主模式第六包：main_inI3_outR3

1. 序言

main_inI3_outR3()函数是ISAKMP协商过程中第六包的核心处理函数的入口，第五六包主要用来验证对方的身份信息，同时此报文也是加密后的报文。这里我们主要说明main_inI3_outR3的函数调用关系、处理流程以及对源码的注释分析，关于main_inI3_outR3的上下文环境暂不叙述，留给后面的文章进行更新。

ISAKMP协商报文的处理流程都比较复杂，此函数在协商的报文处理函数中比较复杂的，因此个人学习期间难免有遗漏和理解错误的地方，请大家多多批评指正。

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目前主要是整理源码中的处理里流程和实现逻辑，尚未深入比较细节的处理；后续在我整理完毕使用主模式协商的9个报文后，我再次结合代码整理每一个报文的详细流程，到时把每一个报文的注意事项、作用，处理方式做一个整体上的把握。同时结合书本上的描述来解释代码层的实现。

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第五六个报文的载荷内容如下：
在这里插入图片描述:

2.函数调用关系

略。

3. 第六个报文流程图

第六个报文的处理流程可以分为三类：

• 解析对方的身份标识(ID)和证书载荷，匹配对方的身份标识
• 身份验证
  • 预共享秘钥
  • 数字证书
• 构建应答报文
  • 身份标识
  • 证书载荷
  • 对数据包进行签名
  • 加密

流程图下图：

4. main_inI3_outR3_tail源码学习

因为main_inI3_outR3中直接调用了main_inI3_outR3_tail, 故而直接将main_inI3_outR3_tail的源代码进行说明，而不再介绍main_inI3_outR3。

