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      2 			HOWTO certificates
      3 
      4 1. Introduction
      5 
      6 How you handle certificates depends a great deal on what your role is.
      7 Your role can be one or several of:
      8 
      9   - User of some client application
     10   - User of some server application
     11   - Certificate authority
     12 
     13 This file is for users who wish to get a certificate of their own.
     14 Certificate authorities should read https://www.openssl.org/docs/apps/ca.html.
     15 
     16 In all the cases shown below, the standard configuration file, as
     17 compiled into openssl, will be used.  You may find it in /etc/,
     18 /usr/local/ssl/ or somewhere else.  By default the file is named
     19 openssl.cnf and is described at https://www.openssl.org/docs/apps/config.html.
     20 You can specify a different configuration file using the
     21 '-config {file}' argument with the commands shown below.
     22 
     23 
     24 2. Relationship with keys
     25 
     26 Certificates are related to public key cryptography by containing a
     27 public key.  To be useful, there must be a corresponding private key
     28 somewhere.  With OpenSSL, public keys are easily derived from private
     29 keys, so before you create a certificate or a certificate request, you
     30 need to create a private key.
     31 
     32 Private keys are generated with 'openssl genrsa -out privkey.pem' if
     33 you want a RSA private key, or if you want a DSA private key:
     34 'openssl dsaparam -out dsaparam.pem 2048; openssl gendsa -out privkey.pem dsaparam.pem'.
     35 
     36 The private keys created by these commands are not passphrase protected;
     37 it might or might not be the desirable thing.  Further information on how to
     38 create private keys can be found at https://www.openssl.org/docs/HOWTO/keys.txt.
     39 The rest of this text assumes you have a private key in the file privkey.pem.
     40 
     41 
     42 3. Creating a certificate request
     43 
     44 To create a certificate, you need to start with a certificate request
     45 (or, as some certificate authorities like to put it, "certificate
     46 signing request", since that's exactly what they do, they sign it and
     47 give you the result back, thus making it authentic according to their
     48 policies).  A certificate request is sent to a certificate authority
     49 to get it signed into a certificate. You can also sign the certificate
     50 yourself if you have your own certificate authority or create a
     51 self-signed certificate (typically for testing purpose).
     52 
     53 The certificate request is created like this:
     54 
     55   openssl req -new -key privkey.pem -out cert.csr
     56 
     57 Now, cert.csr can be sent to the certificate authority, if they can
     58 handle files in PEM format.  If not, use the extra argument '-outform'
     59 followed by the keyword for the format to use (see another HOWTO
     60 <formats.txt?>).  In some cases, -outform does not let you output the
     61 certificate request in the right format and you will have to use one
     62 of the various other commands that are exposed by openssl (or get
     63 creative and use a combination of tools).
     64 
     65 The certificate authority performs various checks (according to their
     66 policies) and usually waits for payment from you. Once that is
     67 complete, they send you your new certificate.
     68 
     69 Section 5 will tell you more on how to handle the certificate you
     70 received.
     71 
     72 
     73 4. Creating a self-signed test certificate
     74 
     75 You can create a self-signed certificate if you don't want to deal
     76 with a certificate authority, or if you just want to create a test
     77 certificate for yourself.  This is similar to creating a certificate
     78 request, but creates a certificate instead of a certificate request.
     79 This is NOT the recommended way to create a CA certificate, see
     80 https://www.openssl.org/docs/apps/ca.html.
     81 
     82   openssl req -new -x509 -key privkey.pem -out cacert.pem -days 1095
     83 
     84 
     85 5. What to do with the certificate
     86 
     87 If you created everything yourself, or if the certificate authority
     88 was kind enough, your certificate is a raw DER thing in PEM format.
     89 Your key most definitely is if you have followed the examples above.
     90 However, some (most?) certificate authorities will encode them with
     91 things like PKCS7 or PKCS12, or something else.  Depending on your
     92 applications, this may be perfectly OK, it all depends on what they
     93 know how to decode.  If not, there are a number of OpenSSL tools to
     94 convert between some (most?) formats.
     95 
     96 So, depending on your application, you may have to convert your
     97 certificate and your key to various formats, most often also putting
     98 them together into one file.  The ways to do this is described in
     99 another HOWTO <formats.txt?>, I will just mention the simplest case.
    100 In the case of a raw DER thing in PEM format, and assuming that's all
    101 right for your applications, simply concatenating the certificate and
    102 the key into a new file and using that one should be enough.  With
    103 some applications, you don't even have to do that.
    104 
    105 
    106 By now, you have your certificate and your private key and can start
    107 using applications that depend on it.
    108 
    109 --
    110 Richard Levitte
    111