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-----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-----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

  1. 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

  1. 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-----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-----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.