该函数的是第六包的核心处理函数，它中调用了main_id_and_auth()完成了对方的ID载荷、证书载荷等的解析和认证工作。

在认证成功的前提下，在继续构建自已的应答报文，将自己的身份标识、证书、签名值等载荷封装然后对报文进行加密，最后发送给隧道的发起者。

static stf_status
main_inI3_outR3_tail(struct msg_digest *md
, struct key_continuation *kc)
{struct state *const st = md->st;u_int8_t auth_payload;pb_stream r_id_pbs;	/* ID Payload; also used for hash calculation */cert_t mycert;bool send_cert;unsigned int np;/* ID and HASH_I or SIG_I in* Note: this may switch the connection being used!*/{stf_status r = main_id_and_auth(md, FALSE, main_inI3_outR3_continue, kc);if (r != STF_OK)return r;}/* send certificate if we have one and auth is RSA */mycert = st->st_connection->spd.this.cert;send_cert = st->st_oakley.auth == OAKLEY_RSA_SIG&& mycert.type != CERT_NONE&& ((st->st_connection->spd.this.sendcert == cert_sendifasked&& st->hidden_variables.st_got_certrequest)|| st->st_connection->spd.this.sendcert==cert_alwayssend);doi_log_cert_thinking(md, st->st_oakley.auth, mycert.type, st->st_connection->spd.this.sendcert, st->hidden_variables.st_got_certrequest, send_cert);/*************** build output packet HDR*;IDir;HASH/SIG_R ***************//* proccess_packet() would automatically generate the HDR** payload if smc->first_out_payload is not ISAKMP_NEXT_NONE.* We don't do this because we wish there to be no partially* built output packet if we need to suspend for asynch DNS.*//* ??? NOTE: this is almost the same as main_inR2_outI3's code *//* HDR* out* If auth were PKE_AUTH or RPKE_AUTH, ISAKMP_NEXT_HASH would* be first payload.*/echo_hdr(md, TRUE, ISAKMP_NEXT_ID);/*回转数据包头;*/auth_payload = st->st_oakley.auth == OAKLEY_PRESHARED_KEY? ISAKMP_NEXT_HASH : ISAKMP_NEXT_SIG;/* IDir out *//*添加ID载荷*/{/* id_hd should be struct isakmp_id, but struct isakmp_ipsec_id* allows build_id_payload() to work for both phases.*/struct isakmp_ipsec_id id_hd;chunk_t id_b;build_id_payload(&id_hd, &id_b, &st->st_connection->spd.this);id_hd.isaiid_np = (send_cert)? ISAKMP_NEXT_CERT : auth_payload;if (!out_struct(&id_hd, &isakmp_ipsec_identification_desc, &md->rbody, &r_id_pbs)/*添加头部*/|| !out_chunk(id_b, &r_id_pbs, "my identity"))/*添加ID内容*/return STF_INTERNAL_ERROR;close_output_pbs(&r_id_pbs);}/* CERT out, if we have one */if (send_cert)/*添加证书载荷*/{pb_stream cert_pbs;struct isakmp_cert cert_hd;cert_hd.isacert_np = ISAKMP_NEXT_SIG;cert_hd.isacert_type = mycert.type;openswan_log("I am sending my cert");/*添加证书头部描述*/if (!out_struct(&cert_hd, &isakmp_ipsec_certificate_desc, &md->rbody, &cert_pbs))return STF_INTERNAL_ERROR;/*添加证书主体内容*/if (!out_chunk(get_mycert(mycert), &cert_pbs, "CERT"))return STF_INTERNAL_ERROR;close_output_pbs(&cert_pbs);}#ifdef TPM{pb_stream *pbs = &md->rbody;size_t enc_len = pbs_offset(pbs) - sizeof(struct isakmp_hdr);TCLCALLOUT_crypt("preHash", st,pbs,sizeof(struct isakmp_hdr),enc_len);/* find location of ID PBS */tpm_findID(pbs, &r_id_pbs);}
#endif/* IKEv2 NOTIFY payload */np = ISAKMP_NEXT_NONE;if(st->st_connection->policy & POLICY_IKEV2_ALLOW) {np = ISAKMP_NEXT_VID;}/* HASH_R or SIG_R out */{u_char hash_val[MAX_DIGEST_LEN];/*计算ID载荷的hash值*/size_t hash_len = main_mode_hash(st, hash_val, FALSE, &r_id_pbs);if (auth_payload == ISAKMP_NEXT_HASH)/*如果采用hash进制认证*/{/* HASH_R out *//*填充哈希值*/if (!out_generic_raw(np, &isakmp_hash_desc, &md->rbody, hash_val, hash_len, "HASH_R"))return STF_INTERNAL_ERROR;}else/*在哈希的基础上再进行一个签名采用签名进制认证*/{/* SIG_R out */u_char sig_val[RSA_MAX_OCTETS];size_t sig_len = RSA_sign_hash(st->st_connection, sig_val, hash_val, hash_len);if (sig_len == 0){loglog(RC_LOG_SERIOUS, "unable to locate my private key for RSA Signature");return STF_FAIL + AUTHENTICATION_FAILED;}if (!out_generic_raw(np, &isakmp_signature_desc/*填充签名签名信息*/, &md->rbody, sig_val, sig_len, "SIG_R"))return STF_INTERNAL_ERROR;}}if(st->st_connection->policy & POLICY_IKEV2_ALLOW) {if(!out_vid(ISAKMP_NEXT_NONE, &md->rbody, VID_MISC_IKEv2))return STF_INTERNAL_ERROR;}/* encrypt message, sans fixed part of header */if (!encrypt_message(&md->rbody, st))return STF_INTERNAL_ERROR;	/* ??? we may be partly committed *//* Last block of Phase 1 (R3), kept for Phase 2 IV generation */DBG_cond_dump(DBG_CRYPT, "last encrypted block of Phase 1:", st->st_new_iv, st->st_new_iv_len);
/*保存第一阶段的IV信息*/st->st_ph1_iv_len = st->st_new_iv_len;set_ph1_iv(st, st->st_new_iv);/*设置初始化向量*//* It seems as per Cisco implementation, XAUTH and MODECFG* are not supposed to be performed again during rekey */if( st->st_connection->remotepeertype == CISCO &&st->st_connection->newest_isakmp_sa != SOS_NOBODY &&st->st_connection->spd.this.xauth_client) {DBG(DBG_CONTROL, DBG_log("Skipping XAUTH for rekey for Cisco Peer compatibility."));st->hidden_variables.st_xauth_client_done = TRUE;st->st_oakley.xauth = 0;if(st->st_connection->spd.this.modecfg_client) {DBG(DBG_CONTROL, DBG_log("Skipping ModeCFG for rekey for Cisco Peer compatibility."));st->hidden_variables.st_modecfg_vars_set = TRUE;st->hidden_variables.st_modecfg_started = TRUE;}}ISAKMP_SA_established(st->st_connection, st->st_serialno);/* ??? If st->st_connectionc->gw_info != NULL,* we should keep the public key -- it tested out.*/return STF_OK;
}

