# HOWTO: Creating your own CA with OpenSSL

author:

  Pheng Siong Ng <ngps@post1.com>

copyright:

  © 2000, 2001 by Ng Pheng Siong.

## Introduction

This is a HOWTO on creating your own certification authority (CA) with OpenSSL.

I last created a CA about a year ago, when I began work on M2Crypto and needed certificates for the SSL bits. I accepted the tools’ default settings then, e.g., certificate validity of 365 days; this meant that my certificates, including my CA’s certificate, have now expired.

Since I am using these certificates for M2Crypto’s demonstration programs (and I have forgotten the passphrase to the CA’s private key), I decided to discard the old CA and start afresh. I also decided to document the process, hence this HOWTO.

## The Procedure

I use `CA.pl`, a Perl program written by Steve Hanson and bundled with OpenSSL.

The following are the steps to create a CA:

1. Choose a directory to do your CA work. All commands are executed within this directory. Let’s call the directory `demo`.

2. Copy `CA.pl` and `openssl.cnf` into `demo`.

3. Apply the following patch to `CA.pl`, which allows it to generate a CA certificate with a validity period of 1095 days, i.e., 3 years:

       --- CA.pl.org   Sat Mar 31 12:40:13 2001
       +++ CA.pl       Sat Mar 31 12:41:15 2001
       @@ -97,7 +97,7 @@
                       } else {
                           print "Making CA certificate ...\n";
                           system ("$REQ -new -x509 -keyout " .
       -                       "${CATOP}/private/$CAKEY -out ${CATOP}/$CACERT $DAYS");
       +                       "${CATOP}/private/$CAKEY -out ${CATOP}/$CACERT -days 1095");
                           $RET=$?;
                       }
                   }

4. Create a new CA like this:

       ./CA.pl -newca

       A certificate filename (or enter to create) <enter>

       Making CA certificate ...
       Using configuration from openssl.cnf
       Generating a 1024 bit RSA private key
       ............++++++
       ......................++++++
       writing new private key to './demoCA/private/cakey.pem'
       Enter PEM pass phrase: <secret passphrase here>
       Verifying password - Enter PEM pass phrase: <secret passphrase again>
       -----
       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]:SG
       State or Province Name (full name) [Some-State]:.
       Locality Name (eg, city) []:..
       Organization Name (eg, company) [Internet Widgits Pty Ltd]:DemoCA
       Organizational Unit Name (eg, section) []:.
       Common Name (eg, YOUR name) []:DemoCA Certificate Master
       Email Address []:certmaster@democa.dom

   This creates a new CA in the directory `demoCA`. The CA’s self-signed certificate is in `demoCA/cacert.pem` and its RSA key pair is in `demoCA/private/cakey.pem`.

   `demoCA/private/cakey.pem` looks like this:

       cat demoCA/private/cakey.pem

       -----BEGIN RSA PRIVATE KEY-----
       Proc-Type: 4,ENCRYPTED
       DEK-Info: DES-EDE3-CBC,19973A9DBBB601BA

       eOq9WFScNiI4/UWEUaSnGTKpJv2JYuMD3HwQox2Q3Cd4zGqVjJ6gF3exa5126cKf
       X/bMVnwbPpuFZPiAIvaLyCjT6pYeXTBbSzs7/GQnvEOv+nYnDUFWi0Qm92qLk0uy
       pFi/M1aWheN3vir2ZlAw+DW0bOOZhj8tC7Co7lMYb0YE271b6/YRPZCwQ3GXAHUJ
       +aMYxlUDrK45aCUa/1CZDzTgk7h9cDgx2QJSIvYMYytCfI3zsuZMJS8/4OXLL0bI
       lKmAc1dwB3DqGJt5XK4WJesiNfdxeCNEgAcYtEAgYZTPIApU+kTgTCIxJl2nMW7j
       ax+Q1z7g+4MpgG20WD633D4z4dTlDdz+dnLi0rvuvxiwt+dUhrqiML1tyi+Z6EBH
       jU4/cLBWev3rYfrlp4x8J9mDte0YKOk3t0wQOHqRetTsIfdtjnFp/Hu3qDmTCWjD
       z/g7PPoO/bg/B877J9WBPbL/1hXXFYo88M+2aGlPOgDcFdiOqbLb2DCscohMbbVr
       A4mgiy2kwWfIE73qiyV7yyG8FlRvr1iib+jbT3LTGf743utYAAs7HNGuOUObhoyt
       jYvBD7ACn35P5YX7KTqvqErwdijxYCaNBCnvmRtmYSaNw9Kv1UJTxc5Vx7YLwIPk
       E9KyBgKI7vPOjWBZ27+zOvNycmv1ciNtpALAw4bWtXnhCDVTHaVDy34OkheMzNCg
       2cjcBFzOkMIjcI03KbTQXOFIQGlsTWXGzkNf/zBQ+KksT1MCj+zBXSCvlDASMckg
       kef21pGgUqPF14gKGfWX3sV4bjc1vbrRwq6zlG3nMuYqR5MtJJY9eQ==
       -----END RSA PRIVATE KEY-----

