MQTT研究之EMQ：【SSL双向验证】

EMQ是当前MQTT中，用于物联网领域中比较出色的一个broker，今天我这里要记录和分享的是关于SSL安全通信的配置和注意细节。

环境：

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

2. emq的版本2.3.11。

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

4. 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。

1、CA根证书的生成

[root@ws3 certs]# openssl req -x509 -new -days 3650 -keyout ca.key -out rootCA.crt -nodes
Generating a  bit RSA private key
.....................+++
.........................................................................................................................+++
writing new private key to 'ca.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name ( letter code) [XX]:CN
State or Province Name (full name) []:Hubei
Locality Name (eg, city) [Default City]:Wuhan
Organization Name (eg, company) [Default Company Ltd]:abcdefg
Organizational Unit Name (eg, section) []:Tkcloud
Common Name (eg, your name or your server's hostname) []:10.95.197.3
Email Address []:

2、为server端生成证书

a. 生成私有秘钥

[root@ws3 certs]# openssl genrsa -out server.key 2048
Generating RSA private key,  bit long modulus
...................................................+++
............+++
e is  (0x10001)

b. 生成证书请求csr文件

[root@ws3 certs]# openssl req -new -key server.key -out server.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name ( letter code) [XX]:CN
State or Province Name (full name) []:Hubei
Locality Name (eg, city) [Default City]:Wuhan
Organization Name (eg, company) [Default Company Ltd]:abcdefg
Organizational Unit Name (eg, section) []:Cloud
Common Name (eg, your name or your server's hostname) []:10.95.197.3
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

c. 生成证书

[root@ws3 certs]# openssl ca -in server.csr -out server.crt -cert rootCA.crt -keyfile ca.key -days 3650
Using configuration from /etc/pki/tls/openssl.cnf
/etc/pki/CA/index.txt: No such file or directory
unable to open '/etc/pki/CA/index.txt'
:error::system library:fopen:No such file or directory:bss_file.c::fopen('/etc/pki/CA/index.txt','r')
:error::BIO routines:FILE_CTRL:system lib:bss_file.c::

错误分析：
缺乏/etc/pki/CA/index.txt，对应的创建一个空文件即可。

再次执行证书生成过程：

[root@ws3 certs]# openssl ca -in server.csr -out server.crt -cert rootCA.crt -keyfile ca.key -days 3650
Using configuration from /etc/pki/tls/openssl.cnf
/etc/pki/CA/serial: No such file or directory
error while loading serial number
:error::system library:fopen:No such file or directory:bss_file.c::fopen('/etc/pki/CA/serial','r')
:error::BIO routines:FILE_CTRL:system lib:bss_file.c::

错误分析：
缺乏/etc/pki/CA/serial文件，对应的创建这个文件。
再次执行上述生成指令：

[root@ws3 certs]# openssl ca -in server.csr -out server.crt -cert rootCA.crt -keyfile ca.key -days 3650
Using configuration from /etc/pki/tls/openssl.cnf
unable to load number from /etc/pki/CA/serial
error while loading serial number
:error:0D066096:asn1 encoding routines:a2i_ASN1_INTEGER:short line:f_int.c::

错误分析：
缺乏序号数据，是没有序号数据。写入1，保存后，继续执行上述过程。

[root@ws3 certs]# openssl ca -in server.csr -out server.crt -cert rootCA.crt -keyfile ca.key -days 3650
Using configuration from /etc/pki/tls/openssl.cnf
unable to load number from /etc/pki/CA/serial
error while loading serial number
:error:0D066096:asn1 encoding routines:a2i_ASN1_INTEGER:short line:f_int.c::

错误分析：
写的数据格式不对，需要写入两位的01格式，保存后继续运行。

[root@ws3 certs]# openssl ca -in server.csr -out server.crt -cert rootCA.crt -keyfile ca.key -days 3650
Using configuration from /etc/pki/tls/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number:  (0x1)
        Validity
            Not Before: Jan  ::  GMT
            Not After : Jan  ::  GMT
        Subject:
            countryName               = CN
            stateOrProvinceName       = Hubei
            organizationName          = abcdefg
            organizationalUnitName    = Cloud
            commonName                = 10.95.197.3
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                :F2:F6:::DB:1A::B7:::::A0:FE:DB:6F::A9:DE
            X509v3 Authority Key Identifier:
                keyid:DF:2F:DC:D6::2A::C0:D0::6C:::A8:::F4:9B:EB:DD

