. 单台Linux CentOS7.2系统，安装一个EMQTTD的实例broker。

. emq的版本2.3.11。

. 客户端分为mosquitto_pub，以及MQTT.fx 1.7.1的subscriber。

. 证书是通过openssl（version：1.0.2k-fips）生成的，rootCA是自签名的，subscriber和publisher的证书是通过rootCA签署的。

. 抓包工具wireshark（version: 2.6.,下载地址https://www.wireshark.org/download/win64/），分析SSL/TLS通信的消息流.

C->S: Client Hello

S->C: Server Hello

S->C: Certificate,Server Key Exchange, Certificate Request, Server Hello Done

C->S: Certificate, Client Key Exchange

C->S: Certificate Verify,Change Cipher Spec,Encrypted Handshake Message

S->C: Change Cipher Spec,Encrypted Handshake Message

C->S: Application Data

S->C: Application Data

). certificate Verify消息必须在client key exchange后面由客户端发出去给服务器端。

). 这个消息，是客户端构建的，内容是客户端收发的所有的handshake消息（不含当前这个Verify的消息）拼接后的内容进行hash，然后用证书对应的私钥进行签名后所得的内容S1。

). 这个消息，服务端会进行验证。验证的逻辑，通过对服务端缓存的客户端消息，以及服务端发送的所有handshake消息，同样进行拼接然后计算hash值h2，用客户端的证书中的公钥解析Verify中的签名S1得到对应的hash值h1，对比h1和和

，若相同，则验证通过，否则失败。

## Path to the file containing the user's private PEM-encoded key.

##

## See: http://erlang.org/doc/man/ssl.html

##

## Value: File

#listener.ssl.external.keyfile = /etc/emqttd/certs/key.pem

listener.ssl.external.keyfile = /opt/certs/server.key

## Path to a file containing the user certificate.

##

## See: http://erlang.org/doc/man/ssl.html

##

## Value: File

#listener.ssl.external.certfile = /etc/emqttd/certs/cert.pem

listener.ssl.external.certfile = /opt/certs/server.crt

## Path to the file containing PEM-encoded CA certificates. The CA certificates

## are used during server authentication and when building the client certificate chain.

##

## Value: File

## listener.ssl.external.cacertfile = /etc/emqttd/certs/cacert.pem

listener.ssl.external.cacertfile = /opt/certs/rootCA.crt

## The Ephemeral Diffie-Helman key exchange is a very effective way of

## ensuring Forward Secrecy by exchanging a set of keys that never hit

## the wire. Since the DH key is effectively signed by the private key,

## it needs to be at least as strong as the private key. In addition,

## the default DH groups that most of the OpenSSL installations have

## are only a handful (since they are distributed with the OpenSSL

## package that has been built for the operating system it’s running on)

## and hence predictable (not to mention,  bits only).

## In order to escape this situation, first we need to generate a fresh,

## strong DH group, store it in a file and then use the option above,

## to force our SSL application to use the new DH group. Fortunately,

## OpenSSL provides us with a tool to do that. Simply run:

## openssl dhparam -out dh-params.pem

##

## Value: File

## listener.ssl.external.dhfile = /etc/emqttd/certs/dh-params.pem

## A server only does x509-path validation in mode verify_peer,

## as it then sends a certificate request to the client (this

## message is not sent if the verify option is verify_none).

## You can then also want to specify option fail_if_no_peer_cert.

## More information at: http://erlang.org/doc/man/ssl.html

##

## Value: verify_peer | verify_none

listener.ssl.external.verify = verify_none    #主要是在双向验证的基础上将此配置改为verify_none

## Used together with {verify, verify_peer} by an SSL server. If set to true,

## the server fails if the client does not have a certificate to send, that is,

## sends an empty certificate.

##

## Value: true | false

## listener.ssl.external.fail_if_no_peer_cert = true

C->S: Client Hello

S->C: Server Hello

S->C: Certificate, Server Key Exchange, Server Hello Done

C->S: Client Key Exchange

C->S: Change Cipher Spec, Encrypted Handshake Message

S->C: Change Cipher Spec, Encrypted Handshake Message

C->S: Application Data

S->C: Application Data

......

S->C: Encrypted Alert

C->S: Encrypted Alert