5. Next, generate a certificate request:

       ./CA.pl -newreq

       Using configuration from openssl.cnf
       Generating a 1024 bit RSA private key
       ..........++++++
       ..............++++++
       writing new private key to 'newreq.pem'
       Enter PEM pass phrase: <another secret passphrase here>
       Verifying password - Enter PEM pass phrase: <another secret passphrase again>
       -----
       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]:SG
       State or Province Name (full name) [Some-State]:..
       Locality Name (eg, city) []:.
       Organization Name (eg, company) [Internet Widgits Pty Ltd]:M2Crypto
       Organizational Unit Name (eg, section) []:.
       Common Name (eg, YOUR name) []:localhost
       Email Address []:admin@server.example.dom

       Please enter the following 'extra' attributes
       to be sent with your certificate request
       A challenge password []:<enter>
       An optional company name []:<enter>
       Request (and private key) is in newreq.pem

> The certificate request and private key in `newreq.pem` looks like this:

>     cat newreq.pem

>     -----BEGIN RSA PRIVATE KEY-----
>     Proc-Type: 4,ENCRYPTED
>     DEK-Info: DES-EDE3-CBC,41B2874DF3D02DD4

>     mg611EoVkLEooSTv+qTM0Ddmm/M1jE/Jy5RD/sc3LSMhuGu9xc26OgsTJmkQuIAh
>     J/B4lAw8G59VTG6DykeEtrG0rUBx4bggc7PKbFuiN423YjJODWcHvVgnPOzXMQt+
>     lY4tPl5+217MRHyx2NsWGrpkQNdu3GeSPOVMl3jeQiaXupONbwQ7rj42+X/VtAJP
>     W4D1NNwu8aGCPyShsEXHc/fI1WDpphYWke97pOjIZVQESFZOPty5HjIYZux4U+td
>     W81xODtq2ecJXc8fn2Wpa9y5VD1LT7oJksOuL1+Z04OVaeUe4x0swM17HlBm2kVt
>     fe/C/L6kN27MwZhE331VjtTjSGl4/gknqQDbLOtqT06f3OISsDJETm2itllyhgzv
>     C6Fi3N03rGFmKectijC+tws5k+P+HRG6sai33usk8xPokJqA+HYSWPz1XVlpRmv4
>     kdjQOdST7ovU62mOTgf3ARcduPPwuzTfxOlYONe5NioO1APVHBrInQwcpLkpOTQR
>     vI4roIN+b75/nihUWGUJn/nbbBa2Yl0N5Gs1Tyiy9Z+CcRT2TfWKBBFlEUIFl7Mb
>     J9fTV3DI+k+akbR4il1NkQ8EcSmCr3WpA0I9n0EHI7ZVpVaHxc0sqaPFl8YGdFHq
>     1Qk53C/w6+qPpDzT3yKFmG2LZytAAM1czvb6RbNRJJP2ZrpBwn/h99sUTo/yPfxY
>     nueYmFJDm0uVNtG0icXGNUfSfnjKNTtHPAgyKGetRIC3kgJz/bo2w7EI6iEjBAzK
>     l5TRm4x6ZJxwuXXMiJCehMMd8TC8ybwWO4AO19B3ebFFeTVsUgxSGA==
>     -----END RSA PRIVATE KEY-----
>     -----BEGIN CERTIFICATE REQUEST-----
>     MIIBnTCCAQYCAQAwXTELMAkGA1UEBhMCU0cxETAPBgNVBAoTCE0yQ3J5cHRvMRIw
>     EAYDVQQDEwlsb2NhbGhvc3QxJzAlBgkqhkiG9w0BCQEWGGFkbWluQHNlcnZlci5l
>     eGFtcGxlLmRvbTCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAr1nYY1Qrll1r
>     uB/FqlCRrr5nvupdIN+3wF7q915tvEQoc74bnu6b8IbbGRMhzdzmvQ4SzFfVEAuM
>     MuTHeybPq5th7YDrTNizKKxOBnqE2KYuX9X22A1Kh49soJJFg6kPb9MUgiZBiMlv
>     tb7K3CHfgw5WagWnLl8Lb+ccvKZZl+8CAwEAAaAAMA0GCSqGSIb3DQEBBAUAA4GB
>     AHpoRp5YS55CZpy+wdigQEwjL/wSluvo+WjtpvP0YoBMJu4VMKeZi405R7o8oEwi
>     PdlrrliKNknFmHKIaCKTLRcU59ScA6ADEIWUzqmUzP5Cs6jrSRo3NKfg1bd09D1K
>     9rsQkRc9Urv9mRBIsredGnYECNeRaK5R1yzpOowninXC
>     -----END CERTIFICATE REQUEST-----