Certificate is to be certified until Jan  ::  GMT ( days)
Sign the certificate? [y/n]:y

 out of  certificate requests certified, commit? [y/n]y
Write out database with  new entries
Data Base Updated

CA这个信息为FALSE，表明这个证书不是根证书。

上面的rootCA.crt是根证书，看看内容：

[root@ws3 certs]# openssl x509 -text -in rootCA.crt -noout
Certificate:
    Data:
        Version:  (0x2)
        Serial Number:
            db::ba:::::
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=CN, ST=Hubei, L=Wuhan, O=abcdefg, OU=Tkcloud, CN=10.95.197.3
        Validity
            Not Before: Jan  ::  GMT
            Not After : Dec  ::  GMT
        Subject: C=CN, ST=Hubei, L=Wuhan, O=abcdefg, OU=Tkcloud, CN=10.95.197.3
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: ( bit)
                Modulus:
                    ::b4:::5b:c6::b4::1c:5f:::b8:
                    bf:8a:9b:e1:fa::::::2b:6e::b9::
                    a2:1c::::da:fb:5b::6b:db:bd::cd::
                    :ca::3e:2f:bb:c3:b5::4d:c9:d6:9c:1b:b9:
                    :::e8:ed:5a:d9:ca:::4e:7d:e6::8f:
                    7e:::::9c::d4:ff::c4:aa:dc:dd:de:
                    :::e2:9c:3d:::4d:d1:5a::ea:b8::
                    :1e:b8::a3:6f::ba:b2::::5c:8b:0b:
                    d3::be:a1::e6::::cf::::3a::
                    f0:e1:c8:::1e:cf:fb:4a:ee:5a:a9:7d:bc::
                    d2:fe:2c:f5:8f:a4:b2:cc:::d2:9d:a0:d2:2e:
                    4e:4f:e7::6c:0d:::::b6:7c:::f6:
                    e9:c6::5e::ea::::2d::e2:f2:bf::
                    ::7e::cf:bd:2a::::c1:8f:c5::9e:
                    :f8::::::c3::2f:b4:fc:d2:::
                    cb:0c:dd:6f:ef:9f:5d:::4e::2b::2e:3a:
                    :8e:c9::f0:7c:::a3:ac:f7::9d:::
                    e7:f9
                Exponent:  (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                AB:2E::BE::CB:A1::A4:::A8:CB::2A:3F:ED:4C:1E:
            X509v3 Authority Key Identifier:
                keyid:AB:2E::BE::CB:A1::A4:::A8:CB::2A:3F:ED:4C:1E:

            X509v3 Basic Constraints:
                CA:TRUE
    Signature Algorithm: sha256WithRSAEncryption
         4c::ad::4f:9d:e6:c3:f2:::::4f:::da:1c:
         c4:d7:::0f:1a:d6:2b:e8:8e:9d::6e:::ee:b0:c2:
         ::2e:e2:eb:2e:c0:a7::ba::dc:b6:::f9:7d:ff:
         :dc:dc::d3:aa::2a:fe:f4::c7:0e:f8:2e:de:2d::
         a0:a1:f5::f1:cc:8f:2f::fe:0c::6d:de::ff::8c:
         ::::ea:2b:b1:7d:ac:e4:b4:c0:e7:::::da:
         :::::0a:6d:3d:a5:de::9b:be::ef:d0:f4:2a:
         a0:db::6e:6c:bf:f6:fb:a7:3f:1c:4b:bd:c6:6c:9f::3b:
         d3:d3:b3:7f:ce:b8::::c1::8e::c2::d1::ee:
         ::e2::a7:0c::3a:b9:::c6::::::e7:
         ed::fc::d9:7e::f8:a3::8a:a2:::b5:e0:0e:9d:
         4d:3a:b6::::0d::ac:::0b::::::c8:
         0d:ea:ed::e9:ff:4a:3e:e5::::e2::::f1::
         :d9:6b:5b::bf::7f:ad:0d:2f::d6:fb::a4:e5::
         1c:::de

证书生成完毕后，查看上面创建的index.txt以及serial文件：

[root@ws3 certs]# vi /etc/pki/CA/index.txt
V       290114143842Z                 unknown /C=CN/ST=Hubei/O=abcdefg/OU=Cloud/CN=10.95.197.3

[root@ws3 certs]# vi /etc/pki/CA/serial

注意：起初index.txt是空的，证书创建成功后，写入了一条记录。serial文件，起初是01，然而，现在变成了02.

