Linux: working with SSL certificates

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If you have to enable secure connections to your service(s), you will need to buy a certificate or generate a self signed certificate for it.
If you have to buy one, you have to generate a private certificate and a certificate request.
If you will use a self signed certificate, you will need to generate a private, a request and a public certificate.

You can do that by using the 'openssl' tool. First at all, you have to generate a password, I'm usually using 'apg':
smocanu@debian7:~$ apg -n1 -m8 -x8 -t
tiWiejTo (ti-Wiej-To)
After that we are ready to generate the private certificate, this one should be kept safely, no one else should have it. I'm generating a 512bits RSA certificate:
smocanu@debian7:~$ openssl genrsa -des3 -out ss.example.com.key 512
Generating RSA private key, 512 bit long modulus
........................++++++++++++
...................++++++++++++
e is 65537 (0x10001)
Enter pass phrase for ss.example.com.key:
Verifying - Enter pass phrase for ss.example.com.key:
Next, you have to generate a certificate request for the private certificate generated before:
smocanu@debian7:~$ openssl req -new -key ss.example.com.key -out ss.example.com.csr
Generating a 2048 bit RSA private key
.........+++
...........................+++
writing new private key to 'privkey.pem'
Enter PEM pass phrase:
Verifying - Enter PEM 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]:RO
State or Province Name (full name) [Some-State]:N/A
Locality Name (eg, city) []:Bucharest
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Example
Organizational Unit Name (eg, section) []:IT
Common Name (e.g. server FQDN or YOUR name) []:*.example.com
Email Address []:it@example.com

