * * Key derivation is performed using the Concat KDF, as defined in * Section 5.8.1 of [NIST.800-56A], where the Digest Method is SHA-256. * The Concat KDF parameters are set as follows: * * Z * This is set to the representation of the shared secret Z as an * octet sequence. * * keydatalen * This is set to the number of bits in the desired output key. For * "ECDH-ES", this is length of the key used by the "enc" algorithm. * For "ECDH-ES+A128KW", "ECDH-ES+A192KW", and "ECDH-ES+A256KW", this * is 128, 192, and 256, respectively. * * AlgorithmID * The AlgorithmID value is of the form Datalen || Data, where Data * is a variable-length string of zero or more octets, and Datalen is * a fixed-length, big-endian 32-bit counter that indicates the * length (in octets) of Data. In the Direct Key Agreement case, * Data is set to the octets of the ASCII representation of the "enc" * Header Parameter value. In the Key Agreement with Key Wrapping * case, Data is set to the octets of the ASCII representation of the * "alg" (algorithm) Header Parameter value. * * PartyUInfo * The PartyUInfo value is of the form Datalen || Data, where Data is * a variable-length string of zero or more octets, and Datalen is a * fixed-length, big-endian 32-bit counter that indicates the length * (in octets) of Data. If an "apu" (agreement PartyUInfo) Header * Parameter is present, Data is set to the result of base64url * decoding the "apu" value and Datalen is set to the number of * octets in Data. Otherwise, Datalen is set to 0 and Data is set to * the empty octet sequence. * * PartyVInfo * The PartyVInfo value is of the form Datalen || Data, where Data is * a variable-length string of zero or more octets, and Datalen is a * fixed-length, big-endian 32-bit counter that indicates the length * (in octets) of Data. If an "apv" (agreement PartyVInfo) Header * Parameter is present, Data is set to the result of base64url * decoding the "apv" value and Datalen is set to the number of * octets in Data. Otherwise, Datalen is set to 0 and Data is set to * the empty octet sequence. * * SuppPubInfo * This is set to the keydatalen represented as a 32-bit big-endian * integer. * * SuppPrivInfo * This is set to the empty octet sequence. * * Applications need to specify how the "apu" and "apv" Header * Parameters are used for that application. The "apu" and "apv" values * MUST be distinct, when used. Applications wishing to conform to * [NIST.800-56A] need to provide values that meet the requirements of * that document, e.g., by using values that identify the producer and * consumer. Alternatively, applications MAY conduct key derivation in * a manner similar to "Diffie-Hellman Key Agreement Method" [RFC2631]: * in that case, the "apu" parameter MAY either be omitted or represent * a random 512-bit value (analogous to PartyAInfo in Ephemeral-Static * mode in RFC 2631) and the "apv" parameter SHOULD NOT be present. * */ /* * - ECDH-ES[-variant] comes in the jose "alg" and just covers key agreement. * The "enc" action is completely separate and handled elsewhere. However * the key size throughout is determined by the needs of the "enc" action. * * - The jwe->jws.jwk is the PEER - the encryption consumer's - public key. * * - The public part of the ephemeral key comes out in jose.jwk_ephemeral * * - Return shared secret length or < 0 for error * * - Unwrapped CEK in EKEY. If any, wrapped CEK in "wrapped". * * - Caller responsibility to cleanse EKEY. */ static int lws_jwe_encrypt_ecdh(struct lws_jwe *jwe, char *temp, int *temp_len, uint8_t *cek) { uint8_t shared_secret[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES], derived[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES]; int m, n, ret = -1, ot = *temp_len, ss_len = sizeof(shared_secret), // kw_hlen = lws_genhash_size(jwe->jose.alg->hash_type), enc_hlen = lws_genhmac_size(jwe->jose.enc_alg->hmac_type), ekbytes = 32; //jwe->jose.alg->keybits_fixed / 8; struct lws_genec_ctx ecctx; struct lws_jwk *ephem = &jwe->jose.recipient[jwe->recip].jwk_ephemeral; if (jwe->jws.jwk->kty != LWS_GENCRYPTO_KTY_EC) { lwsl_err("%s: unexpected kty %d\n", __func__, jwe->jws.jwk->kty); return -1; } ephem->kty = LWS_GENCRYPTO_KTY_EC; ephem->private_key = 1; /* Generate jose.jwk_ephemeral on the peer public key curve */ if (lws_genecdh_create(&ecctx, jwe->jws.context, NULL)) goto bail; /* ephemeral context gets random key on same curve as recip pubkey */ if (lws_genecdh_new_keypair(&ecctx, LDHS_OURS, (const char *) jwe->jws.jwk->e[LWS_GENCRYPTO_EC_KEYEL_CRV].buf, ephem->e)) goto bail; /* peer context gets js->jwk key */ if (lws_genecdh_set_key(&ecctx, jwe->jws.jwk->e, LDHS_THEIRS)) { lwsl_err("%s: setting peer pubkey failed\n", __func__); goto bail; } /* combine our ephemeral key and the peer pubkey to get the secret */ if (lws_genecdh_compute_shared_secret(&ecctx, shared_secret, &ss_len)) { lwsl_notice("%s: lws_genecdh_compute_shared_secret failed\n", __func__); goto bail; } /* * The private part of the ephemeral key is finished with... * cleanse and free it. We need to keep the public part around so we * can publish it with the JWE as "epk". */ lws_explicit_bzero(ephem->e[LWS_GENCRYPTO_EC_KEYEL_D].buf, ephem->e[LWS_GENCRYPTO_EC_KEYEL_D].len); lws_free_set_NULL(ephem->e[LWS_GENCRYPTO_EC_KEYEL_D].buf); ephem->e[LWS_GENCRYPTO_EC_KEYEL_D].len = 0; ephem->private_key = 0; /* * Derive the CEK from the shared secret... amount of bytes written to * derived matches bitcount in jwe->jose.enc_alg->keybits_fixed * * In Direct Key Agreement mode, the output of the Concat KDF MUST be a * key of the same length as that used by the "enc" algorithm. */ if (lws_jwa_concat_kdf(jwe, jwe->jose.alg->algtype_crypto == LWS_JOSE_ENCTYPE_NONE, derived, shared_secret, ss_len)) { lwsl_notice("%s: lws_jwa_concat_kdf failed\n", __func__); goto bail; } /* in P-521 case, we get a 66-byte shared secret for a 64-byte key */ if (ss_len < enc_hlen) { lwsl_err("%s: concat KDF bad derived key len %d\n", __func__, ss_len); goto bail; } /* * For "ECDH-ES", that was it, and we use what we just wrapped in * wrapped as the CEK without publishing it. * * For "ECDH-ES-AES[128,192,256]KW", we generate a new, random CEK and * then wrap it using the key we just wrapped, and make the wrapped * version available in EKEY. */ if (jwe->jose.alg->algtype_crypto != LWS_JOSE_ENCTYPE_NONE) { struct lws_gencrypto_keyelem el; struct lws_genaes_ctx aesctx; /* generate the actual CEK in cek */ if (lws_get_random(jwe->jws.context, cek, enc_hlen) != (size_t)enc_hlen) { lwsl_err("Problem getting random\n"); goto bail; } /* wrap with the derived key */ el.buf = derived; el.len = enc_hlen / 2; if (lws_genaes_create(&aesctx, LWS_GAESO_ENC, LWS_GAESM_KW, &el, 1, NULL)) { lwsl_notice("%s: lws_genaes_create\n", __func__); goto bail; } /* wrap CEK into EKEY */ n = lws_genaes_crypt(&aesctx, cek, enc_hlen, (void *)jwe->jws.map.buf[LJWE_EKEY], NULL, NULL, NULL, 0); m = lws_genaes_destroy(&aesctx, NULL, 0); if (n < 0) { lwsl_err("%s: encrypt cek fail\n", __func__); goto bail; } if (m < 