> Decoding the certificate request gives the following:

>     openssl req -text -noout < newreq.pem

>     Using configuration from /usr/local/pkg/openssl/openssl.cnf
>     Certificate Request:
>        Data:
>            Version: 0 (0x0)
>            Subject: C=SG, O=M2Crypto, CN=localhost/Email=admin@server.example.dom
>            Subject Public Key Info:
>                Public Key Algorithm: rsaEncryption
>                RSA Public Key: (1024 bit)
>                    Modulus (1024 bit):
>                        00:af:59:d8:63:54:2b:96:5d:6b:b8:1f:c5:aa:50:
>                        91:ae:be:67:be:ea:5d:20:df:b7:c0:5e:ea:f7:5e:
>                        6d:bc:44:28:73:be:1b:9e:ee:9b:f0:86:db:19:13:
>                        21:cd:dc:e6:bd:0e:12:cc:57:d5:10:0b:8c:32:e4:
>                        c7:7b:26:cf:ab:9b:61:ed:80:eb:4c:d8:b3:28:ac:
>                        4e:06:7a:84:d8:a6:2e:5f:d5:f6:d8:0d:4a:87:8f:
>                        6c:a0:92:45:83:a9:0f:6f:d3:14:82:26:41:88:c9:
>                        6f:b5:be:ca:dc:21:df:83:0e:56:6a:05:a7:2e:5f:
>                        0b:6f:e7:1c:bc:a6:59:97:ef
>                    Exponent: 65537 (0x10001)
>            Attributes:
>                a0:00
>        Signature Algorithm: md5WithRSAEncryption
>            7a:68:46:9e:58:4b:9e:42:66:9c:be:c1:d8:a0:40:4c:23:2f:
>            fc:12:96:eb:e8:f9:68:ed:a6:f3:f4:62:80:4c:26:ee:15:30:
>            a7:99:8b:8d:39:47:ba:3c:a0:4c:22:3d:d9:6b:ae:58:8a:36:
>            49:c5:98:72:88:68:22:93:2d:17:14:e7:d4:9c:03:a0:03:10:
>            85:94:ce:a9:94:cc:fe:42:b3:a8:eb:49:1a:37:34:a7:e0:d5:
>            b7:74:f4:3d:4a:f6:bb:10:91:17:3d:52:bb:fd:99:10:48:b2:
>            b7:9d:1a:76:04:08:d7:91:68:ae:51:d7:2c:e9:3a:8c:27:8a:
>            75:c2

