108 lines
4.3 KiB
Text
108 lines
4.3 KiB
Text
<DRAFT!>
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HOWTO certificates
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1. Introduction
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How you handle certificates depend a great deal on what your role is.
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Your role can be one or several of:
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- User of some client software
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- User of some server software
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- Certificate authority
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This file is for users who wish to get a certificate of their own.
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Certificate authorities should read ca.txt.
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In all the cases shown below, the standard configuration file, as
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compiled into openssl, will be used. You may find it in /etc/,
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/usr/local/ssl/ or somewhere else. The name is openssl.cnf, and
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is better described in another HOWTO <config.txt?>. If you want to
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use a different configuration file, use the argument '-config {file}'
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with the command shown below.
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2. Relationship with keys
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Certificates are related to public key cryptography by containing a
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public key. To be useful, there must be a corresponding private key
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somewhere. With OpenSSL, public keys are easily derived from private
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keys, so before you create a certificate or a certificate request, you
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need to create a private key.
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Private keys are generated with 'openssl genrsa' if you want a RSA
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private key, or 'openssl gendsa' if you want a DSA private key.
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Further information on how to create private keys can be found in
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another HOWTO <keys.txt?>. The rest of this text assumes you have
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a private key in the file privkey.pem.
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3. Creating a certificate request
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To create a certificate, you need to start with a certificate
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request (or, as some certificate authorities like to put
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it, "certificate signing request", since that's exactly what they do,
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they sign it and give you the result back, thus making it authentic
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according to their policies). A certificate request can then be sent
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to a certificate authority to get it signed into a certificate, or if
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you have your own certificate authority, you may sign it yourself, or
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if you need a self-signed certificate (because you just want a test
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certificate or because you are setting up your own CA).
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The certificate is created like this:
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openssl req -new -key privkey.pem -out cert.csr
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Now, cert.csr can be sent to the certificate authority, if they can
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handle files in PEM format. If not, use the extra argument '-outform'
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followed by the keyword for the format to use (see another HOWTO
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<formats.txt?>). In some cases, that isn't sufficient and you will
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have to be more creative.
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When the certificate authority has then done the checks the need to
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do (and probably gotten payment from you), they will hand over your
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new certificate to you.
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Section 5 will tell you more on how to handle the certificate you
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received.
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4. Creating a self-signed certificate
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If you don't want to deal with another certificate authority, or just
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want to create a test certificate for yourself, or are setting up a
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certificate authority of your own, you may want to make the requested
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certificate a self-signed one. If you have created a certificate
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request as shown above, you can sign it using the 'openssl x509'
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command, for example like this (to create a self-signed CA
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certificate):
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openssl x509 -req -in cert.csr -extfile openssl.cnf -extensions v3_ca \
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-signkey privkey.pem -out cacert.pem -trustout
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5. What to do with the certificate
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If you created everything yourself, or if the certificate authority
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was kind enough, your certificate is a raw DER thing in PEM format.
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Your key most definitely is if you have followed the examples above.
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However, some (most?) certificate authorities will encode them with
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things like PKCS7 or PKCS12, or something else. Depending on your
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applications, this may be perfectly OK, it all depends on what they
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know how to decode. If not, There are a number of OpenSSL tools to
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convert between some (most?) formats.
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So, depending on your application, you may have to convert your
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certificate and your key to various formats, most often also putting
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them together into one file. The ways to do this is described in
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another HOWTO <formats.txt?>, I will just mention the simplest case.
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In the case of a raw DER thing in PEM format, and assuming that's all
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right for yor applications, simply concatenating the certificate and
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the key into a new file and using that one should be enough. With
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some applications, you don't even have to do that.
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By now, you have your cetificate and your private key and can start
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using the software that depend on it.
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--
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Richard Levitte
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