3. 为客户端生成证书

这里，省略生成私钥，以及证书请求的过程，重点关注基于根证书rootCA.crt生成证书的过程。

[root@ws3 certs]# openssl ca -in client.csr -out client.crt -cert rootCA.crt -keyfile ca.key
Using configuration from /etc/pki/tls/openssl.cnf
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number:  (0x2)
        Validity
            Not Before: Jan  ::  GMT
            Not After : Jan  ::  GMT
        Subject:
            countryName               = CN
            stateOrProvinceName       = Hubei
            organizationName          = abcdefg
            organizationalUnitName    = cloud
            commonName                = client
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                D7:A0:::::1F:E1:::EA::::3A:A5::7D:5B:
            X509v3 Authority Key Identifier:
                keyid:DF:2F:DC:D6::2A::C0:D0::6C:::A8:::F4:9B:EB:DD

Certificate is to be certified until Jan  ::  GMT ( days)
Sign the certificate? [y/n]:y

 out of  certificate requests certified, commit? [y/n]y
Write out database with  new entries
Data Base Updated

客户证书只有1年（不加参数-days的话，默认是1年），而服务端证书时候10年的有效期。

4. 验证双向SSL的通信过程。

1）. 配置emqtt

## 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_peer

## 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

上述几个红色的部分，是涉及SSL通信要用到的。单双向验证的核心参数是listener.ssl.external.verify = verify_peer，这里是双向验证，即服务端要向客户端发起身份验证工作。verify_none表示服务端不对客户端进行身份验证。

2）. 这里消费者客户端使用的是MQTT.fx客户端工具（1.7.1），跑在windows机器上。

a. 按照下面的config.jpg图片显示内容，配置好相关信息。

emqtt配置了用户身份认证，是通过用户名和密码做的。必须输入上述参数。

上图中配置的证书相关的参数对应的文件，就是前面生成的证书相关文件，copy到了MQTT.fx所在的windows机器上了。

b. 按照图connection.jpg点击connect即可，如图所示表示连接成功。

c. 按照图片subscribe.jpg所示，进行订阅。

3）. 消息生产者跑在Linux机器上，通过mosquitto_pub实现。

[root@ws3 certs]# mosquitto_pub -h 10.95.197.3 -t taikang/rulee --cafile /opt/certs/rootCA.crt --cert /opt/certs/client.crt --key /opt/certs/client.key -u water -P water -m "hellooooo my iot platform"

此时，MQTT.fx客户端上收到了刚才发送的数据，结果如下图.

4）. 这里，基于上面listener.ssl.external.verify = verify_peer （broker要验证client的身份）做些方向测试验证，主要验证是不是双向验证逻辑。

a. MQTT.fx上，将证书中client.key换成其他的key，和client.crt不配对的，看能否建立连接。效果如图下图. 而且，配置中根证书，客户证书，客户私钥，这三个任何一个配置不匹配，会出现不同的错误信息，自行尝试验证。

b. Mosquitto_pub端，选择将cert的参数选成另外一个证书，和上述的client.key不匹配即可，错误如下：

[root@ws3 certs]# mosquitto_pub -h 10.95.197.3 -t taikang/rulee --cafile /opt/certs/rootCA.crt --cert /etc/emqttd/certs/client-cert.pem --key /opt/certs/client.key -u water -P water -m "hellooooo5" -d
Error: Unable to load client key file "/opt/certs/client.key".
OpenSSL Error: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch
Unable to connect (A TLS error occurred.).

从上面a和b两边的测试验证，说明自行生成的客户端和服务端证书，在emqtt配置成双向验证的情况下，工作是符合设定的业务逻辑的。

下一篇博文，将从wireshark抓包的角度分析SSL通信模式下，单向验证和双向验证，在SSL/TLS消息流上的差异。