6. Now, sign the certificate request:

       ./CA.pl -sign

       Using configuration from openssl.cnf
       Enter PEM pass phrase: <CA's passphrase>
       Check that the request matches the signature
       Signature ok
       The Subjects Distinguished Name is as follows
       countryName           :PRINTABLE:'SG'
       organizationName      :PRINTABLE:'M2Crypto'
       commonName            :PRINTABLE:'localhost'
       emailAddress          :IA5STRING:'admin@server.example.dom'
       Certificate is to be certified until Mar 31 02:57:30 2002 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
       Signed certificate is in newcert.pem

> `newcert.pem` looks like this:

>     cat newcert.pem

>     Certificate:
>     Data:
>        Version: 3 (0x2)
>        Serial Number: 1 (0x1)
>        Signature Algorithm: md5WithRSAEncryption
>        Issuer: C=SG, O=DemoCA, CN=DemoCA Certificate Master/Email=certmaster@democa.dom
>        Validity
>            Not Before: Mar 31 02:57:30 2001 GMT
>            Not After : Mar 31 02:57:30 2002 GMT
>        Subject: C=SG, O=M2Crypto, CN=localhost/Email=admin@server.example.dom
>        Subject Public Key Info:
>            Public Key Algorithm: rsaEncryption
>            RSA Public Key: (1024 bit)
>                Modulus (1024 bit):
>                    00:af:59:d8:63:54:2b:96:5d:6b:b8:1f:c5:aa:50:
>                    91:ae:be:67:be:ea:5d:20:df:b7:c0:5e:ea:f7:5e:
>                    6d:bc:44:28:73:be:1b:9e:ee:9b:f0:86:db:19:13:
>                    21:cd:dc:e6:bd:0e:12:cc:57:d5:10:0b:8c:32:e4:
>                    c7:7b:26:cf:ab:9b:61:ed:80:eb:4c:d8:b3:28:ac:
>                    4e:06:7a:84:d8:a6:2e:5f:d5:f6:d8:0d:4a:87:8f:
>                    6c:a0:92:45:83:a9:0f:6f:d3:14:82:26:41:88:c9:
>                    6f:b5:be:ca:dc:21:df:83:0e:56:6a:05:a7:2e:5f:
>                    0b:6f:e7:1c:bc:a6:59:97:ef
>                Exponent: 65537 (0x10001)
>        X509v3 extensions:
>            X509v3 Basic Constraints:
>     Certificate:
>     Data:
>        Version: 3 (0x2)
>        Serial Number: 1 (0x1)
>        Signature Algorithm: md5WithRSAEncryption
>        Issuer: C=SG, O=DemoCA, CN=DemoCA Certificate Master/Email=certmaster@democa.dom
>        Validity
>            Not Before: Mar 31 02:57:30 2001 GMT
>            Not After : Mar 31 02:57:30 2002 GMT
>        Subject: C=SG, O=M2Crypto, CN=localhost/Email=admin@server.example.dom
>        Subject Public Key Info:
>            Public Key Algorithm: rsaEncryption
>            RSA Public Key: (1024 bit)
>                Modulus (1024 bit):
>                    00:af:59:d8:63:54:2b:96:5d:6b:b8:1f:c5:aa:50:
>                    91:ae:be:67:be:ea:5d:20:df:b7:c0:5e:ea:f7:5e:
>                    6d:bc:44:28:73:be:1b:9e:ee:9b:f0:86:db:19:13:
>                    21:cd:dc:e6:bd:0e:12:cc:57:d5:10:0b:8c:32:e4:
>                    c7:7b:26:cf:ab:9b:61:ed:80:eb:4c:d8:b3:28:ac:
>                    4e:06:7a:84:d8:a6:2e:5f:d5:f6:d8:0d:4a:87:8f:
>                    6c:a0:92:45:83:a9:0f:6f:d3:14:82:26:41:88:c9:
>                    6f:b5:be:ca:dc:21:df:83:0e:56:6a:05:a7:2e:5f:
>                    0b:6f:e7:1c:bc:a6:59:97:ef
>                Exponent: 65537 (0x10001)
>        X509v3 extensions:
>            X509v3 Basic Constraints:
>                CA:FALSE
>            Netscape Comment:
>                OpenSSL Generated Certificate
>            X509v3 Subject Key Identifier:
>                B3:D6:89:88:2F:B1:15:40:EC:0A:C0:30:35:3A:B7:DA:72:73:1B:4D
>            X509v3 Authority Key Identifier:
>                keyid:F9:6A:A6:34:97:6B:BC:BB:5A:17:0D:19:FC:62:21:0B:00:B5:0E:29
>                DirName:/C=SG/O=DemoCA/CN=DemoCA Certificate Master/Email=certmaster@democa.dom
>                serial:00

