基于 OpenSSL 的 CA 创建及证书签发

http://rhythm-zju.blog.163.com/blog/static/310042008015115718637/

创建 CA

创建 CA 目录结构

按照 OpenSSL 的默认配置创建 CA ，须要在文件系统中创建相应的目录结构。相关的配置内容通常位于 /usr/ssl/openssl.cnf 内，详情可参见 config (1) 。在终端中使用以下命令创建目录结构：

$ mkdir -p ./demoCA/{private,newcerts}
$ touch ./demoCA/index.txt
$ echo 01 > ./demoCA/serial

产生的目录结构以下：

.
`-- demoCA/
    |-- index.txt
    |-- newcerts/
    |-- private/
    `-- serial

生成 CA 证书的 RSA 密钥对

首先，咱们要为 CA 创建 RSA 密钥对。打开终端，使用以下命令生成 RSA 密钥对：

$ openssl genrsa -des3 -out ./demoCA/private/cakey.pem 2048

参数解释

genrsa

用于生成 RSA 密钥对的 OpenSSL 命令。

-des3

使用 3-DES 对称加密算法加密密钥对，该参数须要用户在密钥生成过程当中输入一个口令用于加密。从此使用该密钥对时，须要输入相应的口令。若是不加该选项，则不对密钥进行加密。

-out ./demoCA/private/cakey.pem

令生成的密钥对保存到文件 ./demoCA/private/cakey.pem 。

2048

RSA 模数位数，在必定程度上表征了密钥强度。

该命令输出以下，用户应输入本身的密钥口令并确认：

Generating RSA private key, 2048 bit long modulus
................................................+++
.........................+++
e is 65537 (0x10001)
Enter pass phrase for ./demoCA/private/cakey.pem:<enter your pass-phrase>
Verifying - Enter pass phrase for ./demoCA/private/cakey.pem:<re-enter your pass-phrase>

生成 CA 证书请求

为了获取一个 CA 根证书，咱们须要先制做一份证书请求。先前生成的 CA 密钥对被用于对证书请求签名。

$ openssl req -new -days 365 -key ./demoCA/private/cakey.pem -out careq.pem

参数解释

req

用于生成证书请求的 OpenSSL 命令。

-new

生成一个新的证书请求。该参数将令 OpenSSL 在证书请求生成过程当中要求用户填写一些相应的字段。

-days 365

从生成之时算起，证书时效为 365 天。

-key ./demoCA/private/cakey.pem

指定 ./demoCA/private/cakey.pem 为证书所使用的密钥对文件。

-out careq.pem

令生成的证书请求保存到文件 careq.pem 。

该命令将提示用户输入密钥口令并填写证书相关信息字段，输出以下：

Enter pass phrase for ./demoCA/private/cakey.pem:<enter you pass-phrase>
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 (2 letter code) [AU]:CN
State or Province Name (full name) [Some-State]:ZJ
Locality Name (eg, city) []:HZ
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Some Ltd. Corp.
Organizational Unit Name (eg, section) []:Some Unit
Common Name (eg, YOUR name) []:Someone
Email Address []:some@email.com
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

对 CA 证书请求进行签名

在实际应用中，用户能够经过向知名 CA 递交证书请求来申请证书。可是在这里，咱们须要创建的是一个根 CA ，只能由咱们本身来对证书请求进行签名。因此咱们让 OpenSSL 使用证书请求中附带的密钥对对该请求进行签名，也就是所谓的“ self sign ”：

$ openssl ca -selfsign -in careq.pem -out cacert.pem

参数解释

ca

用于执行 CA 相关操做的 OpenSSL 命令。

-selfsign

使用对证书请求进行签名的密钥对来签发证书。

-in careq.pem

指定 careq.pem 为证书请求文件。

-out ./demoCA/cacert.pem

指定 ./demoCA/cacert.pem 为输出的证书。

该命令要求用户输入密钥口令并输出相关证书信息，请求用户确认：

Using configuration from /usr/lib/ssl/openssl.cnf
Enter pass phrase for ./demoCA/private/cakey.pem:<enter your pass-phrase>
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 2 (0x2)
        Validity
            Not Before: Jan 16 13:05:09 2008 GMT
            Not After : Jan 15 13:05:09 2009 GMT
        Subject:
            countryName = CN
            stateOrProvinceName = ZJ
            organizationName = Some Ltd. Corp.
            organizationalUnitName = Some Unit
            commonName = Someone
            emailAddress = some@email.com
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                75:F5:3C:CC:C1:5E:6D:C3:8B:46:A8:08:E6:EA:29:E8:22:7E:70:03
            X509v3 Authority Key Identifier:
                keyid:75:F5:3C:CC:C1:5E:6D:C3:8B:46:A8:08:E6:EA:29:E8:22:7E:70:03
Certificate is to be certified until Jan 15 13:05:09 2009 GMT (365 days)
Sign the certificate? [y/n]:y
1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

一步完成 CA 证书请求生成及签名

以上两个步骤能够合二为一。利用 ca 命令的 -x509 参数，经过如下命令同时完成证书请求生成和签名从而生成 CA 根证书：

$ openssl req -new -x509 -days 365 -key ./demoCA/private/cakey.pem -out ./demoCA/cacert.pem

参数解释

req

用于生成证书请求的 OpenSSL 命令。

-new

生成一个新的证书请求。该参数将令 OpenSSL 在证书请求生成过程当中要求用户填写一些相应的字段。

-x509

生成一份 X.509 证书。

-days 365

从生成之时算起，证书时效为 365 天。

-key ./demoCA/private/cakey.pem

指定 cakey.pem 为证书所使用的密钥对文件。

-out ./demoCA/cacert.pem

令生成的证书保存到文件 ./demoCA/cacert.pem 。

该命令输出以下，用户应输入相应的字段：

Enter pass phrase for ./demoCA/private/cakey.pem:
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 (2 letter code) [AU]:CN
State or Province Name (full name) [Some-State]:ZJ
Locality Name (eg, city) []:HZ
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Some Ltd. Corp.
Organizational Unit Name (eg, section) []:Some Unit
Common Name (eg, YOUR name) []:Someone
Email Address []:some@email.com