0) { lwsl_err("%s: lws_genaes_destroy fail\n", __func__); goto bail; } jwe->jws.map.len[LJWE_EKEY] = enc_hlen + 8; /* Wrapped CEK is in EKEY. Random CEK is in cek. */ } else /* direct derived CEK is in cek */ memcpy(cek, derived, enc_hlen); /* rewrite the protected JOSE header to have the epk pieces */ jwe->jws.map.buf[LJWE_JOSE] = temp; m = n = lws_snprintf(temp, *temp_len, "{\"alg\":\"%s\", \"enc\":\"%s\", \"epk\":", jwe->jose.alg->alg, jwe->jose.enc_alg->alg); *temp_len -= n; n = lws_jwk_export(ephem, 0, temp + (ot - *temp_len), temp_len); if (n < 0) { lwsl_err("%s: ephemeral export failed\n", __func__); goto bail; } m += n; n = lws_snprintf(temp + (ot - *temp_len), *temp_len, "}"); *temp_len -= n + 1; m += n; jwe->jws.map.len[LJWE_JOSE] = m; /* create a b64 version of the JOSE header, needed later for AAD */ if (lws_jws_encode_b64_element(&jwe->jws.map_b64, LJWE_JOSE, temp + (ot - *temp_len), temp_len, jwe->jws.map.buf[LJWE_JOSE], jwe->jws.map.len[LJWE_JOSE])) return -1; ret = enc_hlen; bail: lws_genec_destroy(&ecctx); /* cleanse the shared secret (watch out for cek at parent too) */ lws_explicit_bzero(shared_secret, ekbytes); lws_explicit_bzero(derived, ekbytes); return ret; } int lws_jwe_encrypt_ecdh_cbc_hs(struct lws_jwe *jwe, char *temp, int *temp_len) { int ss_len, // kw_hlen = lws_genhash_size(jwe->jose.alg->hash_type), enc_hlen = lws_genhmac_size(jwe->jose.enc_alg->hmac_type); uint8_t cek[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES]; int ekbytes = jwe->jose.alg->keybits_fixed / 8; int n, ot = *temp_len, ret = -1; /* if we will produce an EKEY, make space for it */ if (jwe->jose.alg->algtype_crypto != LWS_JOSE_ENCTYPE_NONE) { if (lws_jws_alloc_element(&jwe->jws.map, LJWE_EKEY, temp + (ot - *temp_len), temp_len, enc_hlen + 8, 0)) goto bail; } /* decrypt the CEK */ ss_len = lws_jwe_encrypt_ecdh(jwe, temp + (ot - *temp_len), temp_len, cek); if (ss_len < 0) { lwsl_err("%s: lws_jwe_encrypt_ecdh failed\n", __func__); return -1; } /* cek contains the unwrapped CEK. EKEY may contain wrapped CEK */ /* make space for the payload encryption pieces */ if (lws_jws_alloc_element(&jwe->jws.map, LJWE_ATAG, temp + (ot - *temp_len), temp_len, enc_hlen / 2, 0)) goto bail; if (lws_jws_alloc_element(&jwe->jws.map, LJWE_IV, temp + (ot - *temp_len), temp_len, LWS_JWE_AES_IV_BYTES, 0)) goto bail; /* Perform the authenticated encryption on CTXT... * ...the AAD is b64u(protected JOSE header) */ n = lws_jwe_encrypt_cbc_hs(jwe, cek, (uint8_t *)jwe->jws.map_b64.buf[LJWE_JOSE], jwe->jws.map_b64.len[LJWE_JOSE]); if (n < 0) { lwsl_notice("%s: lws_jwe_encrypt_cbc_hs failed\n", __func__); goto bail; } ret = 0; bail: /* if fail or direct CEK, cleanse and remove EKEY */ if (ret || jwe->jose.enc_alg->algtype_crypto == LWS_JOSE_ENCTYPE_NONE) { if (jwe->jws.map.len[LJWE_EKEY]) lws_explicit_bzero((void *)jwe->jws.map.buf[LJWE_EKEY], jwe->jws.map.len[LJWE_EKEY]); jwe->jws.map.len[LJWE_EKEY] = 0; } lws_explicit_bzero(cek, ekbytes); return ret; } /* * jwe->jws.jwk is recipient private key * * If kw mode, then EKEY is the wrapped CEK * * */ static int lws_jwe_auth_and_decrypt_ecdh(struct lws_jwe *jwe) { uint8_t shared_secret[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES], derived[LWS_JWE_LIMIT_KEY_ELEMENT_BYTES]; int ekbytes = jwe->jose.enc_alg->keybits_fixed / 8, enc_hlen = lws_genhmac_size(jwe->jose.enc_alg->hmac_type); struct lws_genec_ctx ecctx; int n, ret = -1, ss_len = sizeof(shared_secret); if (jwe->jws.jwk->kty != LWS_GENCRYPTO_KTY_EC) { lwsl_err("%s: unexpected