>     Signature Algorithm: md5WithRSAEncryption

7. In certain situations, e.g., where your certificate and private key are to be used in an unattended SSL server, you may wish to not encrypt the private key, i.e., leave the key in the clear. This decision should be governed by your site’s security policy and threat model, of course:

       openssl rsa < newkey.pem > newkey2.pem

       read RSA key
       Enter PEM pass phrase:<secret passphrase here>
       writing RSA key

   `newkey2.pem` looks like this:

       cat newkey2.pem

       -----BEGIN RSA PRIVATE KEY-----
       MIICXgIBAAKBgQCvWdhjVCuWXWu4H8WqUJGuvme+6l0g37fAXur3Xm28RChzvhue
       7pvwhtsZEyHN3Oa9DhLMV9UQC4wy5Md7Js+rm2HtgOtM2LMorE4GeoTYpi5f1fbY
       DUqHj2ygkkWDqQ9v0xSCJkGIyW+1vsrcId+DDlZqBacuXwtv5xy8plmX7wIDAQAB
       AoGAbAkU8w3W1Qu15Hle1bJSL7GMReoreqeblOBmMAZz4by0l6sXZXJpjWXo86f/
       +dASMYTMPC4ZTYtv06N07AFbjL+kDfqDMTfzQkYMHp1LAq1Ihbq1rHWSBH5n3ekq
       KiY8JKpv8DR5Po1iKaXJFuDByGDENJwYbSRSpSK3P+vkWWECQQDkEUE/ZPqqqZkQ
       2iWRPAsCbEID8SAraQl3DdCLYs/GgARfmmj4yUHEwkys9Jo1H8k4BdxugmaUwNi5
       YQ/CVzrXAkEAxNO80ArbGxPUmr11GHG/bGBYj1DUBkHZSc7dgxZdtUCLGNxQnNsg
       Iwq3n6j1sUzS3UW6abQ8bivYNOUcMKJAqQJBANQxFaLU4b/NQaODQ3aoBZpAfP9L
       5eFdvbet+7zjt2r5CpikgkwOfAmDuXEltx/8LevY0CllW+nErx9zJgVrwUsCQQCu
       76H5JiznPBDSF2FjgHWqVVdgyW4owY3mU739LHvNBLicN/RN9VPy0Suy8/CqzKT9
       lWPBXzf2k3FuUdNkRlFBAkEAmpXoybuiFR2S5Bma/ax96lVs0/VihhfC1zZP/X/F
       Br77+h9dIul+2DnyOl50zu0Sdzst1/7ay4JSDHyiBCMGSQ==
       -----END RSA PRIVATE KEY-----

That’s it! The certificate, `newcert.pem`, and the private key - `newkey.pem` (encrypted) or `newkey2.pem` (unencrypted) - are now ready to be used. You may wish to rename the files to more intuitive names.

You should also keep the CA’s certificate `demo/cacert.pem` handy for use when developing and deploying SSL or S/MIME applications.

## Conclusion

We’ve walked through the basic steps in the creation of a CA and certificates using the tools that come with OpenSSL. We did not cover more advanced topics such as constraining a certificate to be SSL-only or S/MIME-only.

There exist several HOWTOs similar to this one on the net. This one is written specifically to facilitate discussions in my other HOWTOs on developing SSL and S/MIME applications in Python using M2Crypto.