95 lines
5.5 KiB
Text
95 lines
5.5 KiB
Text
1. Creating a Certificate Authority.
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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, and
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CA_DN_* variables, while others can be inferred from these or have sensible
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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 and be
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writeable before it will run correctly. It is recommended (but not in any way
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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 ca(1ssl), req(1ssl), x509(1ssl), config(5ssl), and
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x509v3_config(5ssl). Particularly important are the x509v3 extensions present
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in the certificate, which are defined in the "ca_x509_extensions" section of
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the config file.
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2. Creating a certificate.
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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 extension
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templates provided with the scripts.
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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 x509v3 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 file
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requires that the country (C) and organisation (O) fields match those of the CA
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certificate. A comment may also be set that will show up in user browsers when
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they click on their padlock icons to examine the certificate's properties. As
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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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3. Renewing a certificate.
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Certificates are renewed using ca-renew-cert(1). This script currently does
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some painful certificate manipulation that is not strictly necessary in most
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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 a
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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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4. Revoking a certificate.
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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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