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
And the last thing, you have to generate the public certificate, for the certificate request and private keys generated before:
smocanu@debian7:~$ openssl x509 -req -days 365 -in ss.example.com.csr -signkey ss.example.com.key -out ss.example.com.crt
Signature ok
subject=/C=RO/ST=N/A/L=Bucharest/O=Example/OU=IT/CN=*.example.com/emailAddress=it@example.com
Getting Private key
Enter pass phrase for ss.example.com.key:
If you will install this certificate on a server that is not supporting password protected certificates, you have to remove the password from the private key:
smocanu@debian7:~$ openssl rsa -in ss.example.com.key -out ss.example.com.pem
Enter pass phrase for ss.example.com.key:
writing RSA key
If  you need to check your certificates, you can do that using openssl. Usually you will need to verify the public certificate and you can do that like this:
smocanu@debian7:~$ openssl x509 -in ss.example.com.crt -text -noout
Certificate:
    Data:
        Version: 1 (0x0)
        Serial Number: 14383028987686658916 (0xc79ac8a8e535a364)
    Signature Algorithm: sha1WithRSAEncryption
        Issuer: C=RO, ST=N/A, L=Bucharest, O=Example, OU=IT, CN=*.example.com/emailAddress=it@example.com
        Validity
            Not Before: Jun  3 17:10:14 2014 GMT
            Not After : Jun  3 17:10:14 2015 GMT
        Subject: C=RO, ST=N/A, L=Bucharest, O=Example, OU=IT, CN=*.example.com/emailAddress=it@example.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (512 bit)
                Modulus:
                    00:b6:84:83:ff:1c:33:a7:61:ba:71:31:98:9d:5b:
                    93:8d:72:78:0c:5d:89:86:aa:d6:ba:dd:36:0e:58:
                    ad:03:5c:24:27:93:01:34:04:07:b8:6f:48:41:49:
                    78:9d:4c:2e:64:e2:29:48:c7:9d:7c:b5:d1:fd:9d:
                    f9:69:3f:84:c7
                Exponent: 65537 (0x10001)
    Signature Algorithm: sha1WithRSAEncryption
         3e:6b:bd:c9:0f:79:c3:ec:70:d8:8d:6b:d4:dc:96:2c:71:4a:
         d0:3d:cc:46:c1:cf:f8:af:40:a3:43:f3:66:a3:7e:c8:eb:4e:
         2c:fc:8c:1b:e2:e2:06:ba:17:f2:b3:f4:30:ba:90:37:e4:9e:
         64:53:bc:bc:13:f1:74:c6:69:92
If you have to check the certificate request, you can do that also with openssl:
smocanu@debian7:~$ openssl req -in ss.example.com.csr -text -noout
Certificate Request:
    Data:
        Version: 0 (0x0)
        Subject: C=RO, ST=N/A, L=Bucharest, O=Example, OU=IT, CN=*.example.com/emailAddress=it@example.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:a5:b0:34:79:e3:a4:8f:1e:38:29:d8:31:8a:0f:
                    71:20:e3:24:09:b1:1c:f1:b6:e4:0f:10:a8:c8:38:
                    77:de:00:96:05:29:1c:ff:41:a8:a6:1c:14:96:7d:
                    d3:6b:85:2b:27:c3:57:52:95:fa:25:d4:d3:c2:00:
                    e3:aa:3d:69:7a:e0:4f:d2:fc:91:3c:fc:0e:cd:29:
                    6d:12:bc:0a:e0:4f:be:51:25:9d:38:7a:22:fc:24:
                    59:af:4e:69:f3:4c:01:92:d3:2f:ef:5f:d8:e4:3a:
                    09:76:a6:be:87:59:97:47:27:a1:2a:6f:c7:e0:be:
                    c8:ab:d9:0e:8e:d6:24:21:70:49:95:30:10:af:69:
                    63:71:65:9a:04:29:89:cf:8e:6f:4d:1b:b8:d7:3e:
                    98:1f:c2:d2:37:69:2e:40:bc:d4:f6:52:0d:7e:e4:
                    42:69:02:b2:7a:92:bf:a6:f9:a5:12:bc:d4:ca:9d:
                    dc:b1:b2:9f:49:b9:8e:be:7b:8b:7f:61:83:d9:55:
                    ee:19:c9:ef:4a:3a:0e:7a:15:07:8e:6b:76:d0:ed:
                    29:85:5e:f0:32:b0:14:b1:e0:41:9c:f3:48:77:cf:
                    ae:0b:59:d2:71:a5:a7:24:78:3a:92:fc:9d:3b:5b:
                    ec:3a:b4:66:cf:f4:34:ab:53:03:d8:de:a1:8f:ab:
                    0c:47
                Exponent: 65537 (0x10001)
        Attributes:
            a0:00
    Signature Algorithm: sha1WithRSAEncryption
         16:a0:17:35:e5:b9:80:2d:f0:e8:2c:69:98:06:0c:63:f7:97:
         35:e5:85:9f:4f:4a:82:75:52:2a:15:86:1f:cf:3f:71:40:9c:
         4e:ba:ba:22:08:a2:d3:14:86:15:97:53:d5:47:99:e1:0c:f6:
         95:dc:b6:70:13:27:54:37:c2:fa:2e:5a:db:e8:5b:d7:7a:aa:
         55:60:42:b9:28:8c:0e:53:64:48:09:26:fd:4a:56:55:20:41:
         e1:5c:67:c6:21:1f:28:ae:16:d0:35:bf:ef:39:27:be:71:a3:
         42:88:10:7f:b7:18:e8:3d:60:fc:50:eb:dd:30:8a:db:ca:5c:
         98:04:f1:62:68:69:04:a2:a0:91:e0:a1:f1:41:7a:f3:03:12:
         58:a6:b5:65:06:d0:c7:d9:d3:ad:5e:6e:cf:21:16:cd:da:48:
         d6:f5:dd:38:a2:85:2e:15:37:5c:43:9c:15:f4:0c:79:88:4c:
         3d:c8:65:0a:10:3a:dd:0b:c8:6e:85:e9:aa:ba:b4:01:80:35:
         97:8a:2d:37:08:a9:d1:ae:98:4e:f7:36:11:7d:27:44:dd:09:
         86:57:05:f1:e8:a7:88:df:ab:9b:43:e9:91:4f:85:1f:1b:69:
         28:8d:74:c1:74:30:ef:7a:d5:07:74:69:1d:93:dc:c5:7e:28:
         6a:18:30:7e
 The private certificate can also be verified using openssl:
smocanu@debian7:~$ openssl rsa -in ss.example.com.pem -text -noout
Private-Key: (512 bit)
modulus:
    00:b6:84:83:ff:1c:33:a7:61:ba:71:31:98:9d:5b:
    93:8d:72:78:0c:5d:89:86:aa:d6:ba:dd:36:0e:58:
    ad:03:5c:24:27:93:01:34:04:07:b8:6f:48:41:49:
    78:9d:4c:2e:64:e2:29:48:c7:9d:7c:b5:d1:fd:9d:
    f9:69:3f:84:c7
publicExponent: 65537 (0x10001)
privateExponent:
    23:66:4a:4f:a5:81:a3:3a:42:36:08:1f:88:8d:a5:
    6d:ae:c0:f7:ed:00:6a:7d:22:0e:b6:2e:f0:d3:64:
    23:1d:5d:0b:dc:64:5a:62:ba:b7:11:14:bf:5d:a7:
    73:9a:87:14:a1:c0:ce:e1:4f:cf:44:06:0d:80:ca:
    45:c1:f7:99
prime1:
    00:dc:91:b0:62:6a:9d:81:37:5f:39:aa:c1:88:d8:
    b8:5f:a5:dc:b4:5a:6e:a7:ab:fb:07:44:1a:72:aa:
    b1:7a:bb
prime2:
    00:d3:d6:10:0d:47:89:2f:33:81:ee:b7:ac:64:cb:
    e3:7c:e9:fb:bd:8b:13:29:3d:ca:93:44:be:b8:f1:
    43:3b:65
exponent1:
    00:d8:79:23:e3:73:3f:a1:d1:f6:63:62:73:0f:1b:
    a3:d8:3b:b0:a0:51:20:c8:ee:c1:30:20:66:d4:a3:
    32:0c:81
exponent2:
    00:b2:73:19:82:96:48:92:62:a9:8a:17:60:3a:69:
    27:72:0b:09:ee:5a:42:01:f3:f3:ba:ab:a6:9e:d5:
    5e:f5:a1
coefficient:
    00:ce:99:04:b6:ac:a4:63:a2:c1:a9:d2:ef:bd:3e:
    96:56:00:0a:78:19:dc:4a:fe:d9:e2:4e:c2:5e:9f:
    8b:5a:79

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