至此，咱们便已成功创建了一个私有根 CA 。在这个过程当中，咱们得到了一份 CA 密钥对文件./demoCA/private/cakey.pem 以及一份由此密钥对签名的 CA 根证书文件./demoCA/cacert.pem ，获得的 CA 目录结构以下：

.
|-- careq.pem
`-- demoCA/
    |-- cacert.pem
    |-- index.txt
    |-- index.txt.attr
    |-- index.txt.old
    |-- newcerts/
    |   `-- 01.pem
    |-- private/
    |   `-- cakey.pem
    |-- serial
    `-- serial.old

注：若是在 CA 创建过程当中跳过证书请求生成的步骤，则不会产生 careq.pem 文件。

签发证书

下面咱们就能够利用创建起来的 CA 进行证书签发了。

生成用户证书 RSA 密钥对

参照 CA 的 RSA 密钥对生成过程，使用以下命令生成新的密钥对：

$ openssl genrsa -des3 -out userkey.pem
Generating RSA private key, 512 bit long modulus
....++++++++++++
...++++++++++++
e is 65537 (0x10001)
Enter pass phrase for userkey.pem:<enter your pass-phrase>
Verifying - Enter pass phrase for userkey.pem:<re-enter your pass-phrase>

生成用户证书请求

参照 CA 的证书请求生成过程，使用以下命令生成新的证书请求：

$ openssl req -new -days 365 -key userkey.pem -out userreq.pem
Enter pass phrase for userkey.pem:<enter your pass-phrase>
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 (2 letter code) [AU]:CN
State or Province Name (full name) [Some-State]:ZJ
Locality Name (eg, city) []:HZ
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Some Ltd. Corp.
Organizational Unit Name (eg, section) []:Some Other Unit
Common Name (eg, YOUR name) []:Another
Email Address []:another@email.com
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

签发用户证书

如今，咱们能够用先前创建的 CA 来对用户的证书请求进行签名来为用户签发证书了。使用以下命令：

$ openssl ca -in userreq.pem -out usercert.pem

参数解释

ca

用于执行 CA 相关操做的 OpenSSL 命令。

-in userreq.pem

指定用户证书请求文件为 userreq.pem 。

-out usercert.pem

指定输出的用户证书文件为 usercert.pem 。

该命令要求用户输入密钥口令并输出相关证书信息，请求用户确认：

Using configuration from /usr/lib/ssl/openssl.cnf
Enter pass phrase for ./demoCA/private/cakey.pem:<enter your pass-phrase>
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 2 (0x2)
        Validity
            Not Before: Jan 16 14:50:22 2008 GMT
            Not After : Jan 15 14:50:22 2009 GMT
        Subject:
            countryName               = CN
            stateOrProvinceName       = ZJ
            organizationName          = Some Ltd. Corp.
            organizationalUnitName    = Some Other Unit
            commonName                = Another
            emailAddress              = another@email.com
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                97:E7:8E:84:B1:45:27:83:94:A0:DC:24:79:7B:83:97:99:0B:36:A9
            X509v3 Authority Key Identifier:
                keyid:D9:87:12:94:B2:20:C7:22:AB:D4:D5:DF:33:DB:84:F3:B0:4A:EC:A2
Certificate is to be certified until Jan 15 14:50:22 2009 GMT (365 days)
Sign the certificate? [y/n]:y
1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

至此，咱们便完成了 CA 的创建及用户证书签发的所有工做。不妨把全部 shell 命令放到一块儿纵览一下：

# 创建 CA 目录结构
mkdir -p ./demoCA/{private,newcerts}
touch ./demoCA/index.txt
echo 01 > ./demoCA/serial
# 生成 CA 的 RSA 密钥对
openssl genrsa -des3 -out ./demoCA/private/cakey.pem 2048
# 生成 CA 证书请求
openssl req -new -days 365 -key ./demoCA/private/cakey.pem -out careq.pem
# 自签发 CA 证书
openssl ca -selfsign -in careq.pem -out ./demoCA/cacert.pem
# 以上两步能够合二为一
openssl req -new -x509 -days 365 -key ./demoCA/private/cakey.pem -out ./demoCA/cacert.pem
# 生成用户的 RSA 密钥对
openssl genrsa -des3 -out userkey.pem
# 生成用户证书请求
openssl req -new -days 365 -key userkey.pem -out userreq.pem
# 使用 CA 签发用户证书
openssl ca -in userreq.pem -out usercert.pem

了解了这些基础步骤以后，就能够经过脚本甚至 makefile 的方式来将这些工做自动化。 CA.pl 和CA.sh 即是对 OpenSSL 的 CA 相关功能的简单封装，在 Debian 系统中，安装了 OpenSSL 后，能够在 /usr/lib/ssl/misc/ 目录下找到这两个文件。而 makefile 的解决方案则能够参考这里。

参考文献

• The Open–source PKI Book: A guide to PKIs and Open–source Implementations, Initialisation of the Certification Authority
  http://ospkibook.sourceforge.net/docs/OSPKI-2.4.7/OSPKI-html/initialisation.htm
• OpenSSL: Documents, OpenSSL(1)
  http://www.openssl.org/docs/apps/openssl.html
• OpenSSL Certificate Authority Setup
  http://sial.org/howto/openssl/ca/