如何获取HTTP Demo文件夹下的ca.crt文件

开发者在开发过程中，可能会遇到各种各样的网络环境。尤其是需要加密的时候，就必须要涉及到证书，做到双向认证，才能保证通信可靠性。避免被伪基站嗅探数据。

HTTP Demo中，提供了和baidu直连的示例和证书，但是有的开发者不知道这个证书的来历，在此给大家讲解一下。

（linux自带openssl，如果是windows系统，请自行搜索并安装对应的exe，或者使用cygwin，mingw，WSL）

打开终端，执行如下命令：

openssl s_client -showcerts -connect www.baidu.com:443

稍候数秒，终端会打印如下数据：

[delectate@localhost ~]$ openssl s_client -showcerts -connect www.baidu.com:443
CONNECTED(00000003)
depth=2 C = US, O = "VeriSign, Inc.", OU = VeriSign Trust Network, OU = 
"(c) 2006 VeriSign, Inc. - For authorized use only", CN = VeriSign Class
 3 Public Primary Certification Authority - G5
verify return:1
depth=1 C = US, O = Symantec Corporation, OU = Symantec Trust Network, CN = Symantec Class 3 Secure Server CA - G4
verify return:1
depth=0 C = CN, ST = beijing, L = beijing, O = "BeiJing Baidu Netcom 
Science Technology Co., Ltd", OU = service operation department., CN = 
baidu.com
verify return:1
---
Certificate chain
 0 s:/C=CN/ST=beijing/L=beijing/O=BeiJing Baidu Netcom Science Technology Co., Ltd/OU=service operation department./CN=baidu.com
   i:/C=US/O=Symantec Corporation/OU=Symantec Trust Network/CN=Symantec Class 3 Secure Server CA - G4
-----BEGIN CERTIFICATE-----
MIIHOjCCBiKgAwIBAgIPAaAMWZKgoUJvdRQzvVy/MA0GCSqGSIb3DQEBCwUAMH4x
CzAJBgNVBAYTAlVTMR0wGwYDVQQKExRTeW1hbnRlYyBDb3Jwb3JhdGlvbjEfMB0G
A1UECxMWU3ltYW50ZWMgVHJ1c3QgTmV0d29yazEvMC0GA1UEAxMmU3ltYW50ZWMg
Q2xhc3MgMyBTZWN1cmUgU2VydmVyIENBIC0gRzQwHhcNMTYwODE1MDAwMDAwWhcN
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IFNjaWVuY2UgVGVjaG5vbG9neSBDby4sIEx0ZDEmMCQGA1UECwwdc2VydmljZSBv
cGVyYXRpb24gZGVwYXJ0bWVudC4xEjAQBgNVBAMMCWJhaWR1LmNvbTCCASIwDQYJ
KoZIhvcNAQEBBQADggEPADCCAQoCggEBAMsV6Ty0lfOjGN04Pmd8m0OuU0aWrFnm
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LTzo3DYr1v3qgw30B/37GzgST+iXqZtWj1FjVrawzQIhAMxUeruo6bLLmlqsE4hW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-----END CERTIFICATE-----
 1 s:/C=US/O=Symantec Corporation/OU=Symantec Trust Network/CN=Symantec Class 3 Secure Server CA - G4
   i:/C=US/O=VeriSign, Inc./OU=VeriSign Trust Network/OU=(c) 2006 
VeriSign, Inc. - For authorized use only/CN=VeriSign Class 3 Public 
Primary Certification Authority - G5
-----BEGIN CERTIFICATE-----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Fpd6UiFjdS8W+cRmvvW1Cdj/JwDNRHxvSz+w9wIDAQABo4IBYzCCAV8wEgYDVR0T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-----END CERTIFICATE-----
 2 s:/C=US/O=VeriSign, Inc./OU=VeriSign Trust Network/OU=(c) 2006 
VeriSign, Inc. - For authorized use only/CN=VeriSign Class 3 Public 
Primary Certification Authority - G5
   i:/C=US/O=VeriSign, Inc./OU=Class 3 Public Primary Certification Authority
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
---
Server certificate
subject=/C=CN/ST=beijing/L=beijing/O=BeiJing Baidu Netcom Science 
Technology Co., Ltd/OU=service operation department./CN=baidu.com
issuer=/C=US/O=Symantec Corporation/OU=Symantec Trust Network/CN=Symantec Class 3 Secure Server CA - G4
---
No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 5095 bytes and written 327 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
    Session-ID: 5CCFC38D363D2F631398127D394316164EF8817C8C8394A471FBF938117784BB
    Session-ID-ctx: 
    Master-Key: BBE5F014465E6EE86F3DE99E413B75F5EEE9D8316C108AA847D8AF270B7CC6F3AF89F400C3A4176DD79B070557A82C4E
    Key-Arg   : None
    Krb5 Principal: None
    PSK identity: None
    PSK identity hint: None
    TLS session ticket lifetime hint: 72000 (seconds)
    TLS session ticket:
    0000 - 43 2b 4c 8f c3 68 49 2d-31 65 ee d0 67 35 a7 c9   C+L..hI-1e..g5..
    0010 - b7 fa 8b 26 85 b8 fa 77-29 1a 95 66 0c 1b 16 10   ...&...w)..f....
    0020 - 0e ba d1 b4 27 6c 00 f4-c4 41 c9 34 cd ee 31 13   ....'l...A.4..1.
    0030 - 1e d8 9f de 1e 20 f4 97-09 0c 44 b1 bc 59 6a d0   ..... ....D..Yj.
    0040 - 5a 32 d6 a4 88 57 78 c9-f8 25 7e b0 64 55 45 6a   Z2...Wx..%~.dUEj
    0050 - 1d 02 b2 ed 3e c6 5c e4-4c c6 d8 b6 aa 3c 9d 77   ....>.\.L....<.w
    0060 - 01 05 10 8e 77 09 32 12-a0 b2 1d 87 60 58 fc 5b   ....w.2.....`X.[
    0070 - 79 3a 15 66 48 d6 d3 b6-ce 24 52 f8 3f a9 53 f9   y:.fH....$R.?.S.
    0080 - 76 ac e3 05 bb 7b 2a b1-32 b4 3b c1 65 4c 6f 33   v....{*.2.;.eLo3
    0090 - 23 ff 9d 25 e3 a5 69 75-e9 31 bf 2b 26 3c 4e 76   #..%..iu.1.+&    Start Time: 1497836829
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---
^C

最后不用等超时的，按下ctrl+c终止即可。

返回的数据中，—–BEGIN CERTIFICATE—-–表示证书起始，—–END CERTIFICATE—–表示证书终止。

如此一来，返回的数据就分成了3个“证书”。第一段证书“标题”是Certificate chain，不是我们需要的，舍弃掉：

第二段是

VeriSign, Inc. - For authorized use only/CN=VeriSign Class 3 Public 
Primary Certification Authority - G5

也就是我们需要的东西啦。从—–BEGIN CERTIFICATE—-–至—–END CERTIFICATE—–的所有文字，都要拷贝出来，放到ca.crt文件中：

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

好的，接下来把 ca.cr t随同 http demo 下载到模块内即可啦。

如果希望使用https，但是不希望进行证书认证，可以使用如下代码：

http.request("GET", "https://www.baidu.com/", nil, nil, nil, 30000, cbFnc)

对于MQTT，可以使用如下代码：

mqttClient:connect("lbsmqtt.airm2m.com", 1884, "tcp_ssl", {})