5. oakley_id_and_auth源码学习

oakley_id_and_auth()函数的作用是对第五包中的身份标识、证书载荷、证书请求载荷等进行解析，并根据配置的认证方式(预共享秘钥、数字证书)完成对对端的认证。

stf_status
oakley_id_and_auth(struct msg_digest *md, bool initiator	/* are we the Initiator? */, bool aggrmode                /* aggressive mode? */, cont_fn_t cont_fn	/* continuation function */, const struct key_continuation *kc	/* current state, can be NULL */
){struct state *st = md->st;u_char hash_val[MAX_DIGEST_LEN];size_t hash_len;stf_status r = STF_OK;/* if we are already processing a packet on this st, we will be unable* to start another crypto operation below */if (is_suspended(st)) {/*当前有数据包正在处理*/openswan_log("%s: already processing a suspended cyrpto operation ""on this SA, duplicate will be dropped.", __func__);return STF_TOOMUCHCRYPTO;}
//1 HDR*, IDii, [ CERT, ] SIG_I /* ID Payload in.* Note: this may switch the connection being used!*//*主动模式时，需要解析对端标识信息;*/if (!aggrmode && !decode_peer_id(md, initiator, FALSE))return STF_FAIL + INVALID_ID_INFORMATION;
/*对报文进行验签: 1.计算对端ID的哈希值2. 如果使用的共享秘钥，则报文中使用hash算法进行签名，因此直接比较哈希值是否一致即可3. 如果使用证书的方式，则需要使用RSA....等进行验签
*//* Hash the ID Payload.* main_mode_hash requires idpl->cur to be at end of payload* so we temporarily set if so.*/{pb_stream *idpl = &md->chain[ISAKMP_NEXT_ID]->pbs;u_int8_t *old_cur = idpl->cur;idpl->cur = idpl->roof;hash_len = main_mode_hash(st, hash_val, !initiator, idpl);idpl->cur = old_cur;}switch (st->st_oakley.auth){case OAKLEY_PRESHARED_KEY:/*共享秘钥认证*/{pb_stream *const hash_pbs = &md->chain[ISAKMP_NEXT_HASH]->pbs;/*获取哈希载荷的数据部分(即哈希值)*/if (pbs_left(hash_pbs) != hash_len|| memcmp(hash_pbs->cur, hash_val, hash_len) != 0){DBG_cond_dump(DBG_CRYPT, "received HASH:", hash_pbs->cur, pbs_left(hash_pbs));loglog(RC_LOG_SERIOUS, "received Hash Payload does not match computed value");/* XXX Could send notification back */r = STF_FAIL + INVALID_HASH_INFORMATION;}}break;case OAKLEY_RSA_SIG:/*数字证书认证*/r = RSA_check_signature(st, hash_val, hash_len, &md->chain[ISAKMP_NEXT_SIG]->pbs
#ifdef USE_KEYRR, kc == NULL? NULL : kc->ac.keys_from_dns
#endif /* USE_KEYRR */, kc == NULL? NULL : kc->ac.gateways_from_dns);if (r == STF_SUSPEND){/* initiate/resume asynchronous DNS lookup for key */struct key_continuation *nkc= alloc_thing(struct key_continuation, "key continuation");enum key_oppo_step step_done = kc == NULL? kos_null : kc->step;err_t ugh;/* Record that state is used by a suspended md */passert(st->st_suspended_md == NULL);set_suspended(st,md);nkc->failure_ok = FALSE;nkc->md = md;switch (step_done){case kos_null:/* first try: look for the TXT records */nkc->step = kos_his_txt;
#ifdef USE_KEYRRnkc->failure_ok = TRUE;
#endifugh = start_adns_query(&st->st_connection->spd.that.id, &st->st_connection->spd.that.id	/* SG itself */, ns_t_txt, cont_fn, &nkc->ac);break;#ifdef USE_KEYRRcase kos_his_txt:/* second try: look for the KEY records */nkc->step = kos_his_key;ugh = start_adns_query(&st->st_connection->spd.that.id, NULL	/* no sgw for KEY */, ns_t_key, cont_fn, &nkc->ac);break;
#endif /* USE_KEYRR */default:bad_case(step_done);}if (ugh != NULL){report_key_dns_failure(&st->st_connection->spd.that.id, ugh);set_suspended(st, NULL);r = STF_FAIL + INVALID_KEY_INFORMATION;} else {/** since this state is waiting for a DNS query, delete* any events that might kill it.*/delete_event(st);}}break;default:bad_case(st->st_oakley.auth);}if (r == STF_OK)DBG(DBG_CRYPT, DBG_log("authentication succeeded"));return r;
}