142 lines
7.3 KiB
Markdown
142 lines
7.3 KiB
Markdown
ca-scripts
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==========
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A set of **bash**(1) scripts for working with SSL Certificate Authorities.
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These scripts are designed to provide a configurable wrapping layer around
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[**openssl**(1)](http://www.openssl.org/), similar to CA.pl. They're potentially
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a little heavyweight if you just need a single self-signed certificate to secure
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an HTTPs webserver, but they may come in handy if you want to:
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* Generate multiple service certificates signed by a single authority
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* Provide signed client certificates to end users for authentication purposes
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* Provide client certificates for S/MIME encrypted e-mail or code signing
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* Easily set extensions such as x509v3 subjectAltName in your certificates
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Portability
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-----------
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Currently, these scripts are limited to systems with a recent install of
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**openssl**(1), GNU **date**(1) -- sorry BSD folks; patches welcome -- and
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version 3 or greater of **bash**(1).
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Installation
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------------
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There aren't any tarballs as yet. Nor will the `make` command below work until
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I've written a Makefile. It's coming, sometime. Sorry ;-)
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$ git clone git://github.com/fluffle/ca-scripts
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$ cd ca-scripts
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$ make; sudo make install
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This will by default install to `/usr/local`, either `export PREFIX=/path` or
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`make PREFIX=/path; sudo make PREFIX=/path install` to change this to an
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alternative location.
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Creating a Certificate Authority
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--------------------------------
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Before running **ca-init**(1), a configuration file for the CA scripts must be
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created. This configuration file sets up some templating variables that will
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be present in certificates created for this CA, such as the domain, CA name,
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and the root directory which will be populated with the generated certificates.
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An example configuration file is provided with the scripts, and the comments
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should be self-explanatory.
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By default the CA scripts will read `/etc/ca-scripts.conf`. This is fine for
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creating a single CA serving a single domain with no intermediary certificates,
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but for a more complex setup a directory of configuration files will probably
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be needed. Some settings are required, namely the **CA\_HOME**, **CA\_DOMAIN**,
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and **CA\_DN\_\*** variables, while others can be inferred from these or have
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sensible defaults set. See **ca-scripts.conf**(5) for more detail on these.
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Once the configuration has been created the initial CA setup can be performed
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with **ca-init(1)**, but please note that the path set in **CA\_HOME** must exist
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and be writeable before it will run correctly. It is recommended (but not in an
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way required) to create an unprivileged "ssl" user to run all the scripts as, so
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the permissions are correctly set. A number of subdirectories will be set
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up underneath this root, and an openssl configuration file, certificate and
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private key will be generated. This key can be 3DES encrypted for security.
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Optionally, it is possible to split the initial setup process so that the
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directory structure and openssl configuration generation can be done in a
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seperate step to the generation of the CA certificates, so that the config can
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be manually edited. To fully understand it's contents you're unfortunately
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going to need to read the following:
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* [**ca**(1ssl)](http://www.openssl.org/docs/apps/ca.html)
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* [**req**(1ssl)](http://www.openssl.org/docs/apps/req.html)
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* [**x509**(1ssl)](http://www.openssl.org/docs/apps/x509.html)
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* [**config**(5ssl)](http://www.openssl.org/docs/apps/config.html)
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* [**x509v3\_config**(5ssl)](http://www.openssl.org/docs/apps/x509v3_config.html)
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Particularly important are the x509v3 extensions present in the certificate,
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which are defined in the "ca\_x509\_extensions" section of the config file.
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Creating a certificate
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----------------------
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The **ca-create-cert**(1) script can generate three "types" of certificate:
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*server* certificates for securing a service with SSL/TLS; *client* certificates
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for authenticating a client to these services; and *user* certificates for
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authentication, S/MIME e-mail signing or encryption, and code signing. There
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are minor but important differences in the key usage extensions present in
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these different certificate types, details can be found in the documentation
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for **ca-create-cert**(1).
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**ca-create-cert**(1) takes a number of options to customise the generated
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certificate. The *--type* option is mandatory, and for *server* certs it is very
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likely that the *--alt-name* option will be useful to set X.509v3 subjectAltName
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DNS records for other hostnames for the server. Both the server hostname and
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any alternative names will be fully-qualified to **CA\_DOMAIN** if they do not
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contain any dots, but if unqualified names are passed in they are also
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preserved as alternative DNS names in the certificate. The private key may be
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encrypted with 3DES, and optionally the certificate, key, and CA certificate
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can be bundled together into a PKCS#12 format certificate archive. By default
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certificates are valid for 365 days from signing, but this may be changed with
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the *--days* option.
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The certificate's DN can be completely changed from the defaults provided by
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**ca-scripts.conf**(5), but be wary as by default the generated openssl config
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file requires that the country (C) and organisation (O) fields match those of
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the CA certificate. A comment may also be set that will show up in user browsers
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when they click on their padlock icons to examine the certificate's properties.
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As with the CA setup, the steps to generate the certificate can be split up so
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that configurations that are created from templates can be edited beforehand.
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Renewing a certificate
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----------------------
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Certificates are renewed using **ca-renew-cert**(1). This script currently
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does some painful certificate manipulation that is not strictly necessary in
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most cases, and may in fact decrease SSL security slightly. This is done because
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the normal renewal process re-generates the certificate signing request and
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thus creates a new public/private keypair. If the certificates are used for
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S/MIME encryption or code signing, this renders all the encrypted e-mail
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unreadable and requires you to re-sign the code with your new private key.
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To avoid this, **ca-renew-cert**(1) re-signs the old certificate request with
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a new expiry date using the extensions generated when the old certificate was
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signed. In the future it is possible (even likely) that this renewal method
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will only be used on *user* type certificates, and the *server* and *client*
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types will be renewed normally. If the current renewal method doesn't provide
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sufficient security, the current certificate should be revoked and a new one
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generated that is valid for the correct period of time using the *--days* option
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to **ca-create-cert**(1).
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As with the certificate creation script the *--type* option is mandatory for
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**ca-renew-cert**(1), but the argument may be either a hostname, a username or a
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path to a certificate. Internally this will be resolved to the correct
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information required for certificate renewal.
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Revoking a certificate
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----------------------
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To revoke a certificate and re-generate the CA certficate revocation list in
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both PEM and DER encodings, invoke **ca-revoke-cert**(1), again providing the
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*--type* option and either the hostname, username or the path to the certificate
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to be revoked. Along with **ca-init**(1) this script can optionally generate a
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basic HTML template to serve the CA certificate and CRL with verifiable MD5 and
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SHA1 checksums.
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