kty %d\n", __func__, jwe->jws.jwk->kty); return -1; } if (jwe->jose.recipient[jwe->recip].jwk_ephemeral.kty != LWS_GENCRYPTO_KTY_EC) { lwsl_err("%s: missing epk\n", __func__); return -1; } /* * Recompute the shared secret... * * - direct: it's the CEK * * - aeskw: apply it as AES keywrap to EKEY to get the CEK */ /* Generate jose.jwk_ephemeral on the peer public key curve */ if (lws_genecdh_create(&ecctx, jwe->jws.context, NULL)) goto bail; /* Load our private key into our side of the ecdh context */ if (lws_genecdh_set_key(&ecctx, jwe->jws.jwk->e, LDHS_OURS)) { lwsl_err("%s: setting our private key failed\n", __func__); goto bail; } /* Import the ephemeral public key into the peer side */ if (lws_genecdh_set_key(&ecctx, jwe->jose.recipient[jwe->recip].jwk_ephemeral.e, LDHS_THEIRS)) { lwsl_err("%s: setting epk pubkey failed\n", __func__); goto bail; } /* combine their ephemeral key and our private key to get the secret */ if (lws_genecdh_compute_shared_secret(&ecctx, shared_secret, &ss_len)) { lwsl_notice("%s: lws_genecdh_compute_shared_secret failed\n", __func__); goto bail; } lws_genec_destroy(&ecctx); if (ss_len < enc_hlen) { lwsl_err("%s: ss_len %d ekbytes %d\n", __func__, ss_len, enc_hlen); goto bail; } /* * Derive the CEK from the shared secret... amount of bytes written to * cek[] matches bitcount in jwe->jose.enc_alg->keybits_fixed */ if (lws_jwa_concat_kdf(jwe, jwe->jose.alg->algtype_crypto == LWS_JOSE_ENCTYPE_NONE, derived, shared_secret, ss_len)) { lwsl_notice("%s: lws_jwa_concat_kdf failed\n", __func__); goto bail; } /* * "ECDH-ES": derived is the CEK * "ECDH-ES-AES[128,192,256]KW": wrapped key is in EKEY, * "derived" contains KEK */ if (jwe->jose.alg->algtype_crypto != LWS_JOSE_ENCTYPE_NONE) { struct lws_gencrypto_keyelem el; struct lws_genaes_ctx aesctx; int m; /* Confirm space for EKEY */ if (jwe->jws.map.len[LJWE_EKEY] < (unsigned int)enc_hlen) { lwsl_err("%s: missing EKEY\n", __func__); goto bail; } /* unwrap with the KEK we derived */ el.buf = derived; el.len = enc_hlen / 2; if (lws_genaes_create(&aesctx, LWS_GAESO_DEC, LWS_GAESM_KW, &el, 1, NULL)) { lwsl_notice("%s: lws_genaes_create\n", __func__); goto bail; } /* decrypt the EKEY to end up with CEK in "shared_secret" */ n = lws_genaes_crypt(&aesctx, (const uint8_t *)jwe->jws.map.buf[LJWE_EKEY], jwe->jws.map.len[LJWE_EKEY], (uint8_t *)shared_secret, NULL, NULL, NULL, 0); m = lws_genaes_destroy(&aesctx, NULL, 0); if (n < 0) { lwsl_err("%s: decrypt cek fail\n", __func__); goto bail; } if (m < 0) { lwsl_err("%s: lws_genaes_destroy fail\n", __func__); goto bail; } } else memcpy(shared_secret, derived, enc_hlen); /* either way, the recovered CEK is in shared_secret */ if (lws_jwe_auth_and_decrypt_cbc_hs(jwe, shared_secret, (uint8_t *)jwe->jws.map_b64.buf[LJWE_JOSE], jwe->jws.map_b64.len[LJWE_JOSE]) < 0) { lwsl_err("%s: lws_jwe_auth_and_decrypt_cbc_hs fail\n", __func__); goto bail; } /* if all went well, then CTXT is now the plaintext */ ret = 0; bail: /* cleanse wrapped on stack that contained the CEK / wrapped key */ lws_explicit_bzero(derived, ekbytes); /* cleanse the shared secret */ lws_explicit_bzero(shared_secret, ekbytes); return ret; } int lws_jwe_auth_and_decrypt_ecdh_cbc_hs(struct lws_jwe *jwe, char *temp, int *temp_len) { /* create a b64 version of the JOSE header, needed later for AAD */ if (lws_jws_encode_b64_element(&jwe->jws.map_b64, LJWE_JOSE, temp, temp_len, jwe->jws.map.buf[LJWE_JOSE], jwe->jws.map.len[LJWE_JOSE])) return -1; return lws_jwe_auth_and_decrypt_